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Mobo shorting out?

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September 8, 2010 6:47:52 PM

Built a new desktop system about two months ago, everything had been working fine. Yesterday it shut down immediately and would not turn back on. At first I thought it was a bad PSU, but after testing, it powers everything just fine - except when the video card is plugged in. So I thought it was a bad card, and I exchanged it for another one. After installing the new one, I was able to boot but then it shut down after about 5 minutes. Then I thought it was a heating problem. Tried a new fan, but the PC still would not boot. Tried the video card in another slot, same problem.

Everything works when there is no video card. Once I plug it in, fans spin for about one second and everything shuts down. Any suggestions?

Specs:

Windows 7 x64
CPU - AMD Phenom II X6 1055t
Mobo - Gigabyte 890XA-UD3
RAM - 4GB OCZ DDR3 PC3-1066
Video card - Radeon HD 5500
HDDs - Barracuda 7200 SATA 280GB, WD Caviar Green SATA 500GB
PSU - OCZ ModXStream 700W

More about : mobo shorting

a b U Graphics card
a c 108 V Motherboard
September 8, 2010 7:35:22 PM

Welcome Newcomer. Your post does suggest your mobo is shorting. Try breadboarding to rule out any problems in the case.

You should also go through the troubleshooting checklist, just to ensure you've ruled out other possibilities.

Follow the link in my signature to jump to the t/s guide. At the end of the guide, you'll find a link to jsc's breadboarding tips.

Good luck.
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a b U Graphics card
a c 716 V Motherboard
September 8, 2010 9:09:49 PM

Hmm, dual rails - do you have a DVM {digital voltage meter ~ $25} to test the PSU? Meaning if (1) rail is dead/shorted internally powering the GPU then you'll have as you described. Any odd smells?

I doubt that you "suddenly" developed a "mounting" short overnight, but it is possible. Instead of bread boarding a quick way is to unscrew the mountings and pull the MOBO away from all mountings and see if it will turn-on while "dangling."
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September 8, 2010 9:19:38 PM

T_T said:
Welcome Newcomer. Your post does suggest your mobo is shorting. Try breadboarding to rule out any problems in the case.

You should also go through the troubleshooting checklist, just to ensure you've ruled out other possibilities.

Follow the link in my signature to jump to the t/s guide. At the end of the guide, you'll find a link to jsc's breadboarding tips.

Good luck.



I agree with T_T sounds like a motherboard issue.
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a b U Graphics card
a c 156 V Motherboard
September 8, 2010 9:26:47 PM

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.

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.

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September 8, 2010 10:07:45 PM

Thanks, jsc, yeah I went through that linked checklist when I first built the machine. Great guide. I was able to exchange the board for another one and I've installed it but it will not post, so I'll go through the checklist again.

One question about the standoffs - I tried them in my case when I first built my machine and the motherboard would not fit. So I never used them and had no issues until the present problem. The case is a no-nonsense mid tower which has, I don't know what you call them, raised beds on the side of the case for the motherboard screws. The case came with one brass standoff in the middle, and that's no problem. But if I put standoffs in those raised bed screw holes, the motherboard is that much higher off the side of the case, and like I said, it won't fit. Am I OK without these things, or could that be the issue?
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a b U Graphics card
a c 716 V Motherboard
September 9, 2010 12:32:28 AM

You always need to remove/move so the only "standoff's" align with the MOBO's screw holes. If I read correctly, there are "standoff's" of varying height use the correct height or find replacements.

Again, what you described seems more like a PSU issue; @coloneltravis "I was able to exchange the board for another one and I've installed it but it will not post"

The problem with a paperclip is it works, sort of, with a single rail PSU. So either try another PSU or DVM. Alternatively, it's the CPU.

Good Luck!
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September 9, 2010 1:48:17 AM

Here's a photo of my case:

Uploaded with ImageShack.us" alt="" class="imgLz frmImg " />

You can see 5 of the raised screw beds. I don't think standoffs exist that are short enough to go in those raised screw beds and still allow the board to fit correctly. At that point the board is about half an inch off the side of the case and nothing lines up in the back. The bottom of the board is not going to touch any part of the case, because each raised beds is as high as a standoff is. The reason I asked is because those raised beds are still part of the case metal. I didn't know if the brass served as some kind of insulator, or if they were used just to keep the bottom of the board from touching the side of the case?

Geez, after ye old breadboarding, maybe it is the PSU after all. I don't have any spare stuff around to test or voltage meters, etc. Earlier today I got all the fans and drives to work. Now nothing works. Incredibly frustrating. Everything was fine for two months then it all of a sudden just died. Thankfully, I didn't mail order any of this stuff, otherwise I'd be here till doomsday.

Appreciate the responses.
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a b U Graphics card
a c 716 V Motherboard
September 9, 2010 3:36:26 AM

Cut electrical tape in small squares 1-2 layers over the "standoff's" <or> plastic washers - it will fix any shorting.

Good Luck & Post back your findings!
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September 9, 2010 8:23:08 PM

tape seems to have done the trick - big thanks.

Couple things:

Thing #1 - When I test the PSU, CPU, and fans (no RAM) I'm getting no beeps from the case speaker.
Thing #2 - When I stick the video card on the board, the CPU fan does not spin unless I touch it with my finger. When I remove the video card, the CPU fan spins.

These point to a bad PSU?
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a b U Graphics card
a b V Motherboard
September 9, 2010 8:46:23 PM

Are you sure the case speaker is on correctly? Without any RAM, you should be getting beeps.
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a b U Graphics card
a c 716 V Motherboard
September 9, 2010 8:49:24 PM

Let me explain what I meant from "Hmm, dual rails - do you have a DVM" - if one of the (2) rails is working you get all sorts of Oddball behavior; it means 1/2 of your power might be toast {burnt-out}, and only a Voltage Meter will conclusively confirm this valid assumption. However, the other "good" rail might be okay. Further, the "paperclip" test may easily miss the other rail.

In general, the better PSUs use 1 Rail and utilize Japanese Capacitors (e.g. Corsair). Worst, and this is where people unknowingly make huge budgetary $ errors, is a bad PSU can easily ruin EVERYTHING it is attached to {CPU, GPU, MOBO, etc}. So the $30-$50 savings can be disastrous.

The comment "CPU fan does not spin unless I touch it with my finger..." screams a bad PSU, or if you're really lucky another unknown short.

Footnote: No one can conclusively know what caused your problem, it seems logical a short cascading throughout your system. In addition, if your PSU has become bad or was bad and caused the problem - I would start there. The problems could now be any one component <or> in combination <or> all of: {PSU, MOBO, CPU, GPU, etc}. So its become a guessing game of chance to pick the correct problem(s).
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September 9, 2010 9:14:07 PM

aford10 - yeah, I've double checked. There's a red case light that slowly blinks, which may be the visual complement to the beeps?

jaquith - I understand what you mean by dual rails. I do not have any kind of meter, maybe I'll run out and get one. Boy that would suck if I've got a bad PSU and it screwed up everything. It's a 700W OCZ ModXStream Pro, so it's not top-of-the-line, but it's not junk (allegedly).
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a b U Graphics card
a c 156 V Motherboard
September 9, 2010 9:48:49 PM

Most PSU's under 1000 watts are single rail PSU's even though they may be advertised as multi-rail. A simple way of checking is to measure the resistance between the yellow wires on any power connector to any other connector. A low reading (1 or 2 ohms) means that it is really a single rail design.

Single vs. multiple rails:
http://www.jonnyguru.com/forums/showthread.php?t=3990
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September 9, 2010 11:05:26 PM

Reading more reviews about my PSU, now I wish I never bought it. Now you can find this thing for more than 50% off retail at various places.
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a b U Graphics card
a c 716 V Motherboard
September 9, 2010 11:29:10 PM

^ You're in the majority. I was clueless myself in the day; I built 2 more less identical rigs and burnt out the GPUs on both rigs - WTH?! Then replaced them and 2 months later - a THIRD - WTH? Then both PSUs within 1 month of each other - lovely electrical smell of ooops!

Then I found the VALUE of a good PSU - $30x2 saved $700 lost! Duh me!
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