Please help with motherboard issue

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alfredpg

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Oct 23, 2011
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Hi:

I own an ASUS M3N72-D motherboard for my AMD Phenom II X4 940 BE processor, and I recently sent the motherboard to ASUS for repair because it was not working. The green light that is supposed to be solid green on the motherboard was flickering, and the motherboard would simply not power on. At first, I thought it was the PSU, but after testing (used a multimeter to ensure it was fully functional, and attempted to power on the PSU without the motherboard using the 15th and 16th pins on the 24-pin connector) I found that the PSU was fully functional.

I tested the motherboard with nothing but the CPU and two sticks of RAM, then one stick of RAM, then nothing (no cpu or ram). All of these resulted in the flickering green light which was not allowing the motherboard to power on. During original testing, with the motherboard still in the case, my cousin and I were just turning the power on and off to see if we had any luck and the entire computer including the motherboard powered on ONCE with no RAM, but everything else on (CPU, GPU, soundcard, heatsink). It gave me the usual beeping noise to tell me there was no RAM, and after we turned it off to try and see if it worked again, it discontinued working. We tried with no RAM several times, thinking it was the RAM but to no avail.

After sending the motherboard to ASUS and explaining the problem to them, they were able to "repair" it in just a few days and I just received it back today. It still has the same exact issue. I have contacted them and they are putting me through a process where they'll check their stock to see if they have my motherboard in one of their facilities and they will then send it to me.

Am I missing anything here? If the motherboard was fully functional and it was indeed my CPU (which makes no sense to me since it turned on that one time) would the green light be solid without the CPU on? The CPU appears to have no physical damage and no signs of overheating.

Any help would be great,

Thanks in advance.

edit: typos

One quick note I didn't mention: the computer in question was unused for a little under a year. I did not clean it until last week when I was testing everything. There was accumulated dust on the motherboard, but I dusted it all off using compressed air. Is it possible the motherboard short-circuited during that process? Unfortunately I do not have another motherboard to test any of my components on, or this would be far easier. However, everything did work the time it turned on.
 
Solution
mavroxur




Three possibilities that come to mind:


1) The power supply is powering on under no load (by shorting pins 14+16 (green wire to black wire)), but when a load is applied, the PSU is failing to start. I'd try a different power supply from a known working system.


2) Something in the case is shorting out the board when it's installed. Try powering the board up outside the case on a non-conductive static-safe surface surface (lay it on an antistatic bag) with minimal components.

3) The board is bad.
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I think you have a PSU problem. What kind of PSU? How did you test the PSU?

The flickering green LED on the motherboard is illuminated by the standby power supply, a small completely independent, always on, 5 volt power supply labeled 5VSB usually, output is on the violet wire.

Here's some more detailed instructions about how to check a 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.
 
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Three possibilities that come to mind:


1) The power supply is powering on under no load (by shorting pins 14+16 (green wire to black wire)), but when a load is applied, the PSU is failing to start. I'd try a different power supply from a known working system.


2) Something in the case is shorting out the board when it's installed. Try powering the board up outside the case on a non-conductive static-safe surface surface (lay it on an antistatic bag) with minimal components.

3) The board is bad.
 
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Solution
Thanks the responses.

@o1die: The problem is not that the motherboard does not work with the power supply, as I used it for a year with no problems. It is a Thermaltake ToughPower 750watt.

@jsc: I used a multimeter and it showed 5volts, so I figured the PSU was not the problem. I also powered the PSU on without the motherboard, and it turned on the fans, LED's etc without issue. I used the green&black wires on the 24-pin to do that. I will use the multimeter to measure the other wires since I haven't done that yet.

@mavroxur: Those are some interesting ideas about it not starting when a load is applied.. I will try the motherboard with another PSU soon. I took the motherboard out of the case as soon as it stopped working and used an antistatic bag and still no luck either. IF it was the PSU, it would explain why ASUS sent it back so quickly, but I'm still confused about why they're deciding to send me a new one.

Thanks again.

edit: typos -.-
 
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It it was your PSU, that's why the sent it back so quick. The board might be good after all.
 
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