[R-390] AGC Troubleshooting

David Wise d44617665 at hotmail.com
Tue Mar 12 14:12:45 EDT 2024


For sufficiently small values of HVAC, several R390s have had HVAC installed!

Dave Wise

> On Mar 12, 2024, at 11:11 AM, Barry <n4buq at knology.net> wrote:
> 
> 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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