Testing caps on Zenith 20Y1C48

[Carmine]

Well I tried to test the caps on my Zenith, only to get results that don't seem to jive with anthing I've been told!

I'm using a Sperry digital meter. On the lowest setting, (2000 Ohms I believe) I get basically nothing. Moving up the scale to about 20K Ohms, I'll get something like .18, this will SLOWLY tick down to about .16, and then stay fairly steady. In other words, the readings don't seem to indicate anything! All of the caps do the same thing (sometimes with different numbers), even the new cap I installed. I am testing with the caps in-circuit, observing polarity.

I know I could just replace all of the suspected caps as earlier suggested, but I don't like such shotgun approaches (Especially at about $6 per cap) I would really like to find what's wrong! As I mentioned in an earlier post, voltage readings to the 6HE5 Vertical output tube were incorrect. I had 18 volts at pin #4 (should be 26) and 316 volts at pin #10 (should be 280).

What am I doing wrong?

[andy]

The best thing I've used to check caps is an ESR meter. Electrlytic caps usually either short, or develop high internal resistance. Shorts are easy to find, but a cap with high ESR may test close to its rated capacitance. The analog ohm meter test is often inconclusive and a DMM's ohm range is totally useless for this as you've seen. There's an excellent kit available here which allows in circuit ESR testing. The first thing I do now is check all the electrolytics and replace any that are higher than normal. Now I don't have to replace a lot of good caps to make sure no marginal ones are left in. If you ever work on switching power supplies, it will pay for itself one the first repair. For small caps, a decent digital cap meter is good.

http://www.anatekcorp.com/testequipment/esr.htm