[R-390] R-390 (Non A) Problems

[William G Feldmann]

Hi David,

I would also check on some other bands using different front end coils like
below 8mc and above 16mc just to eliminate any possible problem in the front
end coils or transformers.  If a front end transformer is bad it's most
likely a bad SM cap but I've only worked on the A model's transformers that
are a snap to remove and fix.  Hopefully the non-A ones can be removed by
just pulling the slug racks and removing a small screw in the center of the
coil like on the A.  But don't know, never had any problems with them in my
non-A.

Also check the AGC is working by looking at the AGC line voltage and being
sure the receiver seems to not be overloading on strong signals.  If the AGC
is working OK and the RF stages are OK, then you most likely have a problem
in the carrier meter circuit.

Try and see if there is a difference between meter reading on the same
signal when switching between MED and SLOW AGC.  If there is a meter level
difference the 2uf oil filled cap on the plate of the meter amp in SLOW is
most likely leaking.  It's C551 in a A model but will be a different
reference number on the non-A model.

If the AGC is working it's most likely a cap or resistor that's failed in
that meter amp circuit.

Also be sure the carrier meter just isn't pinned below zero.  That meter
zeroing pot trouble some and is very hard to adjust.  I usually replace it
with a ten turn one.  I'll mention that in my part 2 article in the Sep.
issue of ER.  Hopefully nothing has damaged the meter because stock ones are
very hard to fine thanks to the demil process most have gone through.

Anyway the problem is most likely in the IF module that's easy to pull and
run out of the radio.  On my A model I could lay it on its side on a piece
of wood on top of the radio and still connect the cables for testing as I
mentioned in my article in the Aug issue of ER.  I think you should be able
to do that on a non-A.  I have a Collins non-A R-390 that hasn't had any
problems besides a few weak tubes.  But I sure went through hell with bad SM
caps in the front end of my Stewart Warner R-390A that I talked about in my
part 1 ER article.

I'm at my second house in Mammoth Lakes but when I get back to Palmdale I'll
look some more at the manual for my non-A for some ideas if your still
having trouble.  Let us know how you are doing.

Good hunting David,

Bill N6PY


----- Original Message -----
From: "David C. Hallam" <dhallam at rapidsys.com>
To: "R-390 at mailman. qth. net" <R-390 at mailman.qth.net>
Sent: Wednesday, August 16, 2006 10:08 AM
Subject: [R-390] R-390 (Non A) Problems


> My R-390 has developed a problem.  I wonder if anyone has experienced a
> similar condition and what they did to correct it.
>
> The receiver suddenly seemingly lost sensitivity and the carrier level
meter
> was not responding.  I checked the tubes in the carrier level circuit,
both
> with my tube tester and by substitution, and found no bad tubes.
>
> Testing the stage gain as outlined in paragraph 53 of the manual, I used
my
> signal generator to supply a 14.2 MHz signal to test point E206 (grid of
> V201 1st RF amplifier.)  A signal of 12 uV gave me a reading of -7 V on
the
> diode load terminal.  Spec for this test is 4-16 uV to obtain -7 V.  I
still
> have to do an additional test with input at the antenna input where the
spec
> is 1-4 uV in case the problem is in the input transformers.  However, as I
> read the result of the first test, the receiver is probably working OK.
> There is still no movement of the carrier level meter, or at least only a
> very slight movement off of zero.
>
> David
> KC2JD
>
>
>
>
>
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