[R-390] Servicing Advice on Signal Generator URM-25D

[N4BUQ at aol.com]

I know the brown beauties in my Motorola decks were visibly cracked and, 
therefore, had probably taken in moisture and as a result were most likely bad.  I 
replaced them wholesale with OD's.  Not sure if I'll do the same on the 
current unit as the ones in it appear physically in better shape, but I think I'll 
probably replace them.  I've just heard too much about the life expectancy of 
them to take chances.

Barry(III) - N4BUQ


> There are brown colored capacitors that resemble the design of the black 
> beauty cap.  I think it has been accepted by most that those caps are as 
> prone to failure as the black beauty and they are being replaced for that 
> reason.
> 
> Personally I haven't had a chance to check any of them to see if they have 
> the same leakage characteristics as the infamous black beauty or not.  I 
> can't say I have noticed any that are cracked, but I do believe I have heard 
> 
> stories about some that were found to be.
> 
> I'm not sure what the Pro's who are restoring these radio's for profit (I 
> use that word loosely...I've been there) are doing...I expect a wholesale 
> replacement of paper caps as evidenced by the cap kits that are offered by 
> some.  Problem is if you leave them in you will always be nagged by that 
> question floating around in your mind about whether the performance could be 
> 
> improved by replacing them.  You could lift one end and check them as long 
> as you do it correctly by measuring them at their rated voltage...but by 
> that time you are half way to replacing the darned thing so why not go ahead 
> 
> and finish the job...right!  I don't know...what's the right answer...is 
> there really any harm in replacing them if you are up to doing the job and 
> it's done properly.  Is there any documented evidence that replacement 
> degrades performance...I would guess not.
> 
> Resistors...now they are a little easier.   Not hard to measure usually. 
> Some spot checks will usually give you a pretty good idea if work is needed 
> or not.
> 
> I certainly don't advise unnecessary replacement of parts....but for the 
> most part paper caps have a very bad reputation.  I don't trust them!
> 
> Cecil Acuff