[R-390] R-390 Digest, Vol 174, Issue 11

[dog]

Well, today it wouldn't do it. That's after I left it off all night. 
What I do notice though (noticed this for a long time) is turning the 
bandswitch produces a lot of noise (static), especially just before it's 
going to lock into a band. It's fairly consistent as to which bands I go 
into, especially 14 and 27.  I think I'm going to have to pull that RF 
section again and clean the bandswitches. But I get the feeling that's 
it's something else, related. Sometimes when I go to a band, it doesn't 
produce full output, like in the past when it's on low gain, but 
changing to another band and back makes it full volume again. I can't 
always do it just rocking on a particular band that is low. Sometimes 
I'll go to a couple bands with low gain in a row but once I hit one with 
regular gain, it all goes back. Fair amount of static involved too.

There may be several things going on. I still get the feeling that the 
'static or noise' shock may do something to a component that makes it 
erratic. Maybe doing the gain checks at the test points like suggested 
may tell me something. Actually most of the time the RX sounds fine, 
once I get to a place I want.

Lots of good suggestions.

Dave


On 10/14/2018 10:58, shelly199--- via R-390 wrote:
> Hi Dave,Sounds like you have to isolate the problem.  I think I would start by putting a 455 KHz signal with some modulation into the IF unit at about 75 uv, monitoring the diode load voltage and listening to the audio out at startup.  If you're good there then start putting a signal into the various test points in the rf deck.  Put signals in starting at E208 then E209, E210, E 211 and T208 output.   Do this in MGC only.
>
> I've had similar problems and have found that mica caps with B+ on them are the most failure prone components in the radio and the toughest to pinpoint.  That's what I would suspect and probably in the rf deck.  Good luck!
>
> In a message dated 10/14/2018 10:07:05 AM Eastern Standard Time, r-390-request at mailman.qth.net writes:
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>    1. Re: Gain drift (dog)  2. Re: Gain drift (Larry H)  3. Re: Gain drift (dog)  4. Re: Gain drift (Larry H)  5. Re: Gain drift (dog)
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