[R-390] AGC Problem - Diagnosis Help Appreciated

[David Wise]

Just replace it.  It's bad.  It's always bad.  If I saw a good original C551, I'd faint.

To expand on what Craig said, if you simply measured resistance with an ohmmeter, the figure you got is wildly optimistic, because leakage increases faster than proportionally as applied voltage increases.  50Meg is incontrovertible evidence of failure.  Once it charges, a good cap will read open.

The only difference between SLOW and MEDIUM is the voltage applied to C551.  (Polarity too, but that shouldn't matter here.)  If it sort of works on MEDIUM but fails on SLOW, C551 is THE suspect.

Dave Wise
SWL in Hillsboro Oregon

-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net] On Behalf Of Craig Heaton
Sent: Tuesday, February 18, 2014 7:50 PM
To: 'AE4CW'; r-390 at mailman.qth.net
Subject: Re: [R-390] AGC Problem - Diagnosis Help Appreciated

Chuck,

With my limited listening to SSB with a R-390/A, MGC adjusted to somewhere
around 6 or 7 and Local gain around 4 or so seems best. AGC and SSB never
seems to cut the mustard, but I don't use it for SSB. YMMV

On Slow the carrier meter goes to 100+ and AGC is lost. C55I would be my
target, did you check insulation resistance at rated voltage? Need a cap
checker/analyzer. Both of my receivers had faulty C551's. Value checked good
on the cap analyzer, insulation resistance was terrible. I've used a NTE
MLR205K630 with good results. 

Craig,