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Motherboard or CPU?

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August 26, 2010 1:57:12 AM

I'm new to the techworld and need help. My girlfriend desktop (HP Pavilion a1540n not supported by manufacturer anymore, built in 2005) simply stopped turning on. There is no lights, no beeps or whatsoever signal of life. I thought it was the power supply, I tested a connector and the readings were +8 v where was supposed to be +5, and 13 where was supposed to be 12, but still granting power. The power switch seems OK, so, my doubt is if the motherboard went bad or could be the CPU. I think about the CPU because I had replace the cooling fan without adding cooling paste to the much it was before that, taking a chance for overheating. Any idea? I will appreciate it.

More about : motherboard cpu

a b à CPUs
August 26, 2010 2:15:14 AM

CPU's VERY rarely are the problem, it is 90% of the time HDD, PSU, or MOBO. CPU's have a very hard time failing. If no lights come on, well light should come on on the MOBO when you turn power on, whether the computer works or not. Id check that out first.
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a b à CPUs
a c 136 V Motherboard
August 26, 2010 9:32:14 AM

I agree, check if any lights come on on your motherboard when the power is on, if it doesn't show any lights, then your motherboard has probably failed.
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a b à CPUs
August 26, 2010 10:21:39 AM

Yes, it's probably the mobo (though it maybe the PSU's fault). And check all the cables that go throughout the PC case.
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Best solution

a c 172 à CPUs
a c 156 V Motherboard
August 26, 2010 10:38:40 AM

Work through our standard checklist and troubleshooting thread:
http://www.tomshardware.com/forum/261145-31-read-postin...
I mean work through, not just read over it.

Breadboard - that will eliminate any kind of case problem you might have.
http://www.tomshardware.com/forum/262730-31-breadboardi...

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:
http://www.cwc-group.com/casp.html

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. 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. 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.
http://www.youtube.com/watch?v=5FWXgQSokF4&feature=yout...

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.
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a b à CPUs
a b V Motherboard
August 26, 2010 3:00:15 PM

The symptoms indicate a motherboard problem. If it was the CPU it would turn on, lights and fans, but not POST and may not even beep. Of course, I'm sure that not putting on fresh thermal grease was no help so who knows if the CPU got taken out as well when the motherboard went :D .

Look, if it uses DDR2 RAM, just get a cheap AMD motherboard/CPU combo (with a decent motherboard of course). Even the lowly Athlon II 240 would be a significant upgrade to the older Athlon 64 or X2 it likely comes with.
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a b à CPUs
a b V Motherboard
August 26, 2010 3:01:47 PM

Of course, if the CPU does work (you say you upgraded it but you didn't say to what) you could just buy a good motherboad, overclock it, and get a speed upgrade for free :D . Of course, that's assuming that CPU still works.
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August 30, 2010 1:57:09 AM

Best answer selected by Uriel Algaba.
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August 30, 2010 2:05:32 AM

Thanks all guys. The only thing didn't work on PSU was the negative voltage, recalling the +5 read +8.3 and the +12 read +13. However, your feedback lead me to my intuition: the motherboard. Thanks.
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