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

[Mark J Bailey (mjbtnus)]

I will check that. Would that component impact the no RF on Rx via the
SO-239 and/or tuner module?

-----Original Message-----
From: Icom [mailto:icom-bounces at mailman.qth.net] On Behalf Of Tony Hwang
Sent: Wednesday, December 31, 2014 6:04 PM
To: ICOM Reflector
Subject: Re: [ICOM] IC-765 tuner and total loss of RF from tuner circuit

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

----
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