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 -- [email protected] mailing list
