Sign in with
Sign up | Sign in
Your question

Did I Fry My Motherboard?

Last response: in Motherboards
Share
November 19, 2010 3:08:58 AM

So I had installed some switches for some case fans and LEDs but since the switch for the LEDs only had 5v to it, it couldn't power the light on the switch. I'm no expert on everything electronics but I have quite a bit of experience so bear with me. I wired over +12v to the input of the switch and the -12 to the ground of the switch (for the light). I didn't think about it shorting out with the +5v but when I switched it on (the LED switch not computer) it shut the computer off instantly. Now, it wont boot. When I go to turn it on the gfx card's fan stays at 100% like before normal POST, but it never posts. The CPU throttling LEDs on the motherboard light up like before a POST and the HDDs spin. I've checked the voltages on the PSU and they're all fine. I've tried simplifying the system but it does the same thing. Please help me! What did I break!? If anything?

More about : fry motherboard

November 19, 2010 7:13:18 AM

This topic has been moved from the section Opinions and Experiences to section Motherboards & Memory by Buwish
a c 156 V Motherboard
November 19, 2010 1:35:05 PM

First of all, you only need about 1.2 - 1.5 volts to turn on an LED.

Second, what on Earth were you doing with the -12 volt output? :o 

If you are lucky you fried your PSU instead of your motherboard.

Time to troubleshoot.

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. We spent a lot of time on this. It should find most of the problems.

If not, continue.

I have tested the following beeps patterns on Gigabyte, eVGA, and ECS motherboards. Other BIOS' may be different.

Breadboard - that will help isolate 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.

Motherboard LED's mean very little. When on, all they are telling you is that the computer os plugged into a live power socket and the PSU is switched.

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 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.

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.

Next time, when you want to do something and you are not quite sure how to do it, ask. One of us can likely same you some time, money, and parts. :) 
Related resources
November 20, 2010 2:15:40 AM

Thanks for all the help, I think I'll try some of these. However I tried my PSU on a friend's similar system and it started it fine so obviously it's not that that's the problem. It my be the MB or CPU. Or RAM. I'll try some more of these and see if I can narrow it down.
November 20, 2010 3:40:42 PM

How could I tell if it was the CPU or the Motherboard. I tried booting without RAM and it didn't work so it's either the CPU or the motherboard. I'll see if I can get a similar CPU to try to test it. Would the MB or CPU fry first if +12v was back-fed into the +5v?
a c 717 V Motherboard
November 20, 2010 4:12:02 PM

What's going on -> NOW?

I would disconnect all of the 'extraneous' 'stuff' until your rig works; meaning -> "nstalled some switches for some case fans and LEDs..."

D/L Memtest and create a bootable CD/DVD {ISO/zip} - http://www.memtest.org/

Please post the following:
MOBO
CPU
GPU
RAM - provide link(s) to you RAM
PSU
November 21, 2010 1:14:08 AM

I've it's not like something is keeping it from POSTing it just doesn't do it. Like everything EXCEPT the CPU is disconnected and it still just tries to POST but the HSF never comes on.
a c 717 V Motherboard
November 21, 2010 10:54:37 AM

Did you breadboard the MOBO {remove from case -> place on cardboard}? A common problem is 'shorting' either from the I/O sheild or stand-ups. Also, a bad GPU or PSU can do exactly the same -> post failure. P55's are notorious for having bent CPU pins, etc...

So IF you want our help - we really need the info requested...
November 21, 2010 9:18:45 PM

I have determined it's the Motherboard that's faulty. I did breadboard it. I've swapped all the parts (RAM, PSU, CPU) with known good ones and it still did the same stuff. There's nothing left to blame except the motherboard. Thanks for all the help, too bad it wasn't something less important.
a c 717 V Motherboard
November 21, 2010 9:35:23 PM

Sorry to hear :(  Hopefully it's still under warranty.
November 26, 2010 1:47:37 AM

Something to add. I believe one of my HDDs my have been killed as well. I had two in the system, both connected to the PSU and MB, but after this all happened one of them (the main boot drive) doesn't seem to turn on or get recognized by the BIOS in a different system. However when I tried the second HDD from the fried machine in the good machine, it started up just fine and recognized it. This system usually runs on Linux (if that matters). It seems like if the PSU was going to fry the one HDD it would do the same to the second.
!