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  Computer will not power on 
 Date Written 
Gregg Hill Mar 16, 2013, 09:45pm EDT Report Abuse

I suspect that I have a bad motherboard on a friend's computer. The computer is a clone built with an Intel D946GZIS motherboard, SuperTalent 1GB memory, Pentium CPU.

The computer just stopped turning on one day. I used a Coolmax power supply tester very simliar to this one and it showed "HH" on the Power Good signal. I connected a new CoolerMax power supply to the tester, and all shows good. I connected it to the motherboard, got the little LED on by the 24-pin connector, pushed the power button, and NOTHING.

I checked the power button and it is good.

I jumped the Power Switch pins on the board and still nothing.

I jumped the Power On pin to ground in the 24-pin connector, and the CPU fan comes on, but as soon as I remove the jumper, it turns off again.

I checked the voltage from Power On pin to ground, and it stays at 3.93 volts when I push the power button or when I jump the Power Switch pins together.

I **assume** that the Power On pin should drop to near zero when the Power Switch pins are jumped together, and the fact that it never drops is what keeps it from starting.

After that, I am lost as to what to check next.

Did I miss a simple step, or did I confirm that the board is bad?

Thank you for your help!


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Rhort Mar 17, 2013, 05:03am EDT Report Abuse
>> .
Strip the machine right back; take *EVERYTHING* off the board except the CPU (and cooling solution) and one single stick of RAM. When you power up, hopefully it should give you the 'I have no video card' beeps. If you don't get even that, then you *MIGHT* be looking at a bad board :(

If it works at this point, start reconnecting components, one at a time (start with the video card ;) ) until it stops again, then you've probably identified the faulty item.

~ The manual said "Requires Windows '95 or better" I installed Linux!
Gregg Hill Mar 17, 2013, 02:10pm EDT Report Abuse
>> Re: Computer will not power on
#1: I like your "95 or better" tag line!

#2: The only thing I had connected when testing was the CPU and a stick of memory. Tried it without memory, too. All cables other than the 24-pin and the 4-pin 12V for CPU were disconnected. I pulled the CPU, cleaned the top and the cooler's mating surface, put more heat-sink compound on it, and re-installed it.

I think the key is that the Power On voltage does not drop at all even when shorting the board's pins together to simulate the power button being pushed.


Rhort Mar 17, 2013, 03:41pm EDT Report Abuse
>> .
How about a CMOS short to reset the BI/OS? Could be something jamming up the POST.

I certainly think you've covered the bases with everything else.

~ The manual said "Requires Windows '95 or better" I installed Linux!
Gregg Hill Mar 17, 2013, 03:52pm EDT Report Abuse
>> Re: Computer will not power on
Oops, I forgot to mention that one. Yes, I tried that also.

The root must be the failure to drop the Power On voltage. I have not tested a known-good system to see what its voltage does when shorting the power switch pins, but I assume that drops the Power On voltage to near zero, which then triggers the board to start up.

I don't know the whole process of what happens after that step, i.e., once the power button is released, does the Power On voltage go back up? Does something on the board hold it down so the system stays on?

Now I have piqued my interest...dang. I will test a known-good system so that I can understand the POST behavior.

Thank you for your help!


Gregg Hill Mar 17, 2013, 04:12pm EDT Report Abuse
>> Re: Computer will not power on
Interesting. On a known-good system, the Power On voltage is 4.80 volts, and when the power button is pressed, it drops to and STAYS at 0.02 volts. Once the power button is pressed again during POST, it goes back up to 4.80 volts and shuts off the computer. If I let it fully boot, the voltage stays at 0.02 volts until I tell the OS to shut down, in which case it goes back up to 4.80 and shuts down.

That behavior is what I suspected should happen. Now I wonder if I can make a jumper circuit for this computer to short Power On to ground to make it stay up until we can afford to buy a new system.

EDIT at 2:16PM: Tried the jumper of Power On to ground. Fans come on, but nothing else. No video, no beeps, nada! Oh well, it was a valiant attempt.

Rhort Mar 18, 2013, 04:42am EDT Report Abuse
>> .
I'm wondering if forcing a reducing in resistance like that won't blow another component somewhere down the line(?) It's going to be doing that for a reason, which could be an error triggering it deliberately, or something failed that's just caused that to happen at random; either way, sidestepping it could be risky.

~ The manual said "Requires Windows '95 or better" I installed Linux!
Gregg Hill Mar 18, 2013, 10:50am EDT Report Abuse
>> Re: Computer will not power on
I yanked the drive and put it into another system until we can get a new computer.

Thank you for your help!


Rhort Mar 18, 2013, 03:53pm EDT Report Abuse
>> .
Sounds like the best plan. Let us know if you get any further issues.

~ The manual said "Requires Windows '95 or better" I installed Linux!
Naveen Goud Mar 19, 2013, 06:12pm EDT Report Abuse
>> Re: Computer will not power on

Problem seems to be in motherboard. May be a circuit break has happened on your MOBO. Humidity can make things difficult for the motherboard. Once, the same thing happened to my desktop and after almost one day of struggle, i took it to the professional. He confirmed that there was a short circuit in the motherboard as power was reaching the USB, but not the processor. He blamed wet weather conditions for such problem.







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