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

Sun Nov 30 10:45:24 EST 2014

I guess it all depends on your perspective Bill and your skill level.  I've done several and I would never say any of them have been in poorer condition than when I started....if your skill level is such that your finished work is poorer than when you started then you should take up a different hobby.

Few of these radios are museum pieces, the best we can do with them is make them sing by doing electrical restoration work that will put them in the best possible working condition we can and then enjoying them.

And yes while I had it apart I would definitely check all the tubes and many of the resistors....all of which can be checked easily without removal in most cases. (resistors) The problem with checking caps in many cases is you have to lift one end and by the time you do that it's just about as easy to go ahead and lift both ends and replace the thing. (I test at rated voltage with an LC-77)

I would also be curious what brand, type and rating the failed cap was....

Sounds crazy to have a replacement fail in 10 years.

One final comment...I'm not a shotgun tech...never have been...but when a component type shows a pattern failure and is known to be a problem I do use a blanket approach to its replacement....that's not shotgun sir..

Case in point...I would never suggest one blanket replace the type paper caps in the R-390/urr....historical data does not indicate it because quality parts were used to start with.

It's your radio, do with it as you please but in the case of the paper caps...if it's an R-390A..I do know....they will fail and sooner than later...

Cecil
K5DL

Sent from my iPad

> On Nov 29, 2014, at 11:34 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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