Wednesday, January 18, 2012

More Capacitor Testing Adventures


Having an ESR tester around the shop is a useful thing when it's time to start looking at the electrolytic capacitors in an amp. I had been using my ESR Micro 3.1, made by Radio Devices in beautiful downtown metropolitan Tver, Russia about which more later.
All was going swimmingly until I went to test a capacitor that had an open ground and was thus chock full of juice-the ESR Micro 3.1 popped and although this is supposed to be an easy fix the diodes and 100 ohm resistor that are supposed to protect the innards seem OK so I figure one of the ICs is gone....where was I?

Oh. I remember. ESR, or equivalent series resistance, is a good metric for checking older electrolytics. The idea is that as a capacitor deteriorates over time it will build up internal resistance that can be used as an indicator of condition.

Well. What to do?

I didn't have three weeks to get another from Mike Klykov although I think I may anyway, so I ordered this ESR tester off of Amazon that came for about $50 shipped.

Of course it's made in China, and of course it has the obligatory "QC passed" sticker and of course it didn't work right. It wouldn't zero but occasionally could be persuaded to go full span if the panel was pressed on. I guess that's what passes for QC in China.

So there I was, faced with the prospect of boxing it up, shipping it back, and screwing around for another couple of weeks.

I figured it was worth a try to fix it, so I whipped the back off, removed the circuit board, resoldered the tabs on the zero set trim pot, shot the pot full of contact cleaner, and put it back together.

Now, I can put my own QC Passed sticker on it because it works just fine.

The MAT Electronics MUL3333 ESR tester is an analog meter contained in a substantial case, large enough to hold the 6 AA batteries you're going to need. It comes with test leads which I shall modify with alligator clips. One thing I like about the ESR Micro is that needles are soldered to the alligator clips, making it easy to poke through the lacquer and get into a trace.

The instructions are pretty straightforward even if the translation into English is a little strained at times. It tells us that the internal frequency of this device is 66khz, and from what I read this is an AC ohmmeter with an internal power source.

Electrolytic capacitors ESR tends to increase over time as the electrolyte dries out or the integrity of the seal is compromised. If the ESR value rises, it is the first sign of a capacitor that's on its way to glory. It's a worthwhile test for any shop bench, and if you're like me and can't afford a Sencore LC3, a simple tester like this is the way to go.

We're going to give this tester a run for its money and we'll have a fuller report. And we'll still order another ESR Micro 3.1.

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