Tait TEL0049 One way paging transmitters T857-26-1010 & T857-26 User Manual 8c500 a4 bk

Tait Limited One way paging transmitters T857-26-1010 & T857-26 8c500 a4 bk

Manual

M850-00CICopyright TEL 31/09/98Part C T856 Transmitter & T857 ExciterThis part of the manual is divided into six sections, as listed below. There is a detailedtable of contents at the start of each section.Section Title1 General Information2 Circuit Operation3 Initial Tuning & Adjustment4 Functional Testing5 Fault Finding6 PCB Information
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M850-00T856/857 General InformationC1.1Copyright TEL 31/09/981 T856/857 General InformationThis section provides a brief description of the T856 transmitter and T857 exciter, alongwith detailed specifications and a list of types available.The following topics are covered in this section.Section Title Page1.1 Introduction 1.71.21.2.11.2.21.2.31.2.41.2.4.11.2.4.21.2.4.31.2.51.2.61.2.6.11.2.6.21.2.6.3SpecificationsIntroductionGeneralRF SectionAudio ProcessorInputsModulation CharacteristicsCTCSSMicrocontrollerTest StandardsEuropean Telecommunication StandardDTI CEPT Recommendation T/R-24-01Telecommunications Industry Association1.81.81.81.91.101.101.111.111.111.121.121.121.121.3 Product Codes 1.131.4 T856 Standard Product Range 1.141.5 T857 Standard Product Range 1.15Figure Title Page1.1 T856 Main Circuit Block Identification 1.41.2 T856 Front Panel Controls 1.41.3 T857 Main Circuit Block Identification 1.61.4 T857 Front Panel Controls 1.6
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M850-00T856/857 General InformationC1.7Copyright TEL 31/09/981.1 IntroductionThe T856 is a synthesised, microprocessor controlled FM base station transmitterdesigned for single or multichannel operation in the 400 to 520MHz frequency range1with a standard power output of 25W. The RF section of the transmitter comprises a fre-quency synthesiser which provides 100mW of frequency modulated RF drive to a twostage, wide band output driver followed by a 25W power amplifier. A thermal shut-down feature is provided in the T856 in case operating temperatures exceed acceptablelevels.The T857 is a synthesised, microprocessor controlled FM base station exciter designedfor single or multichannel operation in the 400 to 520MHz frequency range1. With astandard power output of only 1W, the exciter is designed for use with the T858 50W orT859 100W power amplifiers. The RF section of the exciter comprises a frequency syn-thesiser which provides 100mW of frequency modulated RF drive to a two stage, wideband output amplifier.A wide selection of audio characteristics may be obtained from the audio processor.Optional circuit blocks are an audio compressor and a pre-emphasis stage. They can bebypassed or linked to one or both audio inputs, and then back into the remaining audiocircuitry in almost any combination. All audio processor options are link selectable.The synthesiser frequency is programmed via the serial communications port. Eightchannel select lines are accessible via an optional D-range connector (D-range 2 -T800-03-0000) at the rear of the set.All components except those of the VCO are mounted on a single PCB. This is securedto a die-cast chassis which is divided into compartments to individually shield each sec-tion of circuitry. Access to both sides of the main circuit board is obtained by removingeach of the chassis lids. There is provision within the chassis to mount small optionPCBs.The front panel controls include line sensitivity, microphone socket and carrier switch.This switch turns on the carrier (unmodulated) as an aid to servicing.The T856 and T857 are both 60mm wide and each occupies a single space in a Tait rackframe, which has the ability to accommodate up to seven standard modules.1. Although capable of operating over the 400-520MHz frequency range, the T856 and T857 have an 8MHz switching range (see Section 1.2.3 and Section 3.1).
C1.8T856/857 General InformationM850-0029/02/00 Copyright TEL1.2 Specifications1.2.1 IntroductionThe performance figures given are minimum figures, unless otherwise indicated, forequipment tuned with the maximum switching range and operating at standard roomtemperature (+22°C to +28°C) and standard test voltage (13.8V DC).Where applicable, the test methods used to obtain the following performance figuresare those described in the EIA and ETS specifications. However, there are severalparameters for which performance according to the CEPT specification is given. Referto Section 1.2.6 for details of test standards.Details of test methods and the conditions which apply for Type Approval testing in allcountries can be obtained from Tait Electronics Ltd.The terms "wide bandwidth", "mid bandwidth" and "narrow bandwidth" used in thisand following sections are defined in the following table.1.2.2 GeneralNumber Of Channels .. 128 (standard)1Supply Voltage:Operating Voltage .. 10.8 to 16V DC Standard Test Voltage .. 13.8V DC Polarity .. negative earth only Polarity Protection .. crowbar diode Line Keying Supply (if required) .. -50V DCSupply Current:Transmit - T856 .. 5.5A (typical)- T857 .. 750mAStandby - T856 .. 165mA (typical)- T857 .. 150mA (typical)Operating Temperature Range .. -20°C to +60°CChannel Spacing Modulation100% Deviation ReceiverIF BandwidthWide Bandwidth 25kHz ±5.0kHz 15.0kHzMid Bandwidth 20kHz ±4.0kHz 12.0kHzNarrow Bandwidth 12.5kHz ±2.5kHz 7.5kHz1. Additional channels may be factory programmed. Contact your nearest Tait Dealer or Customer Service Organisation.
M850-00T856/857 General InformationC1.9Copyright TEL 29/02/00Dimensions: Height .. 183mm Width .. 60mm Length .. 322mmWeight .. 2.1kgTime-Out Timer (optional) .. 0 to 5 minutes1 adjustable in 10 sec-ond stepsTail Timer .. 0 to 5 seconds adjustable in 100ms2stepsTransmit Key Time .. <30ms Transmit Lockout Timer .. 0 to 1 minute adjustable in 10 secondsteps1.2.3 RF SectionFrequency Range .. 400-520MHz (refer to Section 1.4 andSection 1.5)Modulation Type .. FMFrequency Increment .. 5 or 6.25kHzSwitching Range .. 8MHz (i.e. ±4MHz from the centrefrequency)Load Impedance .. 50 ohmsFrequency Stability .. ±1ppm, -20°C to +60°C (see also Section 1.4 and Section 1.5)Adjacent Channel Power (full deviation): Wide Bandwidth (WB) .. -75dBc(±25kHz/15kHz B/W) Mid Bandwidth (MB) .. -70dBc(±20kHz/12kHz B/W)Narrow Bandwidth (NB) .. -65dBc(±12.5kHz/7.5kHz B/W)Transmitter Switching .. complies with ETS 300 1131. Adjustable from 0 to 10 minutes in PGM800Win version 2.12 and later.2. Adjustable in 20ms steps in PGM800Win version 2.12 and later.
C1.10T856/857 General InformationM850-0029/02/00 Copyright TELTransmitter Side Band Noise:(no modulation, 15kHz bandwidth) At ±25kHz .. -95dBc At ±1MHz .. -105dBcIntermodulation .. -40dBc with interfering signal of-30dBc.. -70dBc with 25dB isolation& interfering signal of -30dBc(PA with output isolator)T856 Mismatch Capability: Ruggedness .. refer to your nearest Tait Dealer orCustomer Service Organisation Stability .. 3:1 VSWR (all phase angles)Radiated Spurious Emissions:Transmit .. -36dBm to 1GHz -30dBm 1GHz to 4GHz Standby .. -57dBm to 1GHz -47dBm 1GHz to 4GHzConducted Spurious Emissions: (T856 Only)Transmit .. -36dBm to 1GHz -30dBm 1GHz to 4GHz Standby .. -57dBm to 1GHz -47dBm 1GHz to 4GHzPower Output:T856 - Rated Power .. 25W (see Duty Cycle)- Range Of Adjustment .. 5-25WT857 .. 1W ±300mWDuty Cycle (T856 Only) .. 100% @ 25W at +25°C.. 25% @ 25W at +60°C.. 100% @ 10W at +40°C1.2.4 Audio Processor1.2.4.1 InputsInputs Available .. line, microphone and CTCSSLine Input: Impedance .. 600 ohms (balanced) Sensitivity (60% modulation @ 1kHz)- With Compressor .. -50dBm Without Compressor .. -30dBm
M850-00T856/857 General InformationC1.11Copyright TEL 29/02/00Microphone Input: Impedance .. 600 ohms Sensitivity (60% modulation @ 1kHz)- With Compressor .. -70dBm Without Compressor .. -50dBm1.2.4.2 Modulation CharacteristicsFrequency Response .. flat or pre-emphasised (optional) (below limiting)Line And Microphone Inputs: Pre-emphasised Response- Bandwidth .. 300Hz to 3kHz (WB & MB).. 300Hz to 2.55kHz (NB)Below Limiting .. within +1, -3dB of a 6dB/octavepre-emphasis characteristic Flat Response .. within +1, -2dB of output at 1kHzAbove Limiting Response .. within +1, -2dB of a flat response(ref. 1kHz)Distortion .. 2% max.Hum And Noise: Wide Bandwidth .. -55dB (300Hz to 3kHz [EIA]) typical Mid Bandwidth .. -54dB (CEPT)Narrow Bandwidth .. -50dB (CEPT) Compressor (optional): Attack Time .. 10ms Decay Time .. 800ms Range .. 50dB1.2.4.3 CTCSSStandard Tones .. all 37 EIA group A, B and C tonesplus 13 commonly used tonesFrequency Error .. 0.08% max.(from EIA tones)Generated Tone Distortion .. 1.2% max.Generated Tone Flatness .. flat across 67 to 250.3Hz to within 1dBModulation Level .. adjustableModulated Distortion .. <5%
C1.12T856/857 General InformationM850-0029/02/00 Copyright TEL1.2.5 MicrocontrollerAuxiliary Ports:Open Drain Type .. capable of sinking 2.25mA via 2k2ΩVds max. .. 5V1.2.6 Test StandardsWhere applicable, this equipment is tested in accordance with the following standards.1.2.6.1 European Telecommunication StandardETS 300 086 January 1991Radio equipment and systems; land mobile service; technical characteristics and testconditions for radio equipment with an internal or external RF connector intended pri-marily for analogue speech.ETS 300 113 March 1996Radio equipment and systems; land mobile service; technical characteristics and testconditions for radio equipment intended for the transmission of data (and speech) andhaving an antenna connector.ETS 300 219 October 1993Radio equipment and systems; land mobile service; technical characteristics and testconditions for radio equipment transmitting signals to initiate a specific response in thereceiver.ETS 300 279 February 1996Radio equipment and systems; electromagnetic compatibility (EMC) standard for pri-vate land mobile radio (PMR) and ancillary equipment (speech and/or non-speech).1.2.6.2 DTI CEPT Recommendation T/R-24-01Annex I: 1988Technical characteristics and test conditions for radio equipment in the land mobileservice intended primarily for analogue speech.Annex II: 1988Technical characteristics of radio equipment in the land mobile service with regard toquality and stability of transmission.1.2.6.3 Telecommunications Industry AssociationANSI/TIA/EIA-603-1992Land mobile FM or PM communications equipment measurement and performancestandards.
M850-00T856/857 General InformationC1.13Copyright TEL 29/02/001.3 Product CodesThe three groups of digits in the T850 Series II product code provide information aboutthe model, type and options fitted, according to the conventions described below.The following explanation of T850 Series II product codes is not intended to suggest thatany combination of features is necessarily available in any one product. Consult yournearest Tait Dealer or Customer Service Organisation for more information regardingthe availability of specific models, types and options.ModelThe Model group indicates the basic function of the product, as follows:T85X-XX-XXXX T855 receiverT856 25W transmitterT857 exciterT858 50W power amplifierT859 100W power amplifierTypeThe Type group uses two digits to indicate the basic RF configuration of the product.The first digit in the Type group designates the frequency range:T85X-XX-XXXX ’1’ for 400-440MHz’2’ for 440-480MHz’3’ for 480-520MHzThe second digit in the Type group indicates the channel spacing:T85X-XX-XXXX ’0’ for wide bandwidth (25kHz)’3’ for mid bandwidth (20kHz)’5’ for narrow bandwidth (12.5kHz)’6’ for United States market onlyOptionsT85X-XX-XXXX The Options group uses four digits and/or letters to indicateany options that may be fitted to the product. This includesstandard options and special options for specific customers.’0000’ indicates a standard Tait product with no options fitted.The large number of options precludes listing them here.
C1.14T856/857 General InformationM850-0029/02/00 Copyright TEL1.4 T856 Standard Product RangeThe following table lists the range of standard T856 types (i.e. no options fitted) availa-ble at the time this manual was published. Consult your nearest Tait Dealer or Cus-tomer Service Organisation for more information.Caution:T856-1X-XXXX Product TypesThe 406 to 406.1MHz frequency range is reserved worldwide for use byDistress Beacons. Do not program transmitters to operate in this fre-quency range.You can identify the transmitter type by checking the product code printed on a label onthe rear of the chassis (Figure 1.1 in Part A shows typical labels). You can further verifythe transmitter type by checking the placement of an SMD resistor in the table that isscreen printed onto the PCB (refer to Section 6.1 for more details). Frequency Range (MHz) 400-440Deviation (kHz) 2.5 2.5 4 5TCXO ±1ppm -20°C to +60°C ••••Transmitter Type: T856- 16-0000aa. United States market only.15-0000 13-0000 10-0000Frequency Range (MHz) 440-480Deviation (kHz) 2.5 2.5 4 5TCXO ±1ppm -20°C to +60°C ••••Transmitter Type: T856- 26-0000a25-0000 23-0000 20-0000Frequency Range (MHz) 480-520Deviation 2.5 2.5 5TXCO ±1ppm -20° to +60°C •••Transmitter Type: T856- 36-0000a35-0000 30-0000
M850-00T856/857 General InformationC1.15Copyright TEL 29/02/001.5 T857 Standard Product RangeThe following table lists the range of standard T857 types (i.e. no options fitted andcyclic keying disabled) available at the time this manual was published. Consult yournearest Tait Dealer or Customer Service Organisation for more information.Caution:T857-1X-XXXX Product TypesThe 406 to 406.1MHz frequency range is reserved worldwide for use byDistress Beacons. Do not program exciters to operate in this frequencyrange.You can identify the exciter type by checking the product code printed on a label on therear of the chassis (Figure 1.1 in Part A shows typical labels). You can further verify theexciter type by checking the placement of an SMD resistor in the table that is screenprinted onto the PCB (refer to Section 6.1 for more details). Frequency Range (MHz) 400-440Deviation (kHz) 2.5 2.5 4 5TCXO ±1ppm -20°C to +60°C ••••Exciter Type: T857- 16-0000aa. United States market only.15-0000 13-0000 10-0000Frequency Range (MHz) 440-480Deviation (kHz) 2.5 2.5 4 5TCXO ±1ppm -20°C to +60°C ••••Exciter Type: T857- 26-0000a25-0000 23-0000 20-0000Frequency Range (MHz) 480-520Deviation 2.5 2.5 5TXCO ±1ppm -20° to +60°C •••Exciter Type: T857- 36-0000a35-0000 30-0000
C1.16T856/857 General InformationM850-0031/09/98 Copyright TEL
M850-00T856/857 Circuit OperationC2.1Copyright TEL 31/09/982 T856/857 Circuit OperationThis section provides a basic description of the circuit operation of the T856 transmitterand T857 exciter.Note:Unless otherwise specified, the term "PGM800Win" used in this and follow-ing sections refers to version 2.00 and later of the software.Refer to Section 6 where the parts lists, grid reference index and diagrams will providedetailed information on identifying and locating components and test points on themain PCB. The parts list and diagrams for the VCO PCB are in Part E.The following topics are covered in this section.Section Title Page2.1 Introduction 2.32.2 Microcontroller 2.42.32.3.1Synthesised Local OscillatorTwo Point Modulation2.52.62.42.4.1VCOVCO Supply2.72.72.52.5.12.5.22.5.32.5.42.5.5Audio ProcessorGeneralAudio InputsKeying InputsCompressor (Automatic Level Control (ALC))Outputs To Modulators2.82.82.82.92.92.92.6 Power Supply & Regulator Circuits 2.102.7 Transmit Timers 2.112.8 T856 Drive Amplifier & PA 2.122.9 T857 Exciter Drive Amplifier 2.13
C2.2T856/857 Circuit OperationM850-0031/09/98 Copyright TELFigure Title Page2.12.22.32.42.52.62.72.8T856 High Level Block DiagramT857 High Level Block DiagramT856/857 Microcontroller Block DiagramT856/857 Synthesiser Block DiagramT856/857 Two Point ModulationT856/857 Audio Processor Block DiagramT856/857 Power Supply & Regulators Block DiagramT856/857 Transmit Timers2.32.32.42.52.62.82.102.11
M850-00T856/857 Circuit OperationC2.3Copyright TEL 31/09/982.1 IntroductionThe individual circuit blocks which make up the T856 and T857 are:• synthesiser•VCO• audio processor• drive amplifier• power amplifier (T856 only)• voltage regulators. Each of these circuit blocks is set in its own shielded compartment, formed as an inte-gral part of the main chassis.The configuration of the circuit blocks may be seen on a functional level in Figure 2.1and Figure 2.2. Refer to the circuit diagrams in Section 6.2 (T856) or 6.3 (T857) for moredetail.Figure 2.1 T856 High Level Block DiagramFigure 2.2 T857 High Level Block DiagramRampGen.TimeDelayTimeDelayTimeDelayAudioProcessorSynthesiser +22dBmReferenceOscillator12.8MHzMicrophoneLineTransformerLockDetectPINSwitchPowerControlDriveAmp. PAVCOGateDirectionalCoupler Low PassFilterExciterOutput(+30dBm to +33dBm) TransmitterOutput(25W)Tx Reg&AudioProcessorSynthesiser +22dBmReferenceOscillator12.8MHzMicrophoneLineTransformerLockDetectPINSwitchSwitchingControlDriveAmp.GateExciterOutput(+28dBm to+31dBm)&RampGen.Tx Reg VCOTimeDelayTimeDelayLow PassFilterPA Control Signal(via exciter RF coax)
C2.4T856/857 Circuit OperationM850-0029/02/00 Copyright TEL2.2 Microcontroller(Refer to the microcontroller circuit diagram (sheet 8) in Section 6.2 or 6.3.)Figure 2.3 T856/857 Microcontroller Block DiagramOverall system control of the T856/857 is accomplished by the use of a member of the80C51 family of microcontrollers (IC810). It runs from internal ROM and RAM, thusleaving all four ports free for input/output functions.Non-volatile data storage is achieved by serial communication with a 16kBit EEPROM(IC820). This serial bus is also used by the microcontroller to program the synthesiser(IC740) and deviation control EPOTS (IC220).The main tasks of the microcontroller are as follows:• program the synthesiser and EPOT;• interface with the PGM800Win programming software at 9600 baud via theserial communication lines on D-range 1 (PL100) & D-range 2;• monitor channel change inputs from D-range 2;• generate timing waveforms for CTCSS encoding;• coordinate and implement timing control of the exciter/transmitter.• control the front panel "Supply" LED (refer to Section 5.3).5V Reset5V DigitalRegulator Watchdog ResetChannelSelectPortAuxiliaryOutputPortMicrocontroller12.8MHzClockMicrocontroller CavityCTCSS ToneExternalSerialPortEEPROM SynthesiserDual DigitalPotentiometerCTCSSEncoderConverter
M850-00T856/857 Circuit OperationC2.5Copyright TEL 31/09/982.3 Synthesised Local Oscillator(Refer to the synthesiser circuit diagram (sheet 7) in Section 6.2 or 6.3 and the VCO cir-cuit diagram in Part E.)Figure 2.4 T856/857 Synthesiser Block DiagramThe synthesiser (IC740) employs a phase-locked loop (PLL) to lock a voltage controlledoscillator (VCO) to a given reference frequency. The synthesiser receives the dividerinformation from the control microprocessor via a 3 wire serial bus (clock, data, enable).When the data has been latched in, the synthesiser processes the incoming signals fromthe VCO buffer (fin) and the phase modulator (fref).A reference oscillator at 12.8MHz (=IC700) is buffered (IC710 pins 3 & 4) and divideddown to 200kHz (IC730). This 200kHz square wave is then summed with the modulat-ing audio and passed to an integrator (IC720 pins 9 & 8, Q710, Q720). This produces aramping waveform which is centred around a DC level determined by the incomingaudio. IC720 pins 5 & 6 perform as a comparator, ultimately producing a phase-modu-lated 200kHz square wave. This is followed by another phase shifting stage (IC720 pins3 & 4, Q730, Q740), before being divided down to 6.25kHz or 5kHz within the synthe-siser IC (IC740).A buffered output of the VCO (Q795) is divided with a prescaler and programmabledivider which is incorporated into the synthesiser chip (IC740). This signal is comparedwith the phase modulated reference signal at the phase detector (also part of the synthe-siser chip). The phase detector outputs drive a balanced charge pump circuit (Q760,Q770, Q775, Q780, Q785) and active loop filter (IC750 pins 5, 6 & 7, Q790) which pro-duces a DC voltage between 0V and 20V to tune the VCO. This VCO control line is fur-ther filtered to attenuate noise and other spurious signals. Note that the VCO frequencyincreases with increasing control voltage.If the synthesiser loop loses lock, a pulsed signal appears at LD (pin 2) of IC740. Thissignal is filtered and buffered by IC750 pins 1, 2 & 3, producing the Lock-Detect signalused to shut off the power supply to the drive amplifier. IC750 pin 1 is at 20V when thesynthesiser is out of lock./RReferenceDivider12.8MHzReferenceOscillator FixedDivider/64PhaseModulatorRefModPhaseDetector ChargePump LoopFilterFREQUENCY SYNTHESISER ICSerialBusClkDataEn Controller/NProgrammableDivider64/65PrescalerVCO PCBVCO ModulationVCO Buffer OutputBuffer+22dBmL.O.Divider BufferfreffinΣ
C2.6T856/857 Circuit OperationM850-0029/02/00 Copyright TEL2.3.1 Two Point ModulationFrequency modulation occurs by modulating both the VCO input and the synthesiserreference input. This process is called two point modulation and ensures a flat modula-tion response from 67Hz to 3kHz (2.55kHz for narrow bandwidth).The PLL has a fast response time, allowing a Tx key-up time of <30ms. Because of thisfast response time the PLL sees lower modulation frequencies superimposed on theVCO as an error and corrects for it, resulting in no modulation on the carrier. At modu-lation frequencies greater than 300Hz the loop cannot correct fast enough and modula-tion is seen on the carrier. The response of the loop to VCO modulation is shown by f2in Figure 2.5 below.To achieve low frequency modulation, the reference oscillator is also modulated so thatthe phase detector of IC740 detects no frequency error under modulation. Thus, thesynthesiser loop will not attempt to correct for modulation and the audio frequencyresponse of the transmitter remains unaffected. The response of the loop to referencefrequency modulation is shown by f1 in Figure 2.5.The reference modulation is controlled by a 256-step 10k electronic potentiometer(EPOT) which is adjustable via PGM800Win. The EPOT is made up of 256 resistive sec-tions (representing approximately 39Ω each) which can be individually addressed bythe microcontroller. Each section can be switched in or out of circuit to achieve therequired total resistance, thus giving control of the reference modulation.Figure 2.5 T856/857 Two Point Modulation12ffTCXO VCODeviationFrequency
M850-00T856/857 Circuit OperationC2.7Copyright TEL 31/09/982.4 VCO(Refer to the VCO circuit diagram in Part E.)The VCO transistor (Q1) operates in a common emitter configuration, with an LC tankcircuit coupled between its gate and drain to provide the feedback necessary for oscilla-tion. The VCO control voltage from the loop filter (IC750) is applied to the varicaps(D1-D2) to facilitate tuning within an 8MHz band of frequencies. A trimcap (C6) is usedfor coarse tuning of the VCO. The output from the oscillator circuit drives a cascodeamplifier stage (Q2, Q3) which supplies +10dBm (typically) to a further stage of amplifi-cation, Q5. This is the final amplifier on the VCO PCB, and delivers +20dBm (typically)to the exciter drive amplifier.A low level "sniff" is taken from the input to Q5 and used to drive the divider buffer forthe synthesiser (IC740).The VCO operates at the actual output frequency of the exciter, i.e. there are no multi-plier stages. It is modulated by superimposing the audio signal onto the control voltageand by phase modulating the reference signal.2.4.1 VCO Supply The VCO is supplied from two switched +9V supplies under the control of the Tx-Reg.supply.The VCO and buffer amplifier are supplied from one +9V switched supply by Q540 viathe C multiplier (Q550, C530 on the T856 and C550 on the T857).The output amplifier is supplied from the other +9V supply by Q520, Q530, and Q510.A delay circuit holds the VCO on for a short time after the Tx-Reg. supply has beenswitched off. This is to allow the RF power circuits (both exciter and PA) to ramp downin the correct manner before the VCO is switched off.
C2.8T856/857 Circuit OperationM850-0029/02/00 Copyright TEL2.5 Audio Processor(Refer to the audio processor circuit diagram (sheet 2) in Section 6.2 or 6.3.)Figure 2.6 T856/857 Audio Processor Block Diagram2.5.1 GeneralThe audio processor comprises several link selectable circuit blocks which may be con-figured in a variety of combinations to suit individual requirements. The pre-emphasisnetwork and compressor may be linked individually or cascaded between either or bothaudio inputs and the limiter.Refer to Section 3.5.1 for linking details.2.5.2 Audio InputsTwo audio inputs are available: one from a 600 ohm balanced (or unbalanced) line, andthe other from a local microphone. The microphone signal is passed first to a pre-ampli-fier (Q210) and ultimately to a multiplexer (IC240), but in between may pass throughthe compressor (depending on the linking details). The line transformer is also con-nected to the multiplexer and is disabled by the microphone PTT switch.A third input for external CTCSS tones is also provided.Pre-emphasis346BC56434253357128NHMIELJD461mic.lineMultiplexerInputsOutputOutputInhibitAudio 1 Audio 2CompressorLinkLinkLinkTx EnableΣCarrierOpto-KeyTx KeyPTTMicrophoneInputLine InputMicrophonePre-amp.Opto-couplerLinkPL205PL215PL220PL210LimiterSet DeviationCTCSSLow PassFilterRef. Mod. AdjustIntegratorDigital Pot. (EPOT)Digital Pot. (EPOT)BufferOutputTo VCO Ref.Mod.Constant Current Sink+_
M850-00T856/857 Circuit OperationC2.9Copyright TEL 29/02/002.5.3 Keying InputsThere are four ways to key the exciter: • pulling the Tx-Key line low (pin 13 on D-range 1 [PL100]) at the rear of the set);• pushing the "Carrier" button on the front panel - this will inhibit all audio;• using the PTT button on the local microphone, disabling audio from the line;• via the opto-key inputs (pins 11 and 12 on D-range 1 [PL100]) when electricalisolation is required. This features a constant current sink (Q270) to ensure reli-able activation of the opto-coupler (IC250) at low keying voltages.2.5.4 Compressor (Automatic Level Control (ALC))The input signal is fed via a current controlled attenuator (Q230, Q220) to a high gainstage (IC230) from which the output signal is taken. This signal is passed to a compara-tor (IC230) which toggles whenever the audio signal exceeds a DC threshold deter-mined by RV220. Thus, the comparator produces a square wave whose mark-spaceratio is determined by the amplitude of the audio signal. This square wave pumps upthe reservoir capacitor (C233) which controls the attenuator (Q230, Q220), thus complet-ing the feedback loop.The compression level is set by adjustment of the comparator threshold (RV220).Note:Although the high dynamic range of the compressor allows the use of verylow audio signal levels, such conditions will be accompanied by a degrada-tion of the signal-to-noise ratio. Very low audio input levels should there-fore be avoided where possible.2.5.5 Outputs To ModulatorsThe output signal from the limiter (IC210, IC230) is summed with a CTCSS tone at asumming amplifier (IC260). The signal is then low pass filtered (IC260) and split to sup-ply the two modulators.Since the VCO modulator is a true frequency modulator, its audio is simply buffered(IC260). The reference modulator, however, is a phase modulator and its audio mustfirst be integrated (IC210).It is vital that the audio levels to the modulators are accurately set, relative to eachother. Hence the inclusion of level adjustment in the reference modulator path. Onceset, adjustments to absolute deviation may be made only by IC220, a 256-step 10k elec-tronic potentiometer (EPOT), which is controlled via PGM800Win. The EPOT is madeup of 256 resistive sections (representing approximately 39Ω each) which can be indi-vidually addressed by the microcontroller. Each section can be switched in or out of cir-cuit to achieve the required total resistance, thus adjusting the absolute deviation level.
C2.10T856/857 Circuit OperationM850-0029/02/00 Copyright TEL2.6 Power Supply & Regulator Circuits (Refer to the regulators circuit diagram (sheet 6) in Section 6.2 or 6.3.)Figure 2.7 T856/857 Power Supply & Regulators Block DiagramThe T856 and T857 are designed to operate from a 10.8-16V DC supply (13.8V nominal).A 5.3V regulator (IC630) runs directly from the 13.8V rail, driving much of the synthe-siser circuitry. It is also used as the reference for a DC amplifier (IC640, Q630, Q620)which provides a medium current capability 9V supply. The T856 has a regulator(IC370) which produces 9V for use in the exciter and audio circuits.A switching power supply (Q660, Q670) runs from the 9V supply and provides a lowcurrent capability +20V supply. This is used to drive the synthesiser loop filter (IC750),giving a VCO control voltage range of up to 20V.Ultimate control of the transmitter is via the Tx-Reg. supply, switched from 9V by Q610.This is enabled via the Tx-Enable signal from the audio processor, and microprocessor. A crowbar diode is fitted for protection against connection to a power supply of incor-rect polarity. It also provides transient overvoltage protection.Note:A fuse must be fitted in the power supply line for the diode to provide effec-tive protection.CrowbarDiode LVI5VRegDCAmp SwitchingPS 5V DigRegPowerSwitch13.8VNom. 5V 5V Dig9V 20V13.8V Nom.From RearD-RangeTx EnableBufferTx Reg.+9VµPWatchdogTimerMicro-controllerµPReset
M850-00T856/857 Circuit OperationC2.11Copyright TEL 29/02/002.7 Transmit TimersThe transmit tail timer, transmit timeout timer and transmit lockout timer can all be setfrom PGM800Win. The fields for setting these are found on the system informationpage. These three timers operate as follows (refer also to Figure 2.8):Figure 2.8 T856/857 Transmit TimersTimer Function AdjustmentTransmit Tail Sets the tail time during which the transmitter stays keyed after the exter-nal key source has been removed.0-5 seconds in 100ms stepsaa. Adjustable in 20ms steps in PGM800Win version 2.12 and later.Transmit Timeout Sets the maximum continuous trans-mission time. Once the timer has timed out, the transmitter must be keyed again, unless prevented by the transmit lockout timer.0-300 secondsb in 10 second stepsb. Adjustable from 0 to 600 seconds in PGM800Win version 2.12 and later.Transmit Lockout Sets the period of time that must elapse after a timeout before the trans-mitter can re-transmit. Once the timer has timed out, the transmitter can be keyed again.0-60 seconds in 10 second stepsOnLockout TimeTimeoutTimeOnTail TimeTx-EnableTx-Reg.Tx-EnableTx-Reg.
C2.12T856/857 Circuit OperationM850-0031/09/98 Copyright TEL2.8 T856 Drive Amplifier & PA(Refer to Figure 2.1 and the exciter and PA circuit diagrams (sheets 3 & 4) in Section 6.2.)The output power of the PA is maintained at a constant level via a power control loopapplied to the two-stage, wide band exciter amplifier (Q350, Q355). The forward andreverse RF power levels are sensed via a dual directional coupler and detector diodes(D440, D420 in the PA cavity). The detected DC signals are buffered (IC330 pins 3 & 5)and then summed with the ’power control’ level and fed to the control integrator (IC350pin 6). The output control voltage is buffered by Q310 and Q315, and applied to the col-lector of the wide band exciter amplifier.Note:Forward and reflected power signals are summed so that, under highVSWR, the power control will turn the output RF level down. To reduce the spurious output level when the synthesiser is out-of-lock, the Tx-Reg. andLock-Detect signals are gated to inhibit the PA control circuit and to switch off the RFsignal at the input to the drive amplifier. This is achieved by a PIN switch attenuator(D340, D380, D360).Cyclic keying control is provided by additional circuitry consisting of several timedelay, ramp and gate stages:• Q325, IC350 power ramping• Q355, Q325 Tx-Reg. and Lock-Detect gate• Q335, Q340, Q345 delay and PIN switch drive.This is to allow the RF power circuits (both exciter and PA) to ramp up and down in acontrolled manner so that minimal adjacent channel interference is generated duringthe transition.The output of the wide band amplifier is approximately 1W (+30dBm) for an input of100mW (+20dBm) from the VCO, when the power control is set to maximum.A temperature sensor (R481) is provided so that the RF output power can be reduced toa preset level when a set temperature is exceeded. This is a protection circuit (IC350 pin1, Q320) to prevent overheating, as the unit is not rated for continuous operation (referto Section 1.2.3 for duty cycle specifications).#R517, #R518 and #R519 form an attenuator to provide good VCO/exciter isolation aswell as the correct exciter drive level.The attenuator (#R395, #R396 and #R397) aids in producing the correct exciter drivelevel to the PA over the three frequency ranges.The RF output from the exciter is fed to the driver stage (Q410) and then to the final(Q420). DC is fed to the final via a low pass filter with special low frequency decou-pling. CV475 tunes the output matching across the entire band.
M850-00T856/857 Circuit OperationC2.13Copyright TEL 29/02/002.9 T857 Exciter Drive Amplifier(Refer to Figure 2.2 and the exciter circuit diagram (sheet 3) in Section 6.3.)A two-stage, wide band amplifier (Q304, Q305) provides an output level of approxi-mately 1W (+30dBm) for an input of 100mW (+20dBm) from the VCO. IC300 pin 1,Q302, and Q303 provide a 9V regulated supply for the exciter.To reduce the spurious output level when the synthesiser is out-of-lock, the Tx-Reg. andLock-Detect signals are gated to inhibit the exciter control circuit and to switch off theRF signal at the input to the drive amplifier. This is achieved by a PIN switch attenuator(D201, D202, D203).Cyclic keying control is provided by additional circuitry consisting of several timedelay, ramp and gate stages:• Q301, Q302, Q303, IC300 power ramping• Q310, Q311 Tx-Reg. and Lock-Detect gate• Q306, Q307, Q308, Q309 delay and PIN switch drive.This is to allow the RF power circuits (both exciter and PA) to ramp up and down in acontrolled manner so that minimal adjacent channel interference is generated duringthe transition.R517, R518 and R519 form a 3dB attenuator to provide good VCO/drive amplifier isola-tion as well as the correct exciter drive levelNote:The exciter provides a DC control signal to the PA via the RF coax. This isinjected via L314.
C2.14T856/857 Circuit OperationM850-0031/09/98 Copyright TEL
M850-00T856/857 Initial Tuning & AdjustmentC3.1Copyright TEL 29/02/003 T856/857 Initial Tuning & AdjustmentCaution:This equipment contains CMOS devices which are susceptible to dam-age from static charges. Refer to Section 1.2 in Part A for more infor-mation on anti-static procedures when handling these devices.The following section describes both short and full tuning and adjustment proceduresand provides information on:• channel programming • selecting required audio links • synthesiser alignment • PA alignment (T856 only)• modulator adjustment • limiter adjustment • setting line level • compressor adjustment • timer adjustment.Note:Unless otherwise specified, the term "PGM800Win" used in this and follow-ing sections refers to version 2.00 and later of the software.Refer to Figure 4.4 and Figure 4.5 which show the location of the main tuning andadjustment controls. Refer also to Section 6 where the parts lists, grid reference indexand diagrams will provide detailed information on identifying and locating compo-nents and test points on the main PCB. The parts list and diagrams for the VCO PCB arein Part E.Section Title Page3.1 Introduction 3.33.2 Channel Programming 3.33.3 Test Equipment Required 3.43.43.4.13.4.23.4.33.4.43.4.53.4.63.4.7Short Tuning ProcedureIntroductionSynthesiser AlignmentOutput Power Adjustment (T856 Only)Two Point Modulation AdjustmentCTCSS Encoder (If Used)FM Deviation (Limiter) AdjustmentLine-in Level Adjustment3.53.53.53.53.63.73.73.7
C3.2T856/857 Initial Tuning & AdjustmentM850-0029/02/00 Copyright TEL3.53.5.13.5.2Audio Processor LinksLink DetailsTypical Options3.83.83.83.6 Synthesiser Alignment 3.93.7 PA Alignment (T856 Only) 3.103.8 Thermal Shutdown (T856 Only) 3.103.93.9.13.9.23.9.33.9.43.9.53.9.63.9.6.13.9.6.23.9.6.3Audio Processor & CTCSSTwo Point ModulationModulator AdjustmentCTCSS Encoder (If Used)Limiter AdjustmentLine Level Without CompressorCompressorCompressor On Line Input OnlyCompressor On Microphone Input OnlyCompressor On Both Line & Microphone Inputs3.113.113.113.123.123.133.133.133.133.14Figure Title Page3.13.2T856/857 Test Equipment Set-up With T800-01-0010T856/857 Test Equipment Set-up Without T800-01-00103.43.4Section Title Page
M850-00T856/857 Initial Tuning & AdjustmentC3.3Copyright TEL 31/09/983.1 IntroductionWhen you receive your T856 transmitter or T857 exciter it will be run up and workingon a particular frequency (the "default channel")1. If you want to switch to a frequencythat is within the 8MHz switching range (i.e. ±4MHz from the factory programmed fre-quency), you should only need to reprogram the transmitter/exciter with thePGM800Win software (refer to the PGM800Win programming kit and Section 3.2below). However, if you want to switch to a frequency outside the 8MHz switching range, youwill have to reprogram and re-tune the transmitter/exciter to ensure correct operation.In this case you should carry out the short tuning procedure described in Section 3.4.If you have carried out repairs or other major adjustments, you must carry out the fulltuning and adjustment procedure described in this section (except for Section 3.4). 3.2 Channel ProgrammingYou can program up to 128 channel frequencies into the transmitter/exciter’s EEPROMmemory (IC820) by using the PGM800Win software package and an IBM PC. You canalso use PGM800Win to select the transmitter/exciter’s current operating frequency (or"default channel").If the transmitter/exciter is installed in a rack frame, you can program it via the pro-gramming port in the speaker panel. However, you can also program the transmitter/exciter before it is installed in a rack frame as follows:• by using a T800-01-0010 calibration test unit;• via D-range 1;• via D-range 2 (standard T800-03-0000 auxiliary D-range only);• via SK805 (internal Micromatch connector).If you do not use the T800-01-0010, you will have to connect the PC to the transmitter/exciter via a module programming interface (such as the T800-01-0004).For a full description of the channel programming procedure, refer to the PGM800Winprogramming software user’s manual.Note:When an auxiliary D-range kit (D-range 2 - T800-03-0000) is fitted, you canalso select a channel with an external switch, such as the DIP switch on therack frame backplane PCB. Refer to Part C in the T800 Series AncillaryEquipment Service Manual (M800-00-101 or later issue) or consult yournearest Tait Dealer or Customer Service Organisation for further details.1. Use the "Read Module" function in PGM800Win to find out what the default channel is.
C3.4T856/857 Initial Tuning & AdjustmentM850-0031/09/98 Copyright TEL3.3 Test Equipment RequiredYou will need the following test equipment:• computer with PGM800Win installed• T800 programming kit• module programming interface (e.g. T800-01-0004 - optional)• 13.8V power supply• digital multimeter• audio signal generator• RF power meter• audio voltmeter x 2• modulation meter• oscilloscope (digital preferred)• 20dB or 40dB pad• T800-01-0010 calibration test unit (optional)Figure 3.1 and Figure 3.2 show typical test equipment set-ups.Figure 3.1 T856/857 Test Equipment Set-up With T800-01-0010Figure 3.2 T856/857 Test Equipment Set-up Without T800-01-0010or RF test set (optional)FrequencyCounterAudioVoltmeterRF PowerMeter OscilloscopeAF O/PModulationMeter20dB pad: exciter40dB pad: transmitterRF O/PPGM800WinPSU+13.8V-VeAudioGeneratorLine I/PCTCSS I/PΩ600AudioVoltmeterExciter/TransmitterT800CalibrationTest UnitPGM800WinSerialComPSU+13.8V-VeFrequencyCounterAudioVoltmeterRF PowerMeter OscilloscopeAF O/PModulationMeter20dB pad: exciter40dB pad: transmitterAudioGeneratorLine I/PCTCSS I/PΩ600AudioVoltmeterKeyRF O/PExciter/Transmittervia module programming interface(e.g. T800-01-0004)
M850-00T856/857 Initial Tuning & AdjustmentC3.5Copyright TEL 29/02/003.4 Short Tuning ProcedureUse this procedure only if you want to reprogram the T856/857 to a frequency outsidethe 8MHz switching range and do not intend to carry out any other major adjustmentsor repairs.3.4.1 IntroductionReprogram the operating frequency as described in the PGM800Win program-ming kit (refer to Section 3.2).Remove the top cover (nearest the handle).Set up the test equipment as described in Section 3.3.Set the links in the audio processor section as required (refer to Section 3.5).3.4.2 Synthesiser Alignment• Connect a high impedance voltmeter to the long lead of L1 in the VCO (this meas-ures the synthesiser loop voltage).• Key the transmitter by earthing the Tx-Key line.•Single Channel Tune VCO trimmer C6 for a synthesiser loop voltage of10V.Multichannel Tune VCO trimmer C6 for a synthesiser loop voltage of10V on the middle channel.If there is no middle channel, tune C6 so that the channelsare symmetrically placed around a loop voltage of 10V.All channels should lie within the upper and lower limitsof 16V and 3V respectively.Do not attempt to program channels with a greater fre-quency separation than the specified switching range of8MHz.3.4.3 Output Power Adjustment (T856 Only)Connect an RF power meter with suitable attenuation to the output socket andkey the transmitter.Turn RV310 (power control) fully clockwise.Tune #CV475 (output power trim) for maximum output power and check that thisis >30W.Adjust RV310 for the required output power (between 5 and 25W).Readjust #CV475 to reduce the supply current by up to 0.5A.
C3.6T856/857 Initial Tuning & AdjustmentM850-0029/02/00 Copyright TEL3.4.4 Two Point Modulation AdjustmentNote 1:In this and following sections deviation settings are given first for widebandwidth sets, followed by settings in brackets for mid bandwidth sets ( )and narrow bandwidth sets [ ].Note 2:The reference modulation and limiter adjustments are controlled by 256-step electronic potentiometers (EPOTs), which are adjusted via the “Refer-ence Modulation” and “Deviation” settings in PGM800Win. This allows thetwo point modulation and deviation settings to be adjusted for each chan-nel.Note 3:To optimise the modulation response across the switching range, repeatsteps 1-4 below for each channel that will be used (usually needed only fordata applications). In applications where the modulation response is lesscritical (e.g. voice use only), carry out steps 1-4 below on the middle channeland use the “EPOT Fill” option1 in PGM800Win to copy the value to theother channels.Note 4:If you are using an RF test set, turn the low pass filter off and set the highpass filter to 15kHz before beginning this procedure.1. Inject an audio signal of 300Hz 1.5V rms (+5dBm) into the CTCSS input (D-range1 (PL100) pin 8). Key the transmitter by earthing the Tx-Key line.2. Adjust the output from the audio generator to obtain ±3kHz (±2.4kHz) [±1.5kHz]deviation at 300Hz.3. Change the input frequency to 100Hz and, using PGM800Win, adjust the value ofthe “Reference Modulation” EPOT setting for the current channel to obtain ±3kHz(±2.4kHz) [±1.5kHz] deviation (you can use either the mouse or up and downarrow keys).4. Change the input frequency back to 300Hz.Repeat steps 2 and 3 above until the deviations achieved at the two input frequen-cies are within 0.2dB of each other. You will need to do this at least four times.5. Sweep the audio between 50 and 300Hz for peaks.Note:A peak between 50 and 300Hz will indicate a fault condition, i.e:- incorrect set-up or - modulation circuitry fault. The specification window is ±1dB relative to 150Hz from 67 to 260Hz.1. Use the “EDIT FILL” button on the tool bar or go to “Edit”, “Fill”, “Epot Settings” on the menu bar.
M850-00T856/857 Initial Tuning & AdjustmentC3.7Copyright TEL 29/02/003.4.5 CTCSS Encoder (If Used)Program a CTCSS tone on the default channel using PGM800Win.If you are using an RF test set, turn off the 300Hz high pass filter.Key the T856/857 with the front panel "Carrier" switch.Adjust RV805 (CTCSS level adjust) to give ±500Hz (±350Hz) [±250Hz] deviation.Set the maximum deviation as per Section 3.4.6.3.4.6 FM Deviation (Limiter) AdjustmentNote:If the T856/857 will be used over the whole 8MHz switching range, youmust set the deviation for each channel. However, if the module will beused on frequencies that cover only a 1MHz (or less) switching range, youcan set the deviation on the middle channel and use this value for all otherchannels with the “EPOT Fill” option in PGM800Win.Inject 1kHz at -10dBm into the line input (D-range 1 (PL100) pins 1 & 4; pins 2 & 3shorted; refer to Section 2.2 of Part F).Adjust RV210 (line sensitivity) fully clockwise and key the transmitter by earthingthe Tx-Key line. Using PGM800Win, adjust the value of the “Deviation” EPOTsetting for the current channel to obtain a deviation limit of ±4.7kHz (±3.8kHz)[±2.3kHz] (you can use either the mouse or up and down arrow keys).Sweep the audio frequency from 100Hz to 4kHz and ensure that the maximumdeviation does not exceed ±4.7kHz (±3.8kHz) [±2.3kHz]. Readjust “Deviation” ifnecessary via PGM800Win.3.4.7 Line-in Level AdjustmentRemove the CTCSS signal (if used).Set the injected signal at the line input to the required line level (typically -10 to-20dBm).Adjust RV210 (line sensitivity) to provide ±3kHz (±2.4kHz) [±1.5kHz] deviation.Reapply the CTCSS signal (if required).
C3.8T856/857 Initial Tuning & AdjustmentM850-0031/09/98 Copyright TEL3.5 Audio Processor Links3.5.1 Link DetailsUse the following table to set up the audio processor to the configuration you require.You should set the audio processor links before carrying out any of the tuning andadjustment procedures. The factory settings are shown in brackets [ ].3.5.2 Typical OptionsPlug Linkaa. The letters in this column and in the table in Section 3.5.2 below refer to the identificationletters screen printed onto the PCB beside each pair of pins.FunctionPL2051-2[3-4]5-6ABCnot connectedmicrophone pre-amp. output to compressor inputmicrophone pre-amp. output to multiplexer inputPL210[1-2]3-45-6LMNmultiplexer output to pre-emphasis inputmultiplexer output to limiter inputmultiplexer output to compressor inputPL2151-2[3-4]5-67-89-10GHIJKnot connectedcompressor output to multiplexer inputcompressor output to limiter inputcompressor output to pre-emphasis inputnot connectedPL2201-2[3-4]5-6DEFpre-emphasis output to multiplexer inputpre-emphasis output to limiter inputnot connectedPL205 PL210 PL215 PL220microphone pre-amp. compressedand pre-emphasised;line input pre-emphasised(standard set-up)[3-4]B[1-2]L[3-4]H[3-4]Emicrophone pre-amp. compressedand pre-emphasised;line input unprocessed3-4B3-4M7-8J1-2Dline and microphone compressedand pre-emphasised5-6C5-6N7-8J3-4Emicrophone pre-amp. compressed;line and microphone flat response3-4B3-4M3-4H5-6F
M850-00T856/857 Initial Tuning & AdjustmentC3.9Copyright TEL 31/09/983.6 Synthesiser Alignment• Ensure that the T856/857 has been programmed with the required frequenciesusing PGM800Win software.•Single Channel Select a channel using PGM800Win.Multichannel Select the middle channel via PGM800Win.• Connect a high impedance voltmeter to the long lead of L1 in the VCO (this meas-ures the synthesiser loop voltage).• Key the transmitter by earthing the Tx-Key line.Single Channel Tune VCO trimmer C6 for a synthesiser loop voltage of10V.Multichannel Tune VCO trimmer C6 for a synthesiser loop voltage of10V on the middle channel.If there is no middle channel, tune C6 so that the channelsare symmetrically placed around a loop voltage of 10V.All channels should lie within the upper and lower limitsof 16V and 3V respectively.Do not attempt to program channels with a greater fre-quency separation than the specified switching range(8MHz).• Check that the exciter output power is 1W ±300mW (T857 only).• Measure the exciter output frequency and adjust the TCXO (=IC700) trimmer ifrequired.Caution:This trimmer is susceptible to physical damage. Do not exert a down-ward force of more than 500g (1lb) when adjusting.
C3.10T856/857 Initial Tuning & AdjustmentM850-0031/09/98 Copyright TEL3.7 PA Alignment (T856 Only)Check that the exciter is connected to the PA with the coaxial link.Connect an RF power meter to the PA output (use an appropriate attenuator asnecessary).Turn RV310 (power control) fully clockwise.Note:Before the following measurement is taken, ensure the heatsink is at ambi-ent temperature (20-25°C).Measure and record the voltage (VL) at L481; perform this measurement at roomtemperature so that the NTC (R481) is close to 25°C.Key the transmitter by earthing the Tx-Key line.Tune #CV475 until maximum power is obtained. Check that the power exceeds30W.Adjust RV310 (power control) to 25W.Readjust #CV475 to reduce the supply current by up to 0.5A.3.8 Thermal Shutdown (T856 Only)Key the transmitter by earthing the Tx-Key line and set the output power to 25Was described in Section 3.7.Short L481 to ground.Set RV330 (shutdown power level) for an output power of 5W.Set RV320 (shutdown temperature) to 0.16VL volts (measured at IC350 pin 3),where VL is the voltage measured at L481 in Section 3.7. This sets the thermalshutdown at 85°C at NTC R481.
M850-00T856/857 Initial Tuning & AdjustmentC3.11Copyright TEL 29/02/003.9 Audio Processor & CTCSS3.9.1 Two Point ModulationThe T856 and T857 utilise two point modulation to obtain a wide audio bandwidthindependent of the synthesiser loop filter response. This is achieved by simultaneouslyfrequency modulating the VCO and phase modulating the synthesiser reference fre-quency. The relative signal levels fed to the two modulators are quite critical and causeinteraction when setting up.Both modulating signals require readjustment when the exciter is shifted in frequencygreater than the switching range (i.e. ∆F>±4MHz).Note 1:In this and following sections deviation settings are given first for widebandwidth sets, followed by settings in brackets for mid bandwidth sets ( )and narrow bandwidth sets [ ].Note 2:The reference modulation and limiter adjustments are controlled by 256-step electronic potentiometers (EPOTs), which are adjusted via the “Refer-ence Modulation” and “Deviation” settings in PGM800Win. This allows thetwo point modulation and deviation settings to be adjusted for each chan-nel.Note 3:To optimise the modulation response across the switching range, repeatsteps 1-4 below for each channel that will be used (usually needed only fordata applications). In applications where the modulation response is lesscritical (e.g. voice use only), carry out steps 1-4 below on the middle channeland use the “EPOT Fill” option1 in PGM800Win to copy the value to theother channels.Note 4:If you are using an RF test set, turn the low pass filter off and set the highpass filter to 15kHz before beginning this procedure.3.9.2 Modulator Adjustment1. Inject an audio signal of 300Hz 1.5V rms (+5dBm) into the CTCSS input (D-range1 (PL100) pin 8). Key the transmitter by earthing the Tx-Key line.2. Adjust the output from the audio generator to obtain ±3kHz (±2.4kHz) [±1.5kHz]deviation at 300Hz.3. Change the input frequency to 100Hz and, using PGM800Win, adjust the value ofthe “Reference Modulation” EPOT setting for the current channel to obtain ±3kHz(±2.4kHz) [±1.5kHz] deviation (you can use either the mouse or up and downarrow keys).1. Use the “EDIT FILL” button on the tool bar or go to “Edit”, “Fill”, “Epot Settings” on the menu bar.
C3.12T856/857 Initial Tuning & AdjustmentM850-0029/02/00 Copyright TEL4. Change the input frequency back to 300Hz.Repeat steps 2 and 3 above until the deviations achieved at the two input frequen-cies are within 0.2dB of each other. You will need to do this at least four times.5. Sweep the audio between 50 and 300Hz for peaks.Note:A peak between 50 and 300Hz will indicate a fault condition, i.e:- incorrect set-up or - modulation circuitry fault. The specification window is ±1dB relative to 150Hz from 67 to 260Hz.3.9.3 CTCSS Encoder (If Used)Program a CTCSS tone on the default channel using PGM800Win.If you are using an RF test set, turn off the 300Hz high pass filter.Key the T856/857 with the front panel "Carrier" switch.Adjust RV805 (CTCSS level adjust) to give ±500Hz (±350Hz) [±250Hz] deviation.Set the maximum deviation as per Section 3.9.4.3.9.4 Limiter AdjustmentNote:If the T856/857 will be used over the whole 8MHz switching range, youmust set the deviation for each channel. However, if the module will beused on frequencies that cover only a 1MHz (or less) switching range, youcan set the deviation on the middle channel and use this value for all otherchannels with the “EPOT Fill” option in PGM800Win.Set the links in the audio processor section as required (refer to Section 3.5).Inject 1kHz at -10dBm into the line input (D-range 1 (PL100) pins 1 & 4; and pins 2& 3 shorted; refer to Section 2.2 of Part F).Adjust RV210 (line sensitivity) fully clockwise and key the transmitter by earthingthe Tx-Key line. Using PGM800Win, adjust the value of the “Deviation” EPOTsetting for the current channel to obtain a deviation limit of ±4.7kHz (±3.8kHz)[±2.3kHz] (you can use either the mouse or up and down arrow keys).Sweep the audio frequency from 100Hz to 4kHz and ensure that the maximumdeviation does not exceed ±4.7kHz (±3.8kHz) [±2.3kHz]. Readjust “Deviation” ifnecessary via PGM800Win.
M850-00T856/857 Initial Tuning & AdjustmentC3.13Copyright TEL 29/02/003.9.5 Line Level Without CompressorThis section assumes that the compressor is not used. If the compressor is required,refer to Section 3.9.6.Remove the CTCSS signal (if used).Adjust the line sensitivity as follows: • set the injected signal at the line input to the required line level (typically -10 to-20dBm);• adjust RV210 (line sensitivity) to provide ±3kHz (±2.4kHz) [±1.5kHz] devia-tion.Reapply the CTCSS signal (if required).3.9.6 CompressorThe compressor may be used on the line input only, the microphone input only, or onboth the line and microphone inputs. If the compressor is used, refer to one of the fol-lowing sections as appropriate.3.9.6.1 Compressor On Line Input OnlySet RV210 (line sensitivity) fully clockwise and key the transmitter by earthing theTx-Key line.Reduce the line level to -50dBm at 1kHz and set RV220 (compression level) fullyclockwise.Check that ±3kHz deviation (±2.4kHz) [±1.5kHz] is still available.Slowly increase the audio input level until the demodulated waveform shows sig-nificant signs of clipping (approximately ±4.5kHz (±3.6kHz) [±2.3kHz] deviation).Adjust RV220 anticlockwise until the demodulated waveform is just clipping(approximately ±4kHz (±3.2kHz) [±2kHz] deviation).Increase the input level to -10dBm and check that the test tone is still held just intoclipping. The input line level should be typically -10 to -20dBm.3.9.6.2 Compressor On Microphone Input OnlyKey the transmitter by earthing the Tx-Key line and plug a microphone jack intothe front panel socket.Adjust RV220 (compression level) fully clockwise.Acoustically couple the microphone to a tone box (1kHz) and close the PTTswitch.
C3.14T856/857 Initial Tuning & AdjustmentM850-0029/02/00 Copyright TELIncrease the audio level until the demodulated waveform shows significant signsof clipping (approximately ±4.5kHz (±3.6kHz) [±2.3kHz] deviation).Adjust RV220 anticlockwise until the demodulated waveform is just clipping(approximately ±4kHz (±3.2khz) [±2kHz] deviation).Increase the audio level by 10dB and verify that the test tone is held just into clip-ping.Whistle steadily into the microphone, checking that approximately ±4kHz(±3.2khz) [±2kHz] deviation is produced. The modulated waveform should bebasically sinusoidal.Speak into the microphone, checking that the modulation peaks reach about±5kHz (±4kHz) [±2.5kHz] deviation.As the line is to be used without compression, set RV210 (line sensitivity) asdescribed in Section 3.9.5.3.9.6.3 Compressor On Both Line & Microphone InputsSet up as described in Section 3.9.6.1.
M850-00T856/857 Functional TestingC4.1Copyright TEL 31/09/984 T856/857 Functional TestingCaution:This equipment contains CMOS devices which are susceptible to dam-age from static charges. Refer to Section 1.2 in Part A for more infor-mation on anti-static procedures when handling these devices.The following test procedures will confirm that the T856/857 has been tuned andadjusted correctly and is fully operational.Note 1:In this and following sections deviation settings are given first for widebandwidth sets, followed by settings in brackets for mid bandwidth sets ( )and narrow bandwidth sets [ ].Note 2:Unless otherwise specified, the term "PGM800Win" used in this and follow-ing sections refers to version 2.00 and later of the software.Refer to Figure 4.4 and Figure 4.5 for the location of the main tuning and adjustmentcontrols, and to Section 3.3 for the test equipment set-up. Refer also to Section 6 wherethe parts lists, grid reference index and diagrams will provide detailed information onidentifying and locating components and test points on the main PCB. The parts listand diagrams for the VCO PCB are in Part E.The following topics are covered in this section.Section Title Page4.1 Current Consumption 4.34.2 Output Power 4.34.3 Output Frequency 4.34.4 Timers 4.34.5 Frequency Response 4.44.6 Audio Level Input Sensitivity 4.7Figure Title Page4.14.24.34.44.5T856/857 Transmit TimersT856/857 Pre-emphasis ResponseT856/857 Limiting ResponseT856 Main Tuning & Adjustment ControlsT857 Main Tuning & Adjustment Controls4.44.54.64.94.11
C4.2T856/857 Functional TestingM850-0031/09/98 Copyright TEL
M850-00T856/857 Functional TestingC4.3Copyright TEL 31/09/984.1 Current ConsumptionConnect the T856/857 to a 13.8V power supply.Connect an RF power meter to the T856/857 output socket.Check that the current in the 13.8V power cable is less than 150mA.Key the T856/857 by earthing the Tx-Key line (the carrier "On" LED should light).T856 Only: Adjust RV310 (power control) to obtain 25W output power.Check that the current is as follows:T856 <5.5AT857 <750mA.4.2 Output PowerConnect an RF power meter with suitable attenuation to the T856/857 outputsocket.Key the T856/857 by earthing the Tx-Key line.Check that:T856 the output power adjusts to ≥25W with RV310 (power control)turned fully clockwiseT857 the output power is 1W ±300mW.4.3 Output FrequencyConnect the T856/857 output to a frequency counter via an attenuator pad:T856 40dB padT857 20dB pad.Measure the output frequency and, if necessary, adjust the TCXO (=IC700) to trimto the nominal frequency (±100Hz).4.4 TimersThe transmit tail timer, transmit timeout timer and transmit lockout timer can allbe set from PGM800Win. The fields for setting these are found on the systeminformation page. These three timers operate as follows (refer also to Figure 4.1):
C4.4T856/857 Functional TestingM850-0029/02/00 Copyright TELFigure 4.1 T856/857 Transmit Timers4.5 Frequency ResponseIf the T856/857 has been correctly adjusted, the pre-emphasis and limiting responsesshould closely match those shown in Figure 4.2 and Figure 4.3 respectively. Note:The limits shown on these graphs should not be exceeded. • If you are using an RF test set, turn off all filters.• Measure the pre-emphasis response as follows: Reduce the line level to give ±1kHz (±0.8kHz) [±0.5kHz] deviation at 1kHz. Sweep the modulation frequency. The response should closely match that shown in Figure 4.2.• Measure the limiting response as follows: Set the line level to give ±3kHz (±2.4kHz) [±1.5kHz] deviation at 1kHz. Timer Function AdjustmentTransmit Tail Sets the tail time during which the transmitter stays keyed after the exter-nal key source has been removed.0-5 seconds in 100ms stepsaa. Adjustable in 20ms steps in PGM800Win version 2.12 and later.Transmit Timeout Sets the maximum continuous trans-mission time. Once the timer has timed out, the transmitter must be keyed again, unless prevented by the transmit lockout timer.0-300 secondsb in 10 second stepsb. Adjustable in 20ms steps in PGM800Win version 2.12 and later.Transmit Lockout Sets the period of time that must elapse after a timeout before the trans-mitter can re-transmit. Once the timer has timed out, the transmitter can be keyed again.0-60 seconds in 10 second stepsOnLockout TimeTimeoutTimeOnTail TimeTx-EnableTx-Reg.Tx-EnableTx-Reg.
M850-00T856/857 Functional TestingC4.5Copyright TEL 29/02/00Increase the line level 20dB and sweep the modulation frequency. The response should closely match that shown in Figure 4.3.Figure 4.2 T856/857 Pre-emphasis ResponseWide BandwidthNarrow BandwidthMid BandwidthThe mid bandwidth graph is the same shape as the wide bandwidth graph. The devia-tion figures are as follows:peak + max. deviation = +0.8kHzpeak - max. deviation = -0.8kHz.+10+8Modulation Level (dB ref. to dev. @ 1kHz)+6+4+2+0-2-4-6-8-10-12-14-16-18-20-22100 200 300 500 1k 2k 3k 5k 10kFrequency (Hz)Peak + max. dev. = +1.0kHz @ 1000HzPeak - max. dev. = -1.0kHz @ 1000Hz+10+8Modulation Level (dB ref. to dev. @ 1kHz)+6+4+2+0-2-4-6-8-10-12-14-16-18-20-22100 200 300 500 1k 2k 3k 5k 10kFrequency (Hz)Peak + max. dev. = +0.5kHz @ 1000HzPeak - max. dev. = -0.5kHz @ 1000Hz
C4.6T856/857 Functional TestingM850-0031/09/98 Copyright TELFigure 4.3 T856/857 Limiting ResponseWide BandwidthNarrow Bandwidth100 500300 5k50+10+8Modulation Level (dB ref. to max. dev.)+6+4+2+0-2-4-6-8-10-12-14-16-18-20-2210 20 30 200 1k 2k 3k 10kFrequency (Hz)Peak + max. dev. = +4.9kHz @ 1500HzPeak - max. dev. = -4.4kHz @ 2500HzAbove limiting (steady-state)Mid BandwidthThe mid bandwidth graph is the same shape as the wide bandwidth graph. The devia-tion figures are as follows:peak + max. deviation = +4kHzpeak - max. deviation = -4kHz.100 500300 5k50+10+8Modulation Level (dB ref. to max. dev.)+6+4+2+0-2-4-6-8-10-12-14-16-18-20-2210 20 30 200 1k 2k 3k 10kFrequency (Hz)Peak + max. dev. = +2.4kHz @ 2000HzPeak - max. dev. = -2.5kHz @ 2000HzAbove limiting (steady-state)
M850-00T856/857 Functional TestingC4.7Copyright TEL 31/09/984.6 Audio Level Input Sensitivity• Adjust RV210 (line sensitivity) fully clockwise.• Check that the input sensitivities are better than those specified below:Note:A degraded signal to noise ratio can be expected with the compressorselected. The extent of the degradation is dependent on the audio inputlevel.Line Input 600 ohms, ±3kHz (±2.4kHz) [±1.5kHz] deviation at 1kHz: with compressor -50dBm without compressor -30dBmMicrophone Input 600 ohms, ±3kHz (±2.4kHz) [±1.5kHz] deviation at 1kHz: with compressor -75dBm without compressor -55dBmCTCSS Input 1kHz deviation at 150Hz 500mV rms
C4.8T856/857 Functional TestingM850-0031/09/98 Copyright TEL
M850-00T856/857 Fault FindingC5.1Copyright TEL 31/09/985 T856/857 Fault FindingCaution:This equipment contains CMOS devices which are susceptible to dam-age from static charges. Refer to Section 1.2 in Part A for more infor-mation on anti-static procedures when handling these devices.The following test procedures and fault finding flow charts may be used to help locate ahardware problem, however they are by no means a complete fault finding procedure.If you still cannot trace the fault after progressing through them in a logical manner,contact your nearest Tait Dealer or Customer Service Organisation. If necessary, youcan get additional technical help from Customer Support, Radio Systems Division, TaitElectronics Ltd, Christchurch, New Zealand (full contact details are on page 2).Note 1:In this and following sections deviation settings are given first for widebandwidth sets, followed by settings in brackets for mid bandwidth sets ( )and narrow bandwidth sets [ ].Note 2:Unless otherwise specified, the term "PGM800Win" used in this and follow-ing sections refers to version 2.00 and later of the software.Refer to Section 6 where the parts lists, grid reference index and diagrams will providedetailed information on identifying and locating components and test points on themain PCB. The parts list and diagrams for the VCO PCB are in Part E.The following topics are covered in this sectionSection Title Page5.1 Visual Checks 5.35.2 Component Checks 5.35.3 Front Panel LED Indicator 5.35.45.4.15.4.2DC ChecksPower RailsVCO Locking5.45.45.45.55.5.15.5.25.5.35.5.4RF ChecksT856 Drive PowerT856 PA Output PowerT857 Output PowerAudio And Modulation5.55.55.55.55.65.6 PGM800Win Generated Errors 5.7
C5.2T856/857 Fault FindingM850-0031/09/98 Copyright TEL5.75.7.15.7.1.15.7.1.25.7.1.35.7.25.7.35.7.45.7.55.7.65.7.7Fault Finding ChartsMicrocontrollerBasic ChecksSerial CommunicationsCTCSS EncodeRegulatorSynthesiserT856 Drive AmplifierT856 PA & Power ControlT857 Exciter Drive AmplifierAudio Processor5.85.85.85.95.105.115.125.155.165.175.185.8 To Replace The T856 PA Transistors (Q410 & Q420) 5.19Figure Title Page5.15.2RF Diode Probe CircuitTypical Transistor/Capacitor Spacing (Not To Scale)5.55.19Section Title Page
M850-00T856/857 Fault FindingC5.3Copyright TEL 31/09/985.1 Visual ChecksRemove the covers from the T856/857 and inspect the PCB for damaged or broken com-ponents, paying particular attention to the surface mounted devices (SMD's).Check for defective solder joints. If repair or replacement is considered necessary, referto Section 3 of Part A.5.2 Component ChecksIf you suspect a transistor is faulty, you can assess its performance by measuring the for-ward and reverse resistance of the junctions. Unless the device is completely desol-dered, first make sure that the transistor is not shunted by some circuit resistance. Use agood quality EVM (e.g. Fluke 75) for taking the measurements (or a 20k ohm/V or bet-ter multimeter, using only the medium or low resistance ranges).The collector current drawn by multi-junction transistors is a further guide to their per-formance.If an IC is suspect, the most reliable check is to measure the DC operating voltages. Dueto the catastrophic nature of most IC failures, the pin voltages will usually be markedlydifferent from the recommended values in the presence of a fault. The recommendedvalues can be obtained from either the circuit diagram or the component data catalogue.5.3 Front Panel LED IndicatorThe green "Supply" LED on the T856/857 front panel will flash according to the condi-tions described in the following table:Where two or more conditions occur at the same time, the precedence is in the ordershown above (i.e. T856/857 linked has the highest priority, followed by internal error).Flash Rate Conditionfast ( sec. on/ sec. off approx.) T856/857 is linked with PGM800Winunequal ( sec. on/1 sec. off approx.) microcontroller has detected an internal communications error -refer to Section 5.7.1
C5.4T856/857 Fault FindingM850-0031/09/98 Copyright TEL5.4 DC Checks5.4.1 Power RailsRefer to the test points and options diagrams in Section 6 for test point locations, and tothe regulator fault finding chart (Section 5.7.2) for fault diagnosis.Check the 13.8V (TP601) and 9V (TP602) supplies at their test points in the regula-tor compartment with a DMM.Check the 5V (TP604) and 20V (TP603) rails at their respective test points in theregulator compartment.Check that Tx-Reg. (TP305 in the exciter compartment) comes up to 8.8V when theexciter is keyed.Check the +5V digital regulator output (TP607 in the regulator compartment).T856 Only: Check the 9V supply (IC370 pin 1) with a DMM.Check for short circuits.5.4.2 VCO LockingKey the exciter.Using a DMM, monitor the VCO control voltage on the long lead of L1 on theVCO PCB.If the synthesiser is locked and the VCO aligned, the voltage at this point shouldbe between 3 and 16V.If the VCO is not locked, refer to the synthesiser fault finding chart (Section 5.7.3).
M850-00T856/857 Fault FindingC5.5Copyright TEL 31/09/985.5 RF ChecksIn-circuit RF levels may be measured with an RF probe on which the earth lead has beenshortened to a minimum (i.e. 13mm). Refer to the circuit diagrams for typical levels. Figure 5.1 shows a suitable RF probe circuit..Figure 5.1 RF Diode Probe Circuit5.5.1 T856 Drive PowerRefer to the drive amplifier fault finding chart (Section 5.7.4).Ensure that the VCO locks (refer to Section 5.4.2).Connect the drive output to a power meter and key the transmitter.Check that the exciter output power (SK310) is >1.5W.Note:If the synthesiser is out of lock, the lock detector (synthesiser IC740 andcomparator IC750) will prevent the RF signal from reaching the PA byswitching the supply to the exciter amplifier (Q350, Q355).5.5.2 T856 PA Output PowerReconnect the drive output to the PA input.Connect the PA to a power meter and key the transmitter.Check that the output power is >30W with RV310 (power control) adjusted fullyclockwise.5.5.3 T857 Output PowerRefer to the exciter drive amplifier fault finding chart (Section 5.7.6).Ensure that the VCO locks (refer to Section 5.4.2).100k10k1n1n1N6263CoaxProbeEarthing ClipDC to DVM orOscilloscopeThis unit is not suitable for use on high power RF circuits.
C5.6T856/857 Fault FindingM850-0031/09/98 Copyright TELConnect the exciter output to a power meter and key the exciter.Check that the output power is 1W ±300mW.Note:If the synthesiser is out of lock, the lock detector (synthesiser IC740 andcomparator IC750) will prevent the RF signal from reaching the PA byswitching the supply to the exciter amplifier (Q301, IC300, Q302, Q303).5.5.4 Audio And ModulationRefer to the audio processor fault finding chart (Section 5.7.7).Set up the audio processor as described in Section 3.9.Check that the demodulated RF output has the frequency response referred to inSection 4.5 with at least ±5kHz (±4kHz) [±2.5kHz] deviation available at 1kHzmodulating frequency.If the above result is not achieved, either the two modulators are incorrectly adjusted ora fault condition exists.
M850-00T856/857 Fault FindingC5.7Copyright TEL 31/09/985.6 PGM800Win Generated ErrorsThe following errors are those most likely to occur using PGM800Win. Refer to thePGM800Win software user’s manual for a complete list of error messages.Channel Switch SetThe programmed default channel change was not accepted by the base station because achannel is selected externally. Try turning the external channel switch off to change thedefault channel in PGM800Win.Synth Out Of LockThe synthesiser received incorrect data, or the data was corrupted. Enter a frequencywithin the VCO switching range, or tune the VCO.Internal ErrorData could not be read from the base station due to an internal error. Check for shortsor open circuits on the SDA, SCK, SYNTH and EPOT lines. The SDA, SCK and SYNTHare normally high, and the EPOT is normally low.Write/Read To An Unlinked ModuleThe link to the module does not exist. Undefined error.
C5.8T856/857 Fault FindingM850-0031/09/98 Copyright TEL5.7 Fault Finding ChartsNote:The standard test point designations used in this section are as follows:TP601 13.8VTP602 9VTP603 20VTP604 5V5.7.1 Microcontroller (IC810)5.7.1.1 Basic ChecksPulsing Check state of pin 35.YIs pin 30 pulsing?High or open circuitYStatic high/lowCheck state ofpins 36 to 43.Low/floatingHighIs the 12.8MHz clockpresent on IC810 pin 21 (microcontroller)?NReplaceIC810.Check IC740(synthesiser).*digital storage oscilloscopeReplace IC810.Check thestate ofpin 10.N PulsingLowReplaceIC810.Use a DSO* to checkoperation of IC650(i.e. active high pulse at power up).ReplaceIC650.Correct the fault causingpin 35 to be low/floating.
M850-00T856/857 Fault FindingC5.9Copyright TEL 31/09/985.7.1.2 Serial CommunicationCheck pin state.YLow/floatingNNoise on pinDisconnect theprogramming lead.Is IC810 pin 11 high?(microcontroller)Y*digital storageoscilloscopeUse PGM800Winto send a POLL command to theradio.Check the transistorinterface circuitryand/or replace theprogramming lead.Check the SERIAL-COMand AUDIO-1/2 links.ReplaceIC810.Check the transistorinterface circuitryand/or replace theprogramming lead.Check the transistorinterface circuitry.Check IC810 pin 13with a DSO. Is therea response from IC810 aftera poll command is sent?NYConnect the programminglead and use PGM800Winto read the rack/radio.Check I/O pad P810with a DSO*.Does it swing from0 to 5V?N
C5.10T856/857 Fault FindingM850-0031/09/98 Copyright TEL5.7.1.3 CTCSS EncodeYYYReplace IC810.Use PGM800Win toselect a channelwith a CTCSS toneprogrammed.Check serial communications.(See separate flow chart).Cannot select a channelCheck IC810 pins 24, 25& 26 (microcontroller).Are there 5V square waves atthe CTCSS frequency?Check IC830 pins 1, 7 & 14.Are there 9V square waves atthe CTCSS frequency?Check IC830 pin 8.Is there a sine waveat the CTCSS frequency? Check RV805.No toneCheck the filter circuit for biasproblems and/or short circuits.Distorted toneNo square waves oruneven mark/space ratioNo square waves oruneven mark/space ratio Check IC830 circuitryand repair/replace.
M850-00T856/857 Fault FindingC5.11Copyright TEL 31/09/985.7.2 RegulatorNYCheck foroverheatingcomponents &short circuits.NYCheck Q630,Q620 & IC640.NY9.0V presenton TP602?Check Q660 isswitching atapprox. 150kHz.NY20V presenton TP603?Check R615.Replace IC610.NY+5V present onIC610 pin 2?Key Tx.YRegulators OK.N8.8V presenton Tx reg. TP305?Replace Q610.YN0V presenton Q860 collector?Check Q860 andassociated circuitry.Y0.6V present onQ860 base?NRegulators OK.Check microcontrollersection.Check continuityfrom pin 9 ofD-range 1.13.8V present onIC630 pin 3?5.3V present onIC630 pin 1? Replace IC630.
C5.12T856/857 Fault FindingM850-0031/09/98 Copyright TEL5.7.3 SynthesiserRefer to the synthesiser circuit diagram (sheet 7) in Section 6 and the VCO circuit dia-gram in Part E.N A BCheck biasingresistors, Q4 & Q5.NYN8.3V presentat VCO?DC V presentat Q4 & Q5?9V present atVCO Q4/Q5?No VCO RF output.YDC V present atVCO, Q1, Q2 & Q3?Check biasingresistors, Q1,Q2 & Q3.YNCapacitors OK?Check for cracks,shorts, etc.NYReplace VCO.Replaceif faulty.YNYNNNYYDC V presenton Q795 emitter?Check 9V supply.9V present onQ795 divider buffer?20V invertersupply faulty.20V presenton IC750 pin 8?Check 5V reg. &supply resistorto each IC.+5V present atIC700, IC710,IC740, IC720& IC730?VCO out of lock.YYYContinued on the next pageYVCO freq. correct?Synthesiser OK.VCO trimmerfreq. range OK?Check VCO tuningcaps & trimmer.VCO OK.NNNNNYYRecheckprogrammingvia PGM800Win.Check Q5 Cmultiplier(synth).Check biasingresistors & Q795.Check Tx reg.,Q610 & 9V reg.Does VCO trimmeradjust for stablecontrol linebetween 3 & 16V?Does VCO trimmeradjust for requiredfrequency rangebetween 3 & 16V?Check #C1, #C7, #C8,C6 & D1-D2 in VCO.Is 8MHz VCO rangeachieved between3 & 16V?
M850-00T856/857 Fault FindingC5.13Copyright TEL 31/09/98Programming and serial bus OK?Check programming.Check serial buswhen programmingi.e. clock/data/enable activity (IC740 pins18, 19 & 17). NCheck loop filter componentsR775, C774, C776, R510,C505, IC750. Is the supplyto IC750 +20V +4, -2V?Check regulator circuitry.Check C772, R774, R772,C770, R763 & Q790.Check Q760, Q780,R766 & C765.Check charge pump components(Q775 & Q780) and Q790. Check R762 & C762.Check the signal path from the VCO to synthesiser. Measure the frequency fromthe VCO at IC740 pin 11 usinga frequency counter.Is the level >-10dBm?Does the frequency adjustas the VCO trimmer is adjusted (out of lock)?Check VCO.YYYSignalYYYNo signalReplace synthesiser(IC740).YN YYNNNNCheck phase detector outputpins (IC740 pins 3 & 4).Are there very narrow pulses(~50ns) at the reference frequency?(i.e. 5kHz : 200µs period 6.25kHz : 160µs period)*See Note below.Is the charge pump biasvoltage at the base of Q760 & Q780 between 3.5 and 5V? (5V when locked)NIs the voltage on C762,R760, and R758 9V ±0.2V?Is the loop filter reference voltage at C772 (+) 6.5V ±0.2V?NCheck divider buffercircuit (Q795) and biasvoltages on Q795 emitter(1.3V ±0.2V).*Note:When locked, both of theseare very narrow (~50ns).If unlocked, one will bevery narrow (~50ns),and the other wide (>15µs).Replace synthesiser(IC740).Continued from previous page BIs the charge pump voltageon Q790 gate between 3 and 8.5V? (6.5V ±0.2V locked)Is referenceclock presentat IC740 pin 20(200kHz >4.5Vpp)?Check microcontrollersection (IC810).NIs referenceclock presentat IC730 pin 12(200kHz >4.5Vpp)?Is referenceclock presentat IC730 pin 1(12.8MHz >4.0Vpp)?Check TCXO (IC700)and buffers (IC710).NNYYCheck phasemodulator sections:IC720, Q710, Q720,D710, Q730, Q740,D720.Check dividerIC730.
C5.14T856/857 Fault FindingM850-0031/09/98 Copyright TELYNYYCorrect DC Vpresent on Q1 VCO?NCheck inductors,biasing resistors& Q1.Replace if faulty.Go to B.Loop filter &components aroundop. amp. (IC750) OK?NNoisy synth;poor residual FM. CIsolate audiomodulation on VCO;still noisy? Trace audio fault.YYNYYYChange trimmer;still noisy?Change Q1;still noisy?Change TCXO;still noisy?Change varactors;still noisy?Replace VCOassembly.Synthesiser OK.NNNNYVCO phase locked?3-16V present oncontrol line?
M850-00T856/857 Fault FindingC5.15Copyright TEL 31/09/985.7.4 T856 Drive Amplifier10.5V on Q315collector?Check continuityof power rails& DC paths toQ365 & Q370.Check signalpath to outputincl. outputsocket (SK310).Key exciter& locksynthesiser.NNYYYCheck VCO.NYYNYYNYNYCheck 9V &13.8V supplies.Checkregulators.Check temp.shutdowncircuit.NYNYNY10.5V on Q350collector?10.5V on Q355collector?13.8V onIC350 pin 8?11.5V onIC350 pin 7?NCheck lock det.path back tosynth. IC740,IC750, Q325.Check TP305>+8V.Check TP320<0.6V.Check Q310,Q315 circuitry& IC350.>2V RF atVCO output?>1V RFat R381?NCheck attenuatorpad #R517, #R518,#R519.>0.5V RF atQ350 base?Check C355, C358,C360, Q350, D340,D380, D360, L320.NCheck Q350.>1V RF atQ355 base?Check signalpath betweenQ350 & Q355.>6V RF atQ355 collector? Check Q355.>5V RF atC362, #R395?
C5.16T856/857 Fault FindingM850-0031/09/98 Copyright TEL5.7.5 T856 PA & Power ControlCheck IC330,Q310, Q315& circuitry,+13.8V supply.Refer to Drive Amp.Fault Finding Chart. Check supplycircuitry.Tx deliveringfull power(>30W)?Set RV320(power adjust)fully clockwise;synth. locked;key Tx.YNYNNYNYNNYYYYPower controlcircuitry OK.Note:c/w = clockwisecc/w = counterclockwise or anticlockwiseCheck Q410,Q420 & circuitry,LP filter.10.8Vat L310? Check drive atSK310 >1.5W. Check +13.8V atQ410 & Q420.<2V onIC350 pin 6?Turn RV310 ccw.Check powerdrops to zeroslowly in a controlled manner.Does variationof RV310cause eitherfull poweror no power?Check for breakin power sensecircuitry; directionalcoupler D420,D440 & circuitry.Set RV310 so thatoutput power = 25W;check L310 approx. 7.5V.Momentarily removeTx load. Voltage atL310 decreases toapprox. 5V?Check lock det. circuit;TP305 should be >8V.Check temp. shutdowncircuit (IC350);TP320 should be <0.6V.Check Q320, RV330.Normal operating conditions:Forward power = 4.7V approx.Reverse power = 0.7V approx.IC350 pin 6 = 2.02VIC350 pin 5 = 2VIC350 pin 7 = 8.63V
M850-00T856/857 Fault FindingC5.17Copyright TEL 31/09/985.7.6 T857 Exciter Drive AmplifierCheckpower rails.Check VCO.Drive amp. OK.NNYYNYYNYNY9V at Q304 collector?0.5V at Q304 base?9V at Q305 collector?Key exciter &lock synthesiser.YN9V at Q303collector?Y>4V present onIC300 pin 1? Check IC300.Check Q302& Q303.>2V RF atVCO output?N>1V RF at R323? NYCheck attenuator padR517, R518, R519.>0.5V RF atQ304 base?Check C314, #C315,#C316, Q304, L305,D201, D202, D203.>5V RF at#C321, #R330?NCheck Q304.>1V RF atQ305 base? Check signal pathbetween Q304 & Q305.>5V RF atQ305 collector? Check Q305.
C5.18T856/857 Fault FindingM850-0031/09/98 Copyright TEL5.7.7 Audio ProcessorNIC240 pin 6at 9V?Key exciter &lock synthesiser.Connect 1kHz audioto external CTCSS input.Does excitermodulate? Audio output atIC260 pin 8?NYCheck audio path toVCO control line.Check alignmentof modulators.YNAudio output atIC260 pin 1?YCheck buffer IC260pins 8, 9 & 10.NAudio output atIC260 pin 7?Check low passfilter stage IC260pins 1, 2 & 3.YCheck stage IC260pins 5, 6 & 7.NDemodulated audiofrequency responseflat between 50 & 300Hz?YCheck lowpass filterstage IC260pins 1, 2 & 3.NNYAudio frequencyresponse IC260pin 1 flat 300Hzto 2kHz?Audio frequencyresponse IC210pin 8 6dB/octaveslope?Check integratorIC210 pins 8, 9, & 10.NYAudio superimposedon 200kHz signalIC720 pins 9 & 3 (synth)?Check audio pathbetween integrator& phase modulator.NY200kHz clippedtriangle wave atIC720 pins 8 & 4?Check IC720, Q710, Q720, Q730, Q740, D710, D720, C727, C729, C724 & C725NYCheck loop filter (IC750, pins 5, 6 & 7)& associatedcomponents.Select standardaudio configuration.Check pre-emphasisnetwork IC230 pins 12,13 & 14 &/or low passfilter IC260 pins 1, 2 & 3.NYConnect audioto line input;key exciter.Does excitermodulate?YNDemodulatedaudio frequencyresponse as perSection 4.5?Audio processorOK.Audio signal atIC210 pin 14?YNAudio signal atIC230 pin 1?NAudio signal atIC230 pin 14?YNAudio signal atIC240 pin 4?YNYCheck Q260 is not faulty orbeing turned on inadvertently.YCheck audio path betweenlimiter IC210 pin 14 &summing amp. IC260 pin 7.Check IC210pins 12, 13 & 14.Check IC230 pins 1, 2 & 3 oraudio path between pre-emphasis network & limiter.Check IC230 pins 12, 13 & 14or audio path between multiplexer& pre-emphasis network.Check IC240 or audiopath between line trans-former & multiplexer.
M850-00T856/857 Fault FindingC5.19Copyright TEL 31/09/985.8 To Replace The T856 PA Transistors(Q410 & Q420)Caution:Failure to comply with the following procedure can result in failure ofthe device due to poor heatsinking, or worse, can endanger the healthof the assembler if the beryllium oxide die carrier is smashed duringassembly.Caution:As the location of certain components in the PA is critical to perform-ance, it is important that any components removed or disturbed arerefitted in exactly the same position.Before attempting to remove a transistor, measure the distancebetween the capacitors and transistor body to the nearest 0.5mm (meas-urement "A" in Figure 5.2) so that the capacitors can be replaced inexactly the same position. These measurements are shown in Figure5.2 for the 6LFL package, however the same procedure applies for theSOE (stud) package.Caution:Do not apply too much heat or pressure to the PCB pads and tracks asyou may damage them or lift them from the PCB, causing permanentdamage to the transmitter.Figure 5.2 Typical Transistor/Capacitor Spacing (Not To Scale)Desolder and remove the components from around the transistor.Q420 Only: Desolder and remove the two solder tags.Desolder the transistor tabs by heating with a soldering iron and lifting awayfrom the PCB with a screwdriver or thin stainless steel spike, then remove thedevice. base collectormeasurement A
C5.20T856/857 Fault FindingM850-0029/02/00 Copyright TELQ410 Only: Unscrew the transistor stud nut and remove the device.Remove any excess solder from the PCB pads with solder wick.Trim the tabs of the replacement transistor so that the device sits neatly on thePCB pads provided.Lightly tin the underside of the transistor tabs. Remove any excess solder to leavea thin, even layer on the tabs.Apply a small amount of heatsink compound (Dow-Corning 340 or equivalent) tothe transistor mounting surface. Sufficient compound should be used to ensurean even film over the entire mounting surface.Place the transistor on the PCB in the correct orientation and ensure the tabs areflush to the surface. Q410 Only: Lightly solder one tab to the PCB, then torque down the retain-ing nut to the correct torque (0.7Nm/6in.lbf.).Caution:Do not solder all the tabs before torquing down otherwise the devicemay be broken.Q420 Only: Refit the solder tags. Solder all transistor tabs to the PCB.Replace each component in exactly the same position as noted previously.
M850-00T856/857 PCB InformationC6.1.1Copyright TEL 29/02/006 T856/857 PCB InformationCaution:This equipment contains CMOS devices which are susceptible to damage fromstatic charges. Refer to Section 1.2 in Part A for more information on anti-staticprocedures when handling these devices.This section provides the following information on the T856 transmitter and T857 exciter:•parts lists• grid reference indexes• mechanical assembly drawings•PCB layouts• test points & options connections drawings• circuit diagrams.Section Title IPN Page6.1 Introduction 6.1.36.2 T856 Transmitter PCB 220-01397-01 6.2.16.3 T857 Exciter PCB 220-01398-02220-01398-046.3.16.3.29
C6.1.2T856/857 PCB InformationM850-0031/09/98 Copyright TEL
M850-00T856/857 PCB InformationC6.1.3Copyright TEL 31/09/986.1 IntroductionProduct Type IdentificationYou can identify the transmitter or exciter type by checking the product code printed on a label onthe rear of the chassis (product codes are explained in Section 1.3 in this Part of the manual, and Fig-ure 1.1 in Part A shows typical labels). You can further verify the product type by checking theplacement of an SMD resistor in the table that is screen printed onto the top side of the PCB, similarto the example drawn below. In this example, the resistor indicates that the product was built as aT856-10-XXXX. Note:The only function of this resistor is to indicate the product type. It has no effect on thecircuitry or operation of the transmitter or exciter.PCB IdentificationAll PCBs are identified by a unique 10 digit “internal part number” (IPN), e.g. 220-01390-02, whichis screen printed onto the PCB (usually on the top side), as shown in the example below:The last 2 digits of this number define the issue status, which starts at 00 and increments through 01,02, 03, etc. as the PCB is updated. Some issue PCBs never reach full production status and are there-fore not included in this manual. A letter following the 10 digit IPN has no relevance in identifyingthe PCB for service purposes.Note:It is important that you identify which issue PCB you are working on so that you canrefer to the appropriate set of PCB information.856-30 PRODUCT TYPE856-35 856-10 856-20856- 856-13 856-23PRODUCT TYPE 856-15 856-25
C6.1.4T856/857 PCB InformationM850-0031/09/98 Copyright TELParts ListsThe 10 digit numbers (000-00000-00) in this Parts List are “internal part numbers” (IPNs). We canprocess your spare parts orders more efficiently and accurately if you quote the IPN and provide abrief description of the part.The components listed in this parts list are divided into two main types: those with a circuit refer-ence (e.g. C2, D1, R121, etc.) and those without (miscellaneous and mechanical).Those with a circuit reference are grouped in alphabetical order and then in numerical order withineach group. Each component entry comprises three or four columns, as shown below:The miscellaneous and mechanical section lists the variant and common parts in IPN order.Parts List AmendmentsAt the front of the parts list is the Parts List Amendments box (an example of which is shownbelow). This box contains a list of component changes which took place after the parts list and dia-grams in this section were compiled. These changes (e.g. value changes, added/deleted compo-nents, etc.) are listed by circuit reference in alphanumeric order and supersede the informationgiven in the parts list or diagrams. Components without circuit references are listed in IPN order.The number in brackets at the end of each entry refers to the Tait internal Change Order document.circuit reference -lists componentsin alphanumericordervariant column -indicates that this isa variant componentwhich is fitted only tothe product type listedInternal Part Number -order the componentby this numberdescription -gives a brief descriptionof the componentParts List AmendmentsR306 Changed from 180Ωto 560Ω(036-13560-00) to increase sensitivity (71003).circuit referenceor IPN descriptionof changeIPN of newcomponent Change Ordernumber
M850-00T856/857 PCB InformationC6.1.5Copyright TEL 29/02/00Variant ComponentsA variant component is one that has the same circuit reference but different value or specification indifferent product types. Where two products share the same PCB, the term “variant” is also used todescribe components unplaced in one product. Variant components have a character prefix, such as“&”, “=” or “#”, before the circuit reference (e.g. &R100).The table below explains the variant prefixes used in T800 Series II products:Grid Reference IndexThis section contains a component grid reference index to help you find components and labelledpads on the PCB layouts and circuit diagrams. This index lists the components and pads in alpha-numeric order, along with the appropriate alphanumeric grid references, as shown below:If the variant prefix is. . . the component will. . .& change according to channel spacing= change according to frequency stability# change according to frequency range% change or be placed/unplaced for special applications*be unplaced in one product(where two products share the same PCB)circuit diagramreferencePCB layoutreferencecomponents listedin alphanumeric orderlayer number -1 = top side layer2 = bottom side layercomponent locationon the layersheet numbercomponent locationon the sheet
C6.1.6T856/857 PCB InformationM850-0031/09/98 Copyright TELUsing CAD Circuit DiagramsReading a CAD circuit diagram is similar to reading a road map, in that both have an alphanumericborder. The circuit diagrams in this manual use letters to represent the horizontal axis, and num-bers for the vertical axis. These circuit diagram “grid references” are useful in following a circuitthat is spread over two or more sheets.When a line representing part of the circuitry is discontinued, a reference will be given at the end ofthe line to indicate where the rest of the circuitry is located, as shown below. The first digit refers tothe sheet number and the last two characters refer to the location on that sheet of the continuation ofthe circuit (e.g. 1R3).C3014N7R30312DSGL31033UIF-SIG4R4C369100PC37110UR339100K%R338100DISCRIMINATOR1R32R92R98A2these grid referencesshow where the circuitis continued

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