cobra 2000 gtl counter issue

[DT307]

brief history i am a kitchen tech from the uk but dont see many of these and no point banging my head against the wall if a common issue .....everything was going fine and i sold this radio for a friend and about a month later was told of a problem with the counter on ssb reads 33.3333 rx and tx and on am rx its 25.5333 and am tx its back to 33.3333. (7.8mhz difference )
whats been done ......counter recap and the service mod to ic512 no change
traced the 7.8mhz through the fet tr516/517 and it is getting amplified and looks clean.
following on from there through ic507 and a pulsed output is present on pin 8 of ic505.
traced the 34mhz again fet/ic512 to pin 8 if ic505 with about the same pulsed amplitude as the 7.8mhz sig.
also on the same pin i have the sum and minus of both frequencies at a much much lower p2p level.
now moving on on pin 12 of ic505 i have a good 34mhz pulsed signal but the 7.8mhz is there but is quite low and in turn low on the input pin9 of the decade counter ic506 .
thats as far as i went fault finding before i wanted to smash it lol
ps the 9v and 5v rails working.
thanks for looking and i hope some 1 seen this problem 1000's of times and say its part ****

regards DT307

 

[DT307]

brief history i am a kitchen tech from the uk but dont see many of these and no point banging my head against the wall if a common issue .....everything was going fine and i sold this radio for a friend and about a month later was told of a problem with the counter on ssb reads 33.3333 rx and tx and on am rx its 25.5333 and am tx its back to 33.3333. (7.8mhz difference )
whats been done ......counter recap and the service mod to ic512 no change
traced the 7.8mhz through the fet tr516/517 and it is getting amplified and looks clean.
following on from there through ic507 and a pulsed output is present on pin 8 of ic505.
traced the 34mhz again fet/ic512 to pin 8 if ic505 with about the same pulsed amplitude as the 7.8mhz sig.
also on the same pin i have the sum and minus of both frequencies at a much much lower p2p level.
now moving on on pin 12 of ic505 i have a good 34mhz pulsed signal but the 7.8mhz is there but is quite low and in turn low on the input pin9 of the decade counter ic506 .
thats as far as i went fault finding before i wanted to smash it lol
ps the 9v and 5v rails working.
thanks for looking and i hope some 1 seen this problem 1000's of times and say its part ****

regards DT307

ALL SORTED was a bad ic

 

[nomadradio]

Cool!

Congratulations, that's not an easy item to troubleshoot.

Which chip was it that blocked the 7.8 MHz tracks?

73

 

[DT307]

hi bro i was looking at it wrong and looking for frequencies where i should have been looking at the amplitude of the pulses to cut a long story short i had a spare counter showing 92 mhz that i forgot i had here so sorted that (just alignment) and i was reading the exact same p2p voltages all the way through both the counters stages and the patterns were also good upto and including ic506 pin 9 tc5032p decade counter input.....knew then was a bad ic506 ......removed the bad ic and test fitted in my working counter (some 1 installed a socket ) and hey presto the counter stopped working and displayed 33.3333 .........ps are you the same nomadradio (Chris) that works on james radios ... i gave some help with a jackson rx/tx switching and a gerhard maurer module a long time ago? if so hi again bro.......if not just hi lol