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Is my mobo or my CPU dead?

  • Asus
  • Motherboards
Last response: in Motherboards
November 21, 2010 12:57:08 AM

today, about a month after i built my first computer, i stupidly was fiddling around with a cable that kept touching a fan with the computer on. another wire with metal tip slid across a pci slot, which i think shorted it out. the screen went black and the led on my mobo lit up telling me the cpu had a problem. all the fans, lights, and hard drive were still on. frightened,i pressed the power button with no response, so i had to flip the master switch on my psu. when i flicked it back on, the power buttons flickered on for a fraction of a second and then died before i could turn it on. i tried clearing cmos, which creates a response, but the power buttons, even direcly on the mobo, don't work. i tested the psu and it works fine, so now i need to know which is the culprit- my mobo or my cpu

parts: Asus P7p55d Deluxe
I7-870 OC'd to 3.8ghz
Corsair TX650w

Any advice or help is appreciated

More about : mobo cpu dead

a b Ĉ ASUS
a c 156 V Motherboard
November 21, 2010 1:46:48 AM

How did you test your PSU?

Work through our standard checklist and troubleshooting thread:
I mean work through, not just read over it. We spent a lot of time on this. It should find most of the problems.

If not, continue.

I have tested the following beeps patterns on Gigabyte, eVGA, and ECS motherboards. Other BIOS' may be different.

Breadboard - that will help isolate any kind of case problem you might have.

Breadboard with just motherboard, CPU & HSF, case speaker, and PSU. You do have a case speaker installed, right? If not, you really, really need one. If your case or motherboard didn't come with a system speaker, you can buy one here:

You can turn on the PC by momentarily shorting the two pins that the case power switch goes to. You should hear a series of long, single beeps indicating memory problems. Silence indicates a problem with (in most likely order) the PSU, motherboard, or CPU.

Motherboard LED's mean very little. When on, all they are telling you is that the computer os plugged into a live power socket and the PSU is switched.

Remember, at this time, you do not have a graphics card installed so the load on your PSU will be reduced.

If no beeps:
At this point, you can sort of check the PSU. Try to borrow a known good PSU of around 550 - 600 watts. That will power just about any system with a single GPU. If you cannot do that, use a DMM to measure the voltages. Measure between the colored wires and either chassis ground or the black wires. Yellow wires should be 12 volts. Red wires: +5 volts, orange wires: +3.3 volts, blue wire : -12 volts, violet wire: 5 volts always on. Tolerances are +/- 5% except for the -12 volts which is +/- 10%.

The gray wire is really important. It should go from 0 to +5 volts when you turn the PSU on with the case switch. CPU needs this signal to boot.

You can turn on the PSU by completely disconnecting the PSU and using a paperclip or jumper wire to short the green wire to one of the neighboring black wires.

This checks the PSU under no load conditions, so it is not completely reliable. But if it can not pass this, it is dead. Then repeat the checks with the PSU plugged into the computer to put a load on the PSU.

If the system beeps:
If it looks like the PSU is good, install a memory stick. Boot. Beep pattern should change to one long and several short beeps indicating a missing graphics card. Silence or long single beeps indicate a problem with the memory.

Insert the video card and connect any necessary PCIe power connectors. Boot. At this point, the system should POST successfully (a single short beep). Notice that you do not need keyboard, mouse, monitor, or drives to successfully POST.

Now start connecting the rest of the devices starting with the monitor, then keyboard and mouse, then the rest of the devices, testing after each step. It's possible that you can pass the POST with a defective video card. The POST routines can only check the video interface. It cannot check the internal parts of the video card.
November 21, 2010 8:46:53 AM

Don't think its the CPU... Cpu is normally the last thing that crashes because of power.. but it could be :S
November 21, 2010 3:28:57 PM

"another wire with metal tip slid across a pci slot, which i think shorted it out. the screen went black and the led on my mobo lit up telling me the cpu had a problem"

Was there any sparks at all, and did this all happen as soon as it touched. If so I'd put money on the mobo. Of course only way to really find out is to test all pieces seperatly of each other.