[GLLUG] multimeter

Jason Watson watson.jason at gmail.com
Fri Mar 17 17:27:42 EST 2006


On 3/16/06, STeve Andre' <andres at msu.edu> wrote:
> On Thursday 16 March 2006 16:20, Caleb Cushing wrote:
> > can someone bring a multimeter to the group tonight so I can make sure my
> > power supply is stable.
>
> I can't get there, but something to remember is that a multimeter may
> well say your ps is at 3.3 and 5.0v (etc), but not show you ripple, or
> variances in voltage over time.  Test it, but be aware this is will find
> gross errors only, not the more tricky ones.  A digital storage scope
> would be needed for those.  Is it likely to need more advanced stuff?
> No, but the perverse errors aren't caught with the simpler tools. ;-)
>
> --STeve Andre'

Along with any multimeters and other test equipment there are also
some gotcha's with testing ATX power supplies.  Usually you'll have to
short the PS-ON pin (Pin 14, wire is usuallly green) to one of the GND
pins (pins 13, 15, 16 or 17, wires are usually black) to get some of
the other voltages to turn on.  Also note that some supplies will not
regulate correctly with some kind of load or minimum current draw. 
This is where one of the little ATX power supply testers comes in
handy.  Also the handy testers will not usually check for the more
'perverse' errors like ripple and you'll still need an o'scope to
check them.  Unless you already own most of the test equipment it's
usually more economical to just swap with a known good power supply
and see if it makes a difference.

--Jason Watson



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