[R-390] R390A antenna relay troubleshooting

[peter murphy]

 Thanks everyone for all the help. The first thing I did was disconnect the mini BNC's and connect the antenna there---effectively bypassing the relay. Result: no signal. So the relay is NOT the problem.  
I went in and removed and disassembled the relay anyway just to see how it worked. Turns out the middle contact was stuck closed. I manually worked the armature back and forth and now the relay works the way it should; when energized all the contacts open. In MGC and AGC they are all closed. I can tell this relay (a Dowkey) is looking pretty old and crusty, the armature does not snap open and  "clack" like in my other R390A.
So I guess I'm back to square one.  I've got a Y2K manual that I printed out years ago. My next step I guess is to check all the tubes in the RF chain to see if one is dead. I figure it must be either a dead tube, a bad cap or some sort of short somewhere because it failed so suddenly. 
Any suggestions are welcome. No formal electronics education here so be patient. I do have some test equipment though.  Scope, signal generator, VTVM, etc.  Are there test points in this radio that are easily accessed?  I don't have any tube extenders.
Thanks, Pete



    On Friday, March 16, 2018, 9:56:33 AM PDT, Bob kb8tq <kb8tq at n1k.org> wrote:  
 
 Hi

As long as we *are* on the topic of the selenium rectifiers …. they are a real 
stinker when they burn out. I’d vote for the “silicon replacement” approach. 

Bob

> On Mar 16, 2018, at 12:35 PM, David Wise <David_Wise at Phoenix.com> wrote:
> 
> Never mind, I didn't understand that your problem is "stuck picked", not "won't pick".  My post below applies to the latter, which is also a frequent problem.
> 
> Dave Wise
> ________________________________________
> From: r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> on behalf of David Wise <David_Wise at Phoenix.com>
> Sent: Friday, March 16, 2018 9:28 AM
> To: Bob kb8tq; Larry H
> Cc: peter murphy; r-390 at mailman.qth.net
> Subject: Re: [R-390] R390A antenna relay troubleshooting
> 
> Check the selenium bridge rectifier that powers the relay coil.  This class of component is characterized by gradual failure.  The voltage drop increases.  Mine was weak twenty years ago when I bought the radio.  In my opinion, there are two reasonable actions.  You can replace selenium with silicon, or you can add a reservoir cap to raise the average voltage.  I never liked the idea of powering a DC relay with unfiltered rectified AC, especially in a spot where hum can be a problem, so I put in a cap.
> 
> Dave Wise
> SWL in Hillsboro, Oregon
> ________________________________________
> From: r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> on behalf of Bob kb8tq <kb8tq at n1k.org>
> Sent: Friday, March 16, 2018 6:25 AM
> To: Larry H
> Cc: peter murphy; r-390 at mailman.qth.net
> Subject: Re: [R-390] R390A antenna relay troubleshooting
> 
> Hi
> 
> It’s also quite possible that Mr Spider has moved into the vicinity of
> the relay and clogged things up. A good visual is the first step ….
> 
> Bob
> 
>> On Mar 16, 2018, at 7:00 AM, Larry H <dinlarh at att.net> wrote:
>> 
>> Peter,  I've attached some pictures I have of the relay.  The 3rd one shows the 4 screws holding relay in place.  The 1st shows the armature that moves the contacts inside, 2 on 1 side and 1 on the other.  The 2nd shows the contacts that are operated with the cover plate off.
>> There might be something preventing the free movement of the armature.  It's possible that the electromagnet core has become magnetized.  If so, it can be demagnetized by applying low voltage ac to it or reverse the dc to it for a short time.  If it only takes a slight pressure to release the armature, then perhaps the spring leave tension from the contact springs is not strong enough.
>> Regards, Larry
>> 
>> 
>> <IMG_6769s.jpg><IMG_6770s.jpg><IMG_6775s.jpg>______________________________________________________________
> 
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