[Heath] Yet more on my IP-27...

[Jerry Haigwood]

Ken,
    There has been considerable discussion of old electrolytic caps and how
to determine if they need replacing on another couple of lists I am on.  One
of the best ways to determine a bad electrolytic cap is NOT by measuring the
value of capacitance but rather measuring the ESR.  The ESR should be only
be an ohm or two at most.  Many times an older electrolytic will measure
correct capacitance but have an ESR of 10-20 ohms which is bad.  The higher
ESR will cause heating and in some cases, an explosion as the electrolyte
heats up to the point of causing pressure buildup or physical leakage!  If
you don't have an ESR meter, you might consider building or buying one for
future repairs.  I know some people who measure the ESR on all the
electrolytic caps before they actually start the repair.
Jerry W5JH

-----Original Message-----
From: heath-bounces at puck.nether.net [mailto:heath-bounces at puck.nether.net]
On Behalf Of Kenneth G. Gordon
Sent: Saturday, June 23, 2012 12:55 PM
To: Ron; Robert Groh
Cc: Heath at puck.nether.net
Subject: Re: [Heath] Yet more on my IP-27...

On 23 Jun 2012 at 8:56, Ron wrote:

>  > don't leave those old electrolytics in there!
> 
> I am not sure I agree. I've restored many, many Heathkit instruments 
> and in just about all, electrolytics that measured OK stayed that way 
> for a long time. Of course, all electrolytics will go bad *eventually*
> -- including brand new ones -- but this may happen 20 years later, or
> 50 years, or tomorrow...
> 
> -- Ron

Well, I suspect from what I have seen in this instrument while restoring it
that it had been abused over a long period of time by students at a
University teaching lab.

I am not too surprised at finding bad electroltyics in it.

However, although I don't routinely replace electrolytics in the equipment I
restore, I have found too many bad or leaky or leaking or weak ones to put
much faith in them...even when new.

When I finally replaced all the electrolytics in one of my SB-200s after one
failed (rather spectacularly too), all the remaining caps tested at less
than 1/2 of their original capacitance: many were down to 1/3 of their
original value.

Ken W7EKB
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