Electronics

Electronics

Κυριακή, 19 Απριλίου 2015

Repair A Power Supply of A PC

A few days ago a friend of mine gave me a fault power supply, which he was going to through away. I tooked it from him and I repaired it. In most cases of a pc power supply the problem may be occured due to false capacitors which are the first parts to show some damage in a period of time. One big advantage if a capacitor is false it's that you can see it immediatelly (mostly!) without a special meter, because a blown capacitor looks different from a good capacitor. Precautions must be taken in case a capacitor still is charged because you might have a good zap! Measuring the voltage across their legs and discharching through a 5W - 1KΩ resistor is a good solution. Opening the case I was lucky to find quickly the two bad components. Unfortunatelly I didn't took a picture from them when they were on board but afterwards.




The capacitors where positioned in the corner left, as you can see from the pictures the difference between 2 fault capacitors and 2 good capacitors are visually easy. Pay attention to capacitance ratings and voltage ratings, The ones you change should be same capacitance and if not same voltage, then bigger. If they are bigger voltage pay attention because the size of capacitors increases too and it will need some extra effort putting it back to the board. Next step is to download a schematic with all the wires and their names (voltages) connected to the 24-pin clip or 20-pin clip. (In my ocassion 24-pin).





As we can see there is a pin named "PS_ON#"  (in most cases it's green) and this one should be connected to ground if we want to power on our supply without connecting it to a load (e.g. the pc).


Next step is to measure all the voltages according to the above schematic, so these are the values we should take from every pin. :  +3.3 Volts,   +5 Volts,   +12 Volts,    -12 Volts. Colors of cables should be different but in my occasion 3V3 was orange, 5V was red, +12V was yellow, -12V was blue and Ground was black.



If all voltage pins are the same with the schematic above, then you are set to go with a new power supply!

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