[R-390] AGC Troubleshooting

[Cecil acuff]

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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