[AMRadio] Muting the R390 on transmit

John King k5pgw at yahoo.com
Wed Dec 2 11:46:05 EST 2009

Thanks for the source of information, Jerry. I have looked at the schematic on the Y2K site and see relay 601, the break in relay. Now I must physically locate it and determine if the relay is indeed bad. I have 12.95 vac at terminal 9 on the terminal board  on rear of R390. Now to locate the relay and determine if a component between the power source and the relay coil is bad. I suspect a resistor that may be in series with the relay coil voltage supply  "in my imagination" because I haven't located such a resistor. I remember a faint smell of hot carbon when I first attempted to energize the relay by grounding terminal 9 and additionally, I observed slight arcing when I connected the grounded alligator clip to terminal 9.  If the foregoing tells you anything, please feel free to direct me. Thanks again and 73, John, K5PGW

From: Jerry K <w5kp at hughes.net>
To: Discussion of AM Radio in the Amateur Service <amradio at mailman.qth.net>
Sent: Wed, December 2, 2009 7:33:20 AM
Subject: Re: [AMRadio] Muting the R390 on transmit

Greetings, John... 
I noted you said you didn't have a manual or schematic for this 
receiver. Before you do anything else, do yourself a giant favor and go 
to these two websites:

R-390A FAQ Page <http://www.r-390a.net/faq-refs.htm>
An exhaustive list of carefully gleaned technical references on this 
fine receiver, in downloadable PDF format.

R-390A Y2K Manual (Release 3) <http://www.r-390a.net/Y2K-R3/index.htm>
A complete annotated and updated version of the R-390A Technical Manual. 
This manual has been painstakingly compiled, rewritten for clarity and 
accuracy, and is kept updated by a large group of experienced techs who 
own and have worked on the R-390A for many years. Downloadable (PDF 
files) by chapter, or as one massive file.

Just about anything you need to know is available on these two web 
pages. I have only rebuilt five of these great receivers over the years, 
and I have a complete set of the original military versions of the 
R-390A manuals, but like most of us R-390A nuts the "Y2K" manual is my 
working bible for this receiver. It is much easier and faster to use 
than the original military versions. You will benefit (at no charge, no 
less!) from the hundreds of hours invested in updates, corrections, and 
clear, easy to follow troubleshooting information contained in the 
latest release of the Y2K Manual. These guys have invented the wheel for 
you, don't waste time reinventing it. :)

Have fun, Jerry W5KP

John King wrote:
> Thanks for the reply, Grant. My R 390 doesn't mute when terminal 9 is grounded. I have connected an alligator clip lead to terminal 9 and then connected the other end of the clip lead to terminal 16 which is ground and there is no effect. I can't figure out why there is no effect when terminal 9 is grounded. What do you think, Grant? I do not have a manual or schematic for the R390. 73, John, K5PGW
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