Re: [gentoo-user] {OT} Power supply or motherboard dead?

[Alan McKinnon]

On Thursday 20 March 2008, Marzan, Richard non Unisys wrote:
> Get a volt meter and measure the voltage. Red is 5+ volts yellow is
> 12+ volts; if you're getting less than that or way too much than
> those values then the component needs to be replaced.

Switch mode power supplies seldom get that far. By the time the voltage 
regulation is so far gone as to show a difference on a voltmeter (even 
a Fluke), the box itself has long since given up even trying to run off 
that psu.

The correct test and the only one that is valid, is to observe the dc 
output rails under load on an oscilloscope and look for high frequency 
ripple of the order 20kHz - 200kHz on the lines. If you can see it, and 
the trace is anything but a sharp thin line, the psu needs 
replacing/repairing. Considering the enormous effort it requires to get 
these modern jobs open so you can work on it, it's easier just to 
replace the entire thing.

The voltmeter does give you one valid test - to see if there is any 
output AT ALL. Everything else it tells you is useless.

A staggeringly high proportion of people who should know better will 
(wrongly) try to argue this point.

-- 
Alan McKinnon
alan dot mckinnon at gmail dot com

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