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

[Mark Huss]

Had a similar problem with an R-392, very similar to an R-390. Receiver 
works fine, then suddenly looses sensitivity. Later comes back up. 
Traced it to the Break-In relay contacts being dirty. It suprised me a 
bit as I would think that the contacts would either make or not make as 
long as the contacts did not move. Considered that the voltage on the 
relay coil might be 'iffy', but the relay held to 16VDC. Burnished the 
contacts and everything works now.

William G Feldmann wrote:

>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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>  
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