Re: Looking for a better in circuit ESR meter

Richard Knoppow

IN Circuit explains it. Of course, the problem is that you may have trouble discriminating what is in the capacitor from what is external to it. You are up against Kirchoff's law and its equivalents in AC (Norton and Thevinin).

On 5/16/2020 12:55 PM, Reginald Beardsley via wrote:
The issue is doing it reliably in-circuit on an instrument for which there is very meager service information. All I've got for the PS is a schematic with no part values. Multiple caps in parallel are shown as a single cap. And access makes removing the caps for better testing a major chore. It would be very difficult to get them back in and with almost 20 caps wedged together down under the edge of major chassis parts, it's not at all clear it could be done without completely disassembling the supply. The construction is such that it would probably take 4 hours to take apart and another 4 hours to assemble.

The PS has 9 output voltage adjustments and 8 connections on the PS connector. I've not yet determined where I can access the -12V output. The service manual procedure is "replace module". Test points? We don't need no stinking test points!

The PS connector was poorly chosen and the +/- 5 V connections burn up. This unit had a factory repair under warranty. It consisted of soldering the PS to the main board with #12 AWG wire.

The symptoms make me suspect that I've got noise on a power rail, but the SMPS makes it very hard to probe for that.

The LeCroy DDA-120 functions, but the front panel response is intermittent. I've replaced the cable and the switch contact board and I've swapped the processor boards without significant change in behavior.

I'm Not Having Fun!
Richard Knoppow

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