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

Sun Nov 30 10:41:55 EST 2014

Hi

This is why I cringe a bit when people decide to wholesale re-cap some of these radios. The parts in there have made it past infant mortality and various instal / damage issues. You are trading one set of things for another. 

Now, indeed there are some sets that simply will drive you nuts until you find every last horrible cap in them. By now those are pretty well identified in each of the various radios. Those, yes you replace. It’s shotguning everything in sight that worries me.

Bob 

> On Nov 30, 2014, at 12:50 AM, Dennis Wade <sacramento.cyclist at gmail.com> wrote:
> 
> 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
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