[R-390] AGC Troubleshooting

[Barry]

Well, the R390 could certainly use an HVAC system...  :-)

Barry - N4BUQ

----- Original Message -----
> From: "David Wise" <d44617665 at hotmail.com>
> To: "Cecil acuff" <chacuff at gmail.com>
> Cc: "R-390 Mailing List" <r-390 at mailman.qth.net>
> Sent: Tuesday, March 12, 2024 1:09:34 PM
> Subject: Re: [R-390] AGC Troubleshooting

> Oops AGC. It said that at first, and then auto corrupt changed it to HVAC. Good
> times.
> 
> Dave Wise
> 
>> On Mar 12, 2024, at 9:56 AM, Cecil acuff <chacuff at gmail.com> wrote:
>> 
>> It’s been my standard practice to replace all paper caps in the “A” model radio.
>> You may be able to find the single culprit but next week, or month there will
>> be another. I would just bite the. Bullet and replace them all!
>> 
>> Cecil
>> 
>> Sent from my iPhone
>> 
>>> On Mar 11, 2024, at 5:44 PM, gary.biasini at shaw.ca wrote:
>>> 
>>> I followed Charles Steinmetz's troubleshooting procedure for AGC issues and
>>> the following resulted after tuning to a very strong BCB station:
>>> 
>>> 
>>> 
>>> Voltage Terminal 3  & 4: -0.37V - not good
>>> 
>>> 
>>> 
>>> Then step 2:
>>> 
>>> 
>>> 
>>> Resistance Terminal 3: 460k - maybe passable
>>> 
>>> Resistance Terminal 4: 24.6k - horribly off spec
>>> 
>>> 
>>> 
>>> So, my problem is most likely in "any of the several dozen bypass caps on
>>> the AGC line in the IF and RF sections, or leakage to ground in one or more
>>> of the mechanical filters".
>>> 
>>> 
>>> 
>>> Now my ignorance shows up.  How do I identify what are bypass capacitors?  I
>>> assume that these are capacitors that go to ground?
>>> 
>>> 
>>> 
>>> I also note that, on the very strong BCB station, I get no sound output
>>> until the RF gain is up to 8, if that helps narrow down where I should start
>>> searching.
>>> 
>>> 
>>> 
>>> Thanks in advance for any help.
>>> 
>>> 
>>> 
>>> Regards,
>>> 
>>> 
>>> 
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