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 ... 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. 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 :-))