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PSU bench power supply Answered

My PSU appears to have blown up over the christmas holidays- it was a bit unreliable before, but now it won't boot up my computer at all. I replaced it with a spare from work which works fine, so I now have a not-working 400W PSU I'd like to make a bench power supply from, that will hopefully kick-start my desire to get into microcontroller programming. Does anyone know what the chances are that a broken PSU (no sign of magic smoke, it just doesn't power my computer any more) will still be working enough to use as a DC power supply? If it is, the 'Ibles sometimes disagree- what is the accepted way of keeping it turned on (short a pair of wires, attach a resistor across a pair etc)? It's a 20-pin connector with square 4-pin aux and the usual complement of molex.


its very often capacitors. open it and look for capacitors with blown top or that look bad in another way replace them with same value capacitors (for the larger capacitors on the output you can use larger capacitors too) dont mess with it (keep it for spare parts) if there is anything burned on the high volt side (before the txformers) or in the control system (the small components around the chip in the low voltage side) if it won't start at all and there are no visible burned components inside (ie its safe to plug in) you usually can still get 5 V 1 A from it (the 5 V stand by entry) to power on the supply connect the green wire to black the 5 V stand by output is allways on as long as the supply is plugged in. its + on violet and - on black this is ok for most 5 V circuits (like micro controllers) and great to replace most 6 V (and sometimes 4.5 V) wall txformers (it can be >2 X more efficient and wastes less electricity) some manufacturers substitute wires with wires of other but close color. the wires next to the green from 3 sides are red and 2 blacks. the violet wire is next to the yellow wire after you fix the supply let it run few hours without load and then with load ad see if voltages are correct and stable if its only bad capacitors on the secondary (and no overheat signs etc) you have good chance that the capacitors are all the problem. if you replace them the supply might be appropriate for computer again. i use mostly such supplies with replaced capacitors in my computers

Also power transistors can fail and are easily replaced. Common issue on many things, driver modules for the lights in monitors often can be revived.

Somewhere it is discussed that a computer power supply is a switching power supply. That means is needs some kind of controller circuitry or something to keep it turned on. You'll have to look it up. Good luck.