[ICOM] IC-765 tuner and total loss of RF from tuner circuit

[Tony Hwang]

Mark J Bailey (mjbtnus) wrote:
> My 765 lost all RF output from the RF Out jack some time back. Since I
> wasn't transmitting all that much at the time, I only mucked around with the
> tuner module a little bit back then to troubleshoot. The receiver seems in
> good shape as when I pull the RCA cable off Rx In and Rx Out and attach a
> random wire to the Rx In, I get good RF for Rx on all bands. Suspecting a
> relay in the tuner module, at the time I swapped out RL201 on the
> antenna/accessory board. No go. RL13 appeared OK, so I didn't do anything
> with it.
>
>   
>
> I eventually gave up with other things pressing me for time. Recently, I
> started look at this issue again. This time I swapped out RL13. But no go
> still. It is almost as if the tuner is stuck on the transmitter circuit. The
> tuner tracks with the VFO, but hitting the tuner buttom does not alter RF
> for Rx through tuner. Since the Rx is A-OK on the Rx In port, I still
> believe the issue is in the tuner module. But, not being a hardcore
> electronics guy with all the bench gear to really dig into the block
> diagrams of the tuner module and related testing and what not,
>
>   
>
> I was hoping someone here might chime in to guide me deeper into the
> mystery. I love my 765 and really would like to get it back on the air. I
> suppose I could send it off, but who these days still services these? Since
> I did reasonably well on swapping out RL201 and RL13, I think could tackle
> most anything that was not IC or surface mounted, so if I could pin this
> down, I'd much rather succeed in fixing it myself. One thought I also had
> was could the tuner controller board have fubared?
>
>   
>
> I know there are several other relays in the tuner module. What is the best
> practice for testing relays such as these while they are still inboard?
>
>   
>
> I should add that in receive on the Rx In port, i get strong RF and meter
> indication. In fact, it is totally nominal - sensitivity on all bands is
> great. you wouldn't know there was a problem. But when you patch Rx In back
> over to Rx Out and attach the coax to the SO-239, it is like there is no
> antenna attached at all. I've tried hitting the power on and off rapidly in
> succession, Transmit / Receive toggled in rapid succession, and Tuner In and
> Out in rapid succession - Rx is dead. Preamp and AGC still seem to work fine
> too on Rx, FWIW.
>
>   
>
> One other tidbit that might be pertinent.  with the antenna attached to the
> SO-239 and if I try to transmit, I get considerable frontend
> feedback/overload - not at all nominal! Needless to say, I only tried this a
> very limited number of times when the problem first appeared, and have been
> reluctant to do so any further for fear of burning something out in the Tx
> finals. So, in transmit, it does not appear to be able to get RF out through
> the tuner module to the antenna either. Perhaps knowing this might help
> narrow this down some?
>
>   
>
> I have posted this also on the IC-765 Yahoo Group, but had the brain fart to
> also seek you guys out too! Sorry it was a bit winded. :)
>
>   
>
> Thanks for listening! 73s, Mark, W4MJB.
>
>   
>
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Hi,
The driver transistor for PA is known to go. I had to replace it with 
heavier spec. one once.
You can check the x-sistor with just multimeter.
GL, Happy new year.
Tony, VE6CGX