[R-390] AGC Problem - Diagnosis Help Appreciated

[Craig Heaton]

Tongue in Cheek:

It rains a few days here in Orygun and an old man needs something to do
besides counting raindrops. With that said, there are two main options.
Disconnect the old C551, leave it in place and mount the new one under the
chassis.

Or..........for devilment; The old oil filled cap has other uses. Take a
Dremil tool with a thin cutoff wheel and go around the inner edge of the
bottom side of the cap (next to the solder joint). The oil had other
medicinal uses and can be used to grow greener grass in the neighbor's lawn
that owns a plasma TV. Moving on.....with the inners exposed, take a wood
screw and twist it into the foil & paper wrapping. Grab the screw with a
pair of pliers and yank! Remove the cardboard insulation along the inside
walls and clean the case with your favorite solvent. 

Install new cap with heat shrink on the leads. Tack the bottom back on at
the corners with solder. 

Beats counting rain drops.

Craig,  

-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of David Wise
Sent: Wednesday, February 19, 2014 9:38 AM
To: r-390 at mailman.qth.net
Subject: Re: [R-390] AGC Problem - Diagnosis Help Appreciated

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,

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