19 Dec
2015
19 Dec
'15
11:04 p.m.
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Mouse
Sent: 20 December 2015 01:46
To: cctalk at classiccmp.org
Subject: Re: VAX 4000-500 PSU Overload?
I think the suggestion was to put an
ammeter between the PSU and the
backplane.
Yes...but ammeters (for nontrivial currents) are generally just voltmeters
across current-sense resistors, and it's the current-sense resistor that
needs
But getting something in series to measure load is
going to be
really awkward, [...]
As in, you don't have any such thing to put in series,
or you don't
see a good way to get it in series? [...] to carry the current and thus requires attention.
The problem is just how to physically do it. But in any case I don't think
it is necessary to do this now, as I have been able to reproduce the problem
on the bench now. It looks like the 12V side starts up and then shuts down,
sometimes after a few seconds, sometimes after a couple of minutes,
sometimes it does not even start to output the right voltage. I am pretty
sure that it is falsely detecting overcurrent. The problem is going to be
finding and fixing the part that is not working, there are a lot of tiny
surface mount components that seem to process the signal from the current
sense resistor....
Regards
Rob