PSU and motherboard power problem

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Peter Dalton

Reputable
Oct 20, 2014
2
0
4,510
Hi there,
My computer wont start. It was going fine and then flickered a few times, then stopped. I checked the machine over and noticed there was no power to the MB, no fans and no POST.
I removed the power supply and with a jumper between pins 15/16 the power supply lights and fans work. With the hard drives, DVD drive all plugged in, you can hear the hard drive and fans spin. I checked that I had 12 volts at the 8 pin connector for the CPU. It was ok.
I also checked that the power button was closing the circuit and correctly connected to the jumper pins on the motherboard.
I have checked the CMOS battery and it seems ok giving 3.1 volts.
I have tested the other voltages on the 24 pin connector and they appear fine.
I assume the problem lies with the motherboard not giving a power on signal to the PSU. I assume that this could be caused by a failure on the board, or a short. My next step is to remove the motherboard and attempt to start it up out of the casing.
I would appreciate any other ideas that you may have.
Cheers for now.
 
Solution
Darkbreeze
Seems you have it well under control. There may however be further faults possible with the PSU but I think you're on the right track. Bench the unit and then fully test the PSU. Rarely, but it does happen, the PSU can show correct voltage but when under a load fail to either supply the necessary voltage or short internally under load and shut down due to thermal or short protection. Here are two tutorials, not that you need them, but just in case they might be helpful.

https://www.youtube.com/watch?v=ac7YMUcMjbw

http://www.tomshardware.com/faq/id-1753671/bench-troubleshooting.html
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Darkbreeze

Darkbreeze

Retired Mod
Jun 24, 2014
80,408
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Seems you have it well under control. There may however be further faults possible with the PSU but I think you're on the right track. Bench the unit and then fully test the PSU. Rarely, but it does happen, the PSU can show correct voltage but when under a load fail to either supply the necessary voltage or short internally under load and shut down due to thermal or short protection. Here are two tutorials, not that you need them, but just in case they might be helpful.

https://www.youtube.com/watch?v=ac7YMUcMjbw

http://www.tomshardware.com/faq/id-1753671/bench-troubleshooting.html
 
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Solution
P

Peter Dalton

Reputable
Oct 20, 2014
2
0
4,510
Hi Darkbreeze,
Thank you for your help.
I followed the instructions for the bench test and found the motherboard posted normally. As I started to reconnect devices, I found that when the card reader was inserted, the motherboard failed to start. I disconnected the card reader and everything else worked normally. On further inspection, it appears that someone has spilt a coke or maybe a coffee into the top of the machine as there was residue in the case and around the card reader casing.
I guess it just proves that drinks and computers don't mix very well.
Best regards,
Pete Dalton
 
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