How to test PSU with the multimeter?

Astralv

Distinguished
My one year old build with Haswell processor and Solid Gear SDRG-750E power supply suddenly stopped working. It is not able to post. The fan on the power supply is spinning, the fans on the case are spinning, but the red lights on the motherboard for memory, CPU and VGA are blinking and it is not able to load BIOS. I don't know what next step to take in solving it and want to test the power supply. I have multimiter but I can not find any information on how to test the power supply. Let's say I unplug it from the motherboard and I have 24 pins (20+4). It is not labled to know what to test with what. Please, advise. Thank you
 

Astralv

Distinguished
This is helpful, thank you very much. We not getting any reading. How do we supposed to test it? I unplugged 20+4 connector from the motherboard, I have PSU switch on and I test by putting multimiter probes in to the pinholes. Nothing. Am I doing something wrong? I want to believe it is $50 PSU problem and not $350 processor problem, but should there be any electricity if it able to light the fans and led lights on the motherboard- I get nothing at all.
 
Although testing of the PSU can be of some use while disconnected from the motherboard and other loads, it is preferred that the PSU be connected and switched on (loaded) so that other faults can be detected. In this case measure the voltages from unused connectors.

Note that not all faults can be detected using the basic multimeter test procedure, some faults may require specialized equipment in order to detect these faults.

Another way to test the PSU is to install it in another computer (friend, neighbour etc computer if necessary), and/or try another known working PSU (borrow one if necessary).

EDIT: To test the PSU whilst disconnected from the motherboard (and with the PSU switched off for the moment), short out pins 16 & 17 of the 20/24 pin main motherboard connector using a paperclip or short wire etc,, then switch on the PSU.
 

clutchc

Titan
Ambassador
+1^
I presume you have the PSU connected to the board and powered up when testing. If so and if you are sure your probes are making good contact, it appears the PSU is defective.

Note: always pre-test the multi-meter on a known live circuit first to be sure it is working.
 

Astralv

Distinguished
I pretest multimiter on AA battery and it shows 1.49V, so looks like multimiter is ok.

If I have PSU connected to the board, then how can I test the pinholes? No, I have PSU disconnected from the board, I am holding the 20+4 connector in my hand and putting the probes in to the pin holes. Is it how it done? Thank you.
 

Astralv

Distinguished
Ok, so I am testing unused Molex cable while 20+4 cable is connected to the motherboard. On the molex I do get 12 V and 5 V. Does it mean- the PSU is ok?

I wish it was not ok, but I guess I am to proceed with testing the motherboard. I posted another thread under motherboards forum, asking how to test the motherboard, if you have any thoughts, please, post them here: http://www.tomshardware.com/answers/id-3074771/test-motherboard-working.html
 
Testing motherboard is not really an option as it usually requires specialized equipment to do that.

Test as many unused connectors as possible. It is possible that part of the PSU is working fine, but some other parts may be faulty.

It is recommended that the PSU be tried in another computer, and/or another known working PSU be tested. This is the best way to determine whether the PSU and/or the motherboard may be faulty without having to use special test equipment.
 

Astralv

Distinguished

Thank you for your reply. I was able to test at least one Molex connector, but I don't know how to test SATA style connector (the one that connects to HDD or SSD) as it covered in plastic.

It would be hard to unplug PSU from another computer. Not impossible but would require disconnecting all DVDs, SSDs, HDDs, motherboard, graphic card, and then move it to the broken build... or to buy another PSU- spend at least $80 just to see if it would work better...

There has to be a way to test 20_4 pins port, but when it not connected to the board I get no reading.
 
To test the PSU with the wires/connectors removed from the motherboard -

Switch off PSU

Remove all connectors from the motherboard that come from the PSU.

Insert a paperclip, or short piece of wire, or similar metal object/conductor across pins 16 and 17 within the 20/24 pin connector to short out those pins. Pin 16 might have a green wire coming from the connector, and pin 17 should have a black wire coming from the connector.

Switch on the PSU and then measure the voltages at the 20/24 pin connector. Refer to the diagram of the connector which clutchc indicated earlier.


Again, as mentioned already, this measurement of voltages of the PSU while disconnected from the motherboard is not entirely foolproof; it wont pick up some faults. For that reason, it is still recommended that this PSU be tried in another computer, and/or another PSU be tried despite any inconvenience in having to disconnect/reconnect cables etc.
 

Astralv

Distinguished

Ok, I guess I know what I am doing tonight... :(

Thank you. Will update.

 

clutchc

Titan
Ambassador


You can stick the pointed tip of the probe into the back side of the 24 pin connector while the PC is on. I do this often.

You can also jumper the green and any black wire on the 24 pin connector to turn on the PSU, if you don't want to test the 24 pin connector with it plugged in and the PC on. The green and black has to be jumpered before the PSU will turn on.
 

Astralv

Distinguished


What do you use to jumper?

Thank you.
 

clutchc

Titan
Ambassador


Anything that will stick in the connector. A paperclip is the usual item folks use. But I always grab one of my small alligator clip jumpers. There's no voltage to be worried about with those two pins. It's just a grounding signal to tell the PSU to turn on.
 

Astralv

Distinguished


Do you mean bent paper clip that would go from hole with green wire to hole with black wire? It unconnected 2 different paper clips for each hole? Thank you.