[R-390] RF Deck B+ short (390A)

[Bill Hawkins]

Well, if you feel that way about it, might's well replace all the tubes
and all the resistors, because you never know.

If you do that, there won't be an original solder joint left, leaving
the set in poorer condition than it was.

Bite the bullet and prepare to find the next problem, if it happens in
your lifetime.

Shotgunning is like saying, "Kill them all and let their god sort them
out."

No flame intended - never liked the shotgun approach. Besides, you won't
have to buy mystery novels when you've got the occasional real mystery
to solve. It's good mental exercise, right Roger?

Kind regards,
Bill Hawkins

 

-----Original Message-----
From: R-390 [mailto:r-390-bounces at mailman.qth.net] On Behalf Of Cecil
Sent: Saturday, November 29, 2014 8:45 PM
To: Larry H
Cc: R-390 HF Receiver List
Subject: Re: [R-390] RF Deck B+ short (390A)

Sounds like a great candidate for a complete recap...you never know when
the next one will let loose...

Cecil
K5DL

Sent from my iPad

> On Nov 29, 2014, at 8:04 PM, Larry H <dinlarh at att.net> wrote:
> 
> Hope everyone had a nice Thanksgiving.
> 
> Dennis,  Looks like good progress.  Yes, C248 is a good possibility.
If not, your problem is probably in the plate coils for V201 - if any 1
of the coupling caps C249 through C254 short, all bands will be shorted
to ground through the coils Z201-1 through Z206-1.  An easy way to track
down which one would be to use an ohm meter that measures very low
resistance fairly accurately and measure each one.  If that is not
feasible, measure across C248 and pull each tuning assemblies just
mentioned one by one.  You'll find it.
> 
> Regards, Larry
> 
> 
> ________________________________
> From: Dennis Wade <sacramento.cyclist at gmail.com>
> To: R-390 HF Receiver List <r-390 at mailman.qth.net>
> Sent: Saturday, November 29, 2014 5:13 PM
> Subject: Re: [R-390] RF Deck B+ short (390A)
> 
> 
> Good evening all.  I hope everyone had a wonderful holiday.
> 
> Well it took a little longer to get back to this than I thought, but I

> did pull the tubes and looked at the resistances from plates to 
> ground.  V201 shows a dead short, and the plates of V202, 203 and 204 
> show about 2.4K ohms to ground instead of the 20K nominal the manual 
> specifies.  I get infinite resistance from V205A and B, 206 and 207, 
> but the deck is out of the mainframe.
> 
> Looking at the schematic, my untrained eye sees that C248 (5000 pf to
> ground) is a likely suspect, with C254 and C276 being less likely.  
> The 2.4K I'm seeing on the other plates is likely R205.
> 
> Thoughts?  Think I'm getting warm?  :)
> 
>           Dennis
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