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PSU issues

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bigchieftaco

Limp Gawd
Joined
Feb 9, 2010
Messages
398
I got a Toughpower 700w modular PSU from my buddy today. He got it on junk days and couldn't get it to work, but then later found out the mobo was junk he was trying it on.
I am now trying to get it to work but same issue. It wont turn on. I took the 24 pin connector off the mobo and noticed it was missing a pin, after some research apparently some PSUs dont have it.(-5v Pin) I disconnected all cables from my mobo and shorted the green pin and a ground pin out and it turned on just fine, seemed like no problems.
Why can't my mobo turn this on? What would cause this?
 
Some motherboards are simply incompatible with certain power supplies for whatever random unknown reason it might be. This has been known to happen.

Is your power switch connected properly to the motherboard? I know it's a basic question, but it has to be asked, and some people do occasionally overlook these things.

What is the motherboard model you have? The other possibility you have is a dead motherboard.
 
I don't think its the mobo, just got it in the mail from a [H] member. I will be testing it sometime this weekend with a different PSU. The mobo model is Gigabyte GA-MA78LM-S2H.

As far as the power switch is concerned, I even disconnected it and tried to short the pins on the motherboard out but no avail. That's why I am so confused because when I take the PSU and short it out with a wire it turns on fine, but when I short the motherboard pins out, nothing.

Does the motherboard have a built in error detection or something because I remember my friend telling me that he used a PSU tester on it and it told him it was low on a certain volt. I asked him about it and he said once he plugged in the CPU power with the 24 pin power the tester worked fine so I didn't think too much about it.
 
bigchieftaco said:
I don't think its the mobo, just got it in the mail from a [H] member. I will be testing it sometime this weekend with a different PSU. The mobo model is Gigabyte GA-MA78LM-S2H.

As far as the power switch is concerned, I even disconnected it and tried to short the pins on the motherboard out but no avail. That's why I am so confused because when I take the PSU and short it out with a wire it turns on fine, but when I short the motherboard pins out, nothing.

Does the motherboard have a built in error detection or something because I remember my friend telling me that he used a PSU tester on it and it told him it was low on a certain volt. I asked him about it and he said once he plugged in the CPU power with the 24 pin power the tester worked fine so I didn't think too much about it.
Click to expand...

If one of the rails really is low, then the motherboard would refuse to turn on due to insufficient voltage. Check out the rails with a DMM.
 
PSU testers are generally not particularly accurate. If you have access to a digital multimeter, use that to check the voltages. I can provide instructions on how to do this if you need them. The acceptable limits for the rails are 3.16-3.49V for the +3.3V rail, 4.75-5.25V for the +5V rail, and 11.4-12.6V for the +12V rail or rails. Keep in mind that if the voltages are only slightly out of these ranges, the motherboard should still function. They would have to be very low to prevent it from working.
 
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