[R-390] Capacitors - Testing and identification.

[Drew P.]

Paul Galpin wrote:
 
"1. When I replace a capacitor, I test it by putting it across my 500V Insulation tester. Only if it comes down to infinity do I then
put it into the receiver. What is the general opinion of this? Is it adequate (for safety, of course, not capacitance value)"

This would be a good method if your insulation tester covers a sufficiently high range of resistance (they normally do), and if you do not expose the capacitor to voltage beyond its rating.  This assumes a DC test; for a capacitor will "conduct" AC! 

Electrolytics would be expected to show a much higher leakage than other types.

I like the method advanced in this forum a while back by Dr. Gerald Johnson; this used a DC power supply and a high impedance DC voltmeter (such as a VTVM or DMM) to indirectly measure leakage current at an appreciable voltage.

Paul went on:

"2. Everybody in the States seems to know what are Orange drops, BBODs, metallised foil, etc, etc. Over here in RSA, we don't seem to
have those ranges and certainly not down here in Port Elizabeth. 
But we do have second hand capacitors. Where could one get pics of these things to help ID the different sorts?"

I am surprised that Port Elizabeth, a large industrialized city, does not have electronic parts vendors who would stock the parts you would need.  Along with the previously posted Digi-Key you could also try Mouser (mouser.com).  Be advised that both of these organizations are in the US; international shipping will not be cheap.

Information on capacitor type identification and application can be found at the following page and by following links referenced therein:

http://en.wikipedia.org/wiki/Capacitor

More than you would ever want to know about capacitors as used in R-390A can be found under the heading "Capacitors" at:

http://r-390a.net/Pearls/index.htm

There you will also find detailed Dr. Gerald's method.

This is part of We-i Li's meisterstück "Pearls of Wisdom" which he has painstakingly distilled from this forum over the years. Kudos to Mr. Li!  

Drew