Introduction. TB8100 Tech Notes/Tech Notes/TN 1189 VCO Out Of Lock Alarms TN
TECHNOTE/TN-1189_TB8100_VCO_Out_of_Lock_Alarms TN-1189_TB8100_VCO_Out_of_Lock_Alarms
TECHNOTE/TB8000/TN-1189_TB8100_VCO_Out_of_Lock_Alarms TN-1189_TB8100_VCO_Out_of_Lock_Alarms
User Manual: Pdf TB8100 Tech Notes/Tech Notes/TN-1189 TB8100 VCO Out of Lock Alarms
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Tait Confidential Tait Electronics Ltd TECHNICAL NOTE TN-1189 TB8100 VCO Out of Lock Alarms 21 June 2006 Applicability 1. TB8100 400 to 520MHz (H1, H2 and H3 band) Reciters using RF PCB 220-02025-08. Introduction Investigation was carried out on 3 reciters that were exhibiting TX and RX VCO out of lock alarms on the when they have been running for approximately 2 hours. The Service Kit reported several out of lock alarms on all three units under the following conditions • Hot and cold temperature extremes • Room temperature • Touching sensitive areas in both VCO’s and synthesiser cans 2. The Problem In all cases the synthesiser was actually locked and on frequency. The problem was the input voltage to the comparator that indicates an out of lock state was very close to the trigger point, just 21mV away on one of the reciters. Any noise on the DC supply or change in DC conditions with temperature will cause the comparator output to change, raising a VCO out of lock alarm. Alarms may be raised frequently enough to cause a buffer overflow, incrementing the watchdog reset counter and causing the Service Kit to appear to lock up. 3. The Solution A resistor change decreases the input voltage to the comparator to at least 300mV below the trigger point for an alarm. This was tested under the same conditions and eliminated the VCO out of lock alarms on all 3 reciters. A change has been raised to modify all production from the factory from 21 June 2006. RF PCB's that have not been assembled into reciters will also be modified. Both the TX and RX VCO's need to be modified. Telephone:+64-3-357-9991 support@taitworld.com http://support.taitworld.com TN-1189 Date of Print: 22/06/06 Page 1 of 4 Tait Confidential Tait Electronics Ltd Reciters in the field can be modified as follows: Change R1021 and R1124 from 100 Ohms to 47 Ohms. Tait part 038-12470-00, RES 0603 47R 5% 1/10W. On the RF board, remove the screening cans shown below. Remove this can for the RX VCO. Remove this can for the TX VCO. Locate R1021in the RX VCO and change to 47 Ohms. R1021 Telephone:+64-3-357-9991 support@taitworld.com http://support.taitworld.com TN-1189 Date of Print: 22/06/06 Page 2 of 4 Tait Confidential Tait Electronics Ltd Locate R1124 in the TX VCO and change to 47 Ohms. R1124 RX VCO schematic showing the location of R1021. TX VCO schematic is the same, component designations differ. R1021 changed from 100 Ohms to 47 Ohms Telephone:+64-3-357-9991 support@taitworld.com http://support.taitworld.com TN-1189 Date of Print: 22/06/06 Page 3 of 4 Tait Confidential CSO and Service Centre Instruction 4. Tait Electronics Ltd This change should not be needed on all reciters, only those with a fault report of VCO out of lock alarms. The factory reports approximately 20 of these have been picked up during testing in the past year. There is no need to recall any base stations in the field, this is an advisory note only. Issuing Authority Name and Position of Issuing Officer Jeff Northcott Senior Technical Support Engineer Confidentiality Confidential – This message or document contains proprietary information intended only for the person(s) or organisation(s) to whom it is addressed. All Recipients are legally obliged to not disclose Tait technological or business information to any persons or organisations without the written permission of Tait. Distribution Level Tait Only Document History Original Release Telephone:+64-3-357-9991 support@taitworld.com http://support.taitworld.com 21 June 2006 JN TN-1189 Date of Print: 22/06/06 Page 4 of 4
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