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

[Tony Hwang]

Mark J Bailey (mjbtnus) wrote:
> 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.
>>
>>    
>>
>> ----
>> Your Moderator: Dick Flanagan K7VC: icom-owner at mailman.qth.net Icom
>> Users Net: Sundays, 1700Z, 14.316 MHz Icom FAQ:
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>>
>> -----
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>> 12/31/14
>>
>>
> 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
>
> ----
> Your Moderator: Dick Flanagan K7VC: icom-owner at mailman.qth.net Icom Users
> Net: Sundays, 1700Z, 14.316 MHz Icom FAQ: http://www.qsl.net/icom/ To
> support QSL/QTH.net: http://www.qsl.net/donate.html
>
> ----
> Your Moderator: Dick Flanagan K7VC: icom-owner at mailman.qth.net
> Icom Users Net: Sundays, 1700Z, 14.316 MHz
> Icom FAQ: http://www.qsl.net/icom/
> To support QSL/QTH.net: http://www.qsl.net/donate.html
>
>
> -----
> No virus found in this message.
> Checked by AVG - www.avg.com
> Version: 2015.0.5577 / Virus Database: 4257/8843 - Release Date: 12/31/14
>
>
Hi,
If that one fails, there will be no TX output. I happen to have a copy 
of service service manual. Also PIN diodes
Tony, VE6CGX