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Misterious fault

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  • Homebuilt
  • Systems
Last response: in Systems
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July 6, 2010 6:50:41 AM

Hi Guys,

I hope someone can help me here. About a month ago my PC stopped. One morning I found it switched off however I left it on the previous evening. I could not switch it on ever since. The symptoms are that the fans move a bit when I push the power switch but then nothing happens. First I thought it was the motherboard so I bought a new one. Same result. Nothing happened. Then someone advised me that it might have been the PSU short circuited in the first time so now it would have killed both of my mobos... Sent everything back to manufacturer and the retailer. Got the new parts yesterday. Assembled the PC again but no joy. Everything is the same, nothing is working. Before I spend more money could someone help me please?

Thanks in advance!

Specs are ASUS P5QD Turbo, Q6600, GeForce 8800GTX, Antec Truepower Trio 650W, Antec 300 case.

More about : misterious fault

a c 122 B Homebuilt system
July 6, 2010 3:13:37 PM

Our standard checklist and troubleshooting thread:
http://www.tomshardware.com/forum/261145-31-read-postin...

Do all the steps.

If no joy, try breadboarding:
http://www.tomshardware.com/forum/262730-31-breadboardi...

I have a paragraph there describing how to build and test a PC In stages.

First step there is strip all the parts out of the case and install just the CPU and HSF, a case speaker, and just the power supply. When you turn on the system, you should hear a continuous series of long beeps. That's telling you that you have no memory installed.

Case speaker, if you do not have one installed:
http://www.cwc-group.com/casp.html

Silence is bad news. Silence means that either the PSU, motherboard, or the CPU is bad. The best way to test the PSU is by substituting a known good one of similar capacity. You can also use either a PSU tester or a digital multimeter to test the PSU. If you 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.
July 6, 2010 7:28:07 PM

jsc, thanks!

I have done few tests and when I removed the videocard, the pc did start. Now I have to try an other one. Hope that's the faulty. Thanks again anyway. I just did not think the videocard can cause this kind of symptoms. Flip, for the money I spent I could have bought a Radeon HD5870... :pt1cable: 
!