34A Power Trouble. I calmed down, here's the facts...

From: Tony Duell <ard_at_odin.phy.bris.ac.uk>
Date: Tue Nov 11 12:19:35 1997

On Tue, 11 Nov 1997, Tim Shoppa wrote:

> > > 1) A short somewhere on the secondary side (in one of the regulators,
> > > say). This will obviously cause too high a current to flow in the primary
> > > circuit
> >
> > How do I check that? I've never played with voltages over 24V before.
> A clamp-on AC ammeter is one choice - and its something that everyone
> with minicomputers should own or be able to borrow :-). You can buy them at
> Radio Shack, among other places.

That reminds me... I really must start seriously looking for a Tektronix
current probe for my 'scope.

A series light bulb is another trick. With all the loads removed from the
outputs of the regulators, the PSU shoulds run with (say) a 200W light
bulb (or enough smaller ones in parallel to equal this). The bulb should
be dim/out. If it's glowing brightly you can be sure that there's a short

This trick is more use on SMPS's where faults don't just trip the
breaker/fuse, they also blow expensive chopper transistors. I never power
up a repaired SMPS without some kind of limiting...


> It also won't hurt to do a continuity check on the breaker. If the
> connections aren't what you think they are, you've got a problem!

Unless it's one of those breakers with a separate connection for the trip
element (used in the RX01/RX02 I believe), I can't see how misconnecting
the breaker will cause it to trip only when the load is plugged in.

> Tim.

Received on Tue Nov 11 1997 - 12:19:35 GMT

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