Capacitors on M8722 Board

Tony Duell ard.p850ug1 at
Sat Sep 4 04:58:49 CDT 2021

On Sat, Sep 4, 2021 at 10:35 AM Rob Jarratt via cctalk
<cctalk at> wrote:

> I lifted it to measure its capacitance and ESR. It measures about 80uF and

With a lot of capacitance meters, a leaky capacitor will read high. So
that may explain why it's reading 80uF

> the ESR seems OK. I am unsure whether to replace it, and if so what voltage
> rating should I replace it with? I don't understand if this is a 30V rated
> capacitor or 20V. It seems that Unibus has some 20V signals, so I guess 20V
> might be right? I don't think 30V or 20V parts exist though, so I would need
> to get 35V or 25V. Maybe the voltage rating isn't too critical?

In general you can always replace a capacitor with one of a sensibly
higher voltage rating if there's space for it. It's the maximum
voltage that the capacitor will stand before it breaks down and passes
DC. In other words, a 35V or 63V one would be fine here.


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