Using a Variac to revive power supplies - test-drb@ccmp.vtda.org

24 Dec 2010

Subject:
Re: Using a Variac to revive power supplies
From:
Tobias Russell <toby at pdp11.co.uk>
Date:
Thu, 23 Dec 2010 19:06:04 +0000

To:
"General Discussion: On-Topic and Off-Topic Posts" <cctalk at
classiccmp.org>

Ok, I suspected as much.

So for a linear supply such as the 8/E's is a Variac a valid way to go or
should I reform the capacitors individually as I've done previously?

All the best,
Toby

------------------------------------------------------------------------
Toby, I've found that removing every single electrolytic and reforming 
to full
(or 10% over) capacity provides the best results.   The Variac method -- 
while
better than nothing -- doesn't limit your current... plus doesn't reform 
all caps
to full capacity, nor tell you anything about their condition and leakage.

1.  Remove cap.
2. Check ESR.  If ok then..
3. Reform with resistor and variable power supply while monitoring 
current...
     raise input voltage slowly to keep max current to no more than 1ma.
     Let current settle down every so often to check for leakage rates
     at various voltages... One method I use is halves... start out at 50%
     rated voltage, let settle, then 75%, settle, then 87%, 95, 100....
     Checking leakage at each stage like this gives you an idea of
     cap condition.. so you can decide whether to replace or not.
4.  Check ESR again.
5.  Check capacity.
6.  If capacity is within 10% of spec, ESR is what it should be, and your
     leakage rates are acceptable, then you're good to reinstall.  
Otherwise,
     replace!

- John Singleton