14 May
2007
14 May
'07
4:44 p.m.
Message: 12
Date: Mon, 14 May 2007 09:32:35 -0500
From: Jules Richardson <julesrichardsonuk at yahoo.co.uk>
Subject: Old electrolytic capacitors (IME-86s calculator)
To: General Discussion: On-Topic and Off-Topic Posts
<cctalk at classiccmp.org>
Message-ID: <46487303.8040805 at yahoo.co.uk>
Content-Type: text/plain; charset=ISO-8859-15; format=flowed
...
They're in the power supply of an IME-86s
calculator and
are decidedly past their best :-) (At least four of the ten
in the PSU are showing signs of major leakage)
I'm the power supply guy in a large restoration effort.
http://www.ed-thelen.org/1401Project/1401RestorationPage.html
http://www.ed-thelen.org/1401Project/TricksForCapacitors.html
Fortunately, there were only linear supplies,
(suitable switching devices not yet available for switching
power supplies - another interesting game :-))
The machines (and currents) were large and most electrolytics
were the screw connector types.
After considerable experience, and using an ESR
(Effective Series Resistance) unit to verify
performance of the re-formed electrolytics, I went to
replacing only those capacitors with "major" leakage,
and testing ripple for "excessive" and that everything was
"cool enough" when power supply running rated voltage and current.
The rest of the machine *looks* healthy enough; once
I've replaced the electrolytics is there any good reason
not to slowly run the system up on a variac
(rather than giving it full AC from the start)?
A vital thing to watch out for in this business is motors.
Most types of motors depend on sufficient source voltage to get
started and generating "back EMF (voltage)" to limit current.
I was using the variac technique on an old key punch
when we began to hear a loud hummmm
- the capacitor start motor was not moving and getting warm :-(((
Interestingly, we have not had to "re-form" any capacitors
on capacitor start motors!! ?? I have no clue why.
One would reasonably expect some effort there.
Enjoy :-))