Testing computer desktop power supply?

Hello all, I am learning to use a multimeter to test the different voltages of a PC Power supply unit connector, I am working with a 20-pin connector, first do I need to use the paper clip to short the green and black wires to test the voltage outputs? If not, I have placed the black probe into pin15 and the red probe into pin11 with the multimeter set to 20 on the V section as shown by the red arrow in the attached pic and I am not getting any reading on the meter?

This is a link to a screenshot of my settings on the MM, the red arrow shows where I have set the voltage but I am not sure if it's that volatge setting or the other one below?


and this is a link to a better close up view of the exact MM I have, please use the enlarge tab to see it more close up? Thanks.

10 answers Last reply
More about testing computer desktop power supply
  1. yeah, the green has to be shorted to ground. once that happens, the psu will turn on.
    just curious, what are you using it for? just electronics experiments? I've done this to a few psus and they're pretty ok for the job as long as you get them for cheap/free.
  2. Thanks and sorry for the late reply. I am doing this to get the experience on properly testing a PSU before condemning it. Ok, I have shorted pin14 [green] and 15 [black] so the fan is spinning but according to the tutorial I had referenced to here:


    The instructions are:
    Turn on your multimeter and turn the dial to the VDC (Volts DC) setting.

    Note: If the multimeter you're using does not have an auto-ranging feature, set the range to 10.00V.

    First we'll test the 24 pin motherboard power connector:

    Connect the negative probe on the multimeter (black) to any ground wired pin and connect the positive probe (red) to the first power line you want to test. The 24 pin main power connector has +3.3 VDC, +5 VDC, -5 VDC (optional), +12 VDC, and -12 VDC lines across multiple pins.

    First issue, I am seeing 2 V settings as my screenshot in earlier post shows, which is the correct section, the top which shows the Vm on top or the section below which shows the V and that other sign? Also, should the setting be on the number 20 since I first wish to test the 12 volt or the number 2?
  3. OK. You need the 20v setting. The meter is always set larger than the quantity you are measuring. Also, make sure you are using the correct plugs on the meter. One for common and one for the volt meter / ohm meter.
  4. Also, you use the section with the solid line above the dashed line. That stands for DC.
  5. misclik said:
    Also, you use the section with the solid line above the dashed line. That stands for DC.

    Sorry I don't understand. Can you tell me from the screenshot in my OP if it's the one showing with the red arrow or the other section below please?
  6. Yeah red arrow
  7. Thanks, so if I am testing correctly, I placed the black probe from the COM port on the MM into the black wire pin 13 and the red probe from the volt/ohm port into the orange wire pin 11, the MM reads 0.64, is this correct procedure and answer please?
  8. Correct procedure, bad reading. Psu could be dead. Obviously you're doing that while the green is shorted to a black, right?
  9. Yes, the green and white is shorted with a paperclip. I also placed the black probe into pin7 [black wire] and the red probe into pin8 [grey wire]and the MM is showing .78? I then did the same testing with another identical PSU and the reading this time was .83? I then tried black probe into pin7 and red probe into pin10 and I am getting 2.02?

    I don't understand what's going on here because these 2 PSU's were pulled from working systems so I am wondering if my testing procedure is wrong?
  10. OK. If you have scissors and wire strippers, use them. You need to short the GREEN to BLACK. then put the black lead to a black wire. Then you will get the voltage of any other wire with respect to the black lead. If anything, look on youtube . There has to be a video on how to use a dmm.
Ask a new question

Read More

Power Supplies Desktops Computers Components