Here is how to test a PC power supply.
What you need:
- a paper clip
- a multimeter to measure volts DC current
How to do it:
- ** disconnect power supply from wall AC outlet
- no need to remove power supply for computer case (this is optional)
- disconnect all power connections inside your computer case that come from the power supply. It isn't hard to remember where things go. They can only plug in one way. You can't mess it up. Disconnect power from; motherboard, CPU, CPU fan, case fans, drives, video cards etc. Basically if a cable comes out of the power supply follow it and disconnect it. Document it with photos before disconnection if it makes you feel better to then review for later reconnecting.
- open up paper clip and make a big U shape with it.
- find the large long motherboard power cable connector that your disconnected. The one with 24 connection points.
- on this large power cable connector locate the one and only green cable point.
- insert opened up U shaped paper clip into the green and any black connection points. This is safe. You can use your hands. No shock will result.
- ensure that you lay down this now inserted paper clip so that it doesn't touch anything metal.
- insert AC power cable to wall outlet for the power supply
- ensure that the PC power supply has physical switch turned on if it has a physical switch. This would be located near where you plug in the AC cable. Again not all power supplies have this switch.
- the power supply should now be on. The internal fan of the power supply should be spinning.
- if smoke or sparks occurs immediately disconnect AC power cable from wall.
- if fan is spinning you are now read to test voltages with multimeter.
- test for voltage on one of the small drive power lead wires. Test for 5 volt and 12 volt DC separately. First test black and yellow for 12 volts and then black and red for 5 volts. You can also check for 3.3 volts by testing orange and black on the motherboard connector.
This is a good test that anyone can do. Even if you don't have a multimeter you can test if the power supply turns on and starts its internal fan which that in itself may be more than you get with your computer's power button. If the fan turns on in this manner but not with the PC button then that right there is a good sign that the motherboard is the problem.