Think I fried my mobo...electrical buzz sound coming from PSU

[DanU]

Burning smells are never a good sign. You might have a fried motherboard, and more specifically , fried power MOSFETs. Take a look at the CPU Power mosfets, the nine small black plastic squares which I have circled in the picture. Do any of them look burned or blistered? Give them the sniff test. Do they smell burned?

[Jfrostt]

Thanks for the reply DanU. I checked every one, they all look perfectly fine, and they don't smell like anything. The only smell on the mobo is a very faint silicon smell near the CPU, probably from the heat dispersed when power went through it - nothing smelling like burning.

I went ahead and ripped apart my old PC which was a PCI-Express 32-bit Pentium 4 (socket 775), and starting mixing and matching pieces to find my problem. The results have left me pretty confused - here they are:

Old PC parts: 450W PSU with a 20pin ATX, Pentium 4 (socket 775) cpu

Test 1) I tried hooking the old PSU into the new PC and nothing happened at all - probably underpowered with only that 20pin ATX.

Test 2) I hooked the new PSU up to my old PC and it booted fine, and posted (no buzzing).

Test 3) My new mobo says it supports Pentium 4's, and supports LGA775 socket, so I put my Pentium 4 cpu into the new mobo. I used the new PSU, and had its 4pin and 24pin ATX's both hooked in, and tried powering it up and nothing happened. I then tried unhooking the 4pin, and only had the new PSU's 24pin ATX hooked in, and it turned on and seemed to be running fine. I then hooked in the video card and a stick of RAM, to see if it would post without the 4pin ATX plugged in, and it still turned on but it did not post.

Test 4) The same as Test3, but with my old PSU. The same effect occurred, where it would only turn on with the 4pin ATX unplugged. So then I tried to see if it would post by hooking in the RAM and video card, with the 4pin still unplugged, and it would not even turn on. I'm guessing the 20pin ATX was underpowered.

Test 5) I tested the video card in my old PC to make sure it was functional, and it posted. I also checked the 1 stick of RAM, and it posted with that as well. I just had to make sure the problem laid within the CPU/Mobo/PSU.

Test 6) With the realization about the system turning on when the 4pin was unplugged, I went ahead and put the Core2Duo cpu back in, and hooked up the new PSU and the 24pin ATX. It would not turn on - but it also did not do the thing it used to with the electric buzz sound and fan twitch. I then plugged in the 4pin ATX as well, and still nothing. Afraid I had damaged it with my Pentium4, I put the pentium4 back in and tried it out again, and it turned on with the results as the last time the P4 was in. Then it occurred to me maybe I had damaged my P4, so I tried that out with my old PC again and it posted. I then went back and tried the new PSU with my old PC, and it still posted.

Then I noticed one major thing after I finished all my tests - the rear fan on the PSU doesn't spin. I'm wondering if the buzzing noise coming from the PSU before was the fan dying? Then again, the noise only happened when it was hooked into the new PC and not my old one. But I also never checked if the fans were working properly until at the very end. Could it have died from some short that's been causing a problem the whole time? Or maybe the buzzing all along was just the fan whining as it died, and it never had enough power to boot the pc?


From my tests, I think I can conclude:
-The RAM works
-The PSU works (broken rear fan?)
-There might be something wrong with my mobo's 4pin ATX plug socket?
-The Core2Duo takes alot more power than my Pentium4
-Maybe the new PSU just isn't pumping out enough power to boot the PC with the Core2Duo E6600?
-Then again, my friend's PC was able to use this new PSU to boot his new computer which uses an E6600 as well, but with a different motherboard - a less expensive one which *might* use less power. This was about 6-7 days ago, and it didn't make any buzz noise with his PC.


I'm really, really confused at this point. The only parts I haven't been able to test in another machine are the CPU and Mobo.

Thanks again for any help!

[DanU]

Wow... I had to read that twice to fully understand all those tests! I'm leaning towards a bad motherboard. I think you've got enough proof to justify an an RMA. Let us know what happens...

[Jfrostt]

Ah, I'm reluctant to do an RMA though since this motherboard is the new one from an RMA already


I'm currently doing all the tests again to make sure my results were right - I'm not ready to give up on my mobo yet.. I'll post the new results as soon as I have them.

EDIT: Ok here are the results:

• E6600....20Pin....4Pin.... Nothing happened at all.
• E6600....20Pin....No 4 Pin....Turned on for 1 second with maybe 10 fan revolutions. It would not do this again until I went and unplugged and repluggin in the 20pin ATX cable.
• E6600....24Pin....No 4 Pin....Same as above - turned on for about a second.
• E6600....24Pin....4Pin....Very short (the sound is back!)
  buzz/clicking noise from the PSU, and fans twitch very briefly for maybe 1/4 a revolution. It doesn't require me to unplug/replug the ATX 24pin cable to reproduce this result.

• Pentium4....24Pin....4Pin....Exactly the same as above, the buzz/click and fan twitches.
• Pentium4....24Pin....No 4 Pin....Turns on and stays on! No hot smells! Rear fan on PSU still not moving though.
• Pentium4....24Pin....No 4 Pin....With peripherals!....Turns on and stays on, but does not post. I tried the RAM in multiple sockets with no success.
• Pentium4....20Pin....No 4 Pin....Same as above - turns on and stays on! When I did the peripherals test, it would not post.
• Pentium 4....20Pin....4Pin....Very faint click noise in the PSU, no fan twitching.

So it seems that whenever the 4Pin ATX connector is plugged in, both PSU's make a click noise, but the newer PSU's clicking is more of an electric buzz and is much louder.

The only times the computer will turn on and stay on is when the 4Pin ATX connector is not plugged in with the Pentium 4 as the cpu. It would start to turn on under these conditions with the E6600, but wouldn only be on briefly which I'm guessing is due to a lack of power from the 4pin ATX not being connected. Also the reason for the Pentium4 not posting could be due to the 4Pin ATX not being connected.

So do you think my motherboard's 4Pin ATX plug socket is broken?

[DanU]

Ok let us know what happens.

Try also checking the 4-pin ATX12V plug for any scorching or burning. Check also the receptacle where it plugs into the motherboard.

[Jfrostt]

I can't see any marks on the plugs or on the motherboard. No smells either. I posted my test results in my post above in an edit.

Thanks again!