[R-390] Local & Line potentiometers

[Craig Heaton]

Drew,

I should also add: All the electrolytic caps in both the Amelco & Motorola
have been replaced with new caps (not NOS junk). In trouble shooting the
Amelco, the caps were double checked on a TO-6A cap analyzer at rated
voltage, no leakage.

Regards,
Craig
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-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of Drew P.
Sent: Wednesday, January 01, 2014 8:29 AM
To: r-390 at mailman.qth.net
Subject: Re: [R-390] Local & Line potentiometers

Craig wrote:

"A little time was spent on the beast this evening.
1: No ground problems at the end of the pots, even added a jumper once
again. No change
2: Checking the audio at the CCW ends, less than 5 millivolts with the
O'scope.

Going to check a few more items tomorrow; swap IF's between the Motorola and
Amelco again. This should rule out AGC issues there. Then on to the RF
section."

I'm not convinced that it could be an AGC problem.  In the couple of
R-390A's I've operated, the audio gain pots work normally even in MGC mode
(which disables AGC), and with RF gain all the way up and the receiver
overloading on a strong signal.

My vote goes for one section of the three section plug-in electrolytic cap
being open with resultant loss of decoupling.

Drew
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