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

[Dennis Wade]

Well, the winner is....

           C248  Dead short.  What threw me was it was a cap I replaces
about 10 yrs ago when I selectively recapped it.  Didn't expect a newer
part to go.

         So now to button it up and make sure it doesn't blow fuses
anymore.  As far as I can tell, there's no reason I can't power up the
receiver with the panel dropped?  I want to be able to apply power with as
little reassembly as I can get away with just in case.

          Thank you all for the advice.  It helped a lot.

                   Dennis

On Sat, Nov 29, 2014 at 9:34 PM, Bill Hawkins <bill at iaxs.net> wrote:

> 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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-- 
"If they trust you, it is an extraordinary privilege, and you simply can't
abuse it."
      - A. Alan Post  1914-2011.  California Legislative Analyst 1949-1977.

-------------------------
Dennis L. Wade
KG6ZI
Carmichael, CA