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Big mistake (help!): which is dead, the motherboard or PSU?

post #1 of 9
Thread Starter 
Motherboard: GA-B75M-D3V
Power Supply: Corsair CX600 V2
Case: Enermax Clipeus ECA3212
CPU: Intel Core i3-3220

I'm helping a remote friend put together a PC. He almost made it, too. When he turned it on the first time, it worked. Normal beep and post.

But then he immediately noticed that the case fan wasn't turning. The case fan has two leads: a 3-pin and a Molex. He had the 3-pin connector attached to a 4-pin MB connector (I don't yet know which pins).

So without turning the power off or listening to what I might say about it, he also plugged in the fan Molex, thinking that both connectors were needed, and the machine immediately shutdown and no longer boots.

The only sign of life is the front-panel LED. There are no LEDs on the MB for diagnostic purposes, unfortunately. No beeps now.

Question: Is there any logical way to determine which is most likely bad given the evidence? He doesn't have a spare power supply handy, and certainly not another board. Does what I described above, and what's excerpted below from the manual, make one more likely than the other? I think someone proficient in electronics would have an idea. Thanks!

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post #2 of 9
Try clearing CMOS if that does not work find a digital voltage meter and do a pin out of the psu 24 pin and 4+4 pin you may have fryed mobo
post #3 of 9
You can check the power supply by using a multimeter to check if the voltage is correct. Follow instructions here: http://pcsupport.about.com/od/toolsofthetrade/ht/power-supply-test-multimeter.htm

If the PSU checks out, the fault is likely in the motherboard.
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post #4 of 9
If it is the fan for the cpu, the computer will not start back up until you plug it back in. Some of the plugs will accept 3 or 4 pin fans. It will not hurt the computer plugging a 3 pin into the 4 slot. The slot and the fan connector will not allow you to plug in improperly without a silly amount of force.
Edited by Nick7269 - 1/12/13 at 9:07pm
     
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post #5 of 9
Thread Starter 
Thanks, I will get him to measure voltages in the morning.

I forgot to mention that he did clear the CMOS: no change.

Edit: The CPU fan was working fine before the incident, so I don't think it's involved. He never had that one on wrong.
Edited by rseiler - 1/12/13 at 9:09pm
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post #6 of 9
Thread Starter 
He picked up a digital multimeter and ran the tests: passes. So, it's the board.

But out of curiosity, why exactly did this happen? Was it more the fact that he hooked up TWO power sources to one fan, or that he hooked up the Molex while the system was on?

I did try to get clarification on how the 3-pin was hooked: he believes it was pins 2-4, which would explain why it didn't work initially (should be on 1-3).

Also, one other tidbit that I didn't know: when he hooked the Molex, the fan did turn on briefly--before the system died.
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CPUMotherboardGraphicsRAM
Intel Core i5-2500k Intel DZ68BC IGP G.Skill Ripjaws 2x4GB 1600 
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Power
Antec EarthWatts Green EA-380D 
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(14 items)
 
  
CPUMotherboardGraphicsRAM
Intel Core i5-2500k Intel DZ68BC IGP G.Skill Ripjaws 2x4GB 1600 
Hard DriveHard DriveOSMonitor
Crucial M4 64GB WD2000EFRX Windows 8 x64 Dell 2007WFP 
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Antec EarthWatts Green EA-380D 
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post #7 of 9
he ran 12v from psu directlly to ground through the mobo cpu fan connector, the psu uses case ground thats why it turned on for a min, look for blown or burnt caps on the mobo, or a small burnt diode.
post #8 of 9
Thread Starter 
Thanks for the explanation.

He reported finding nothing physically out of the ordinary about it though.
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(14 items)
 
  
CPUMotherboardGraphicsRAM
Intel Core i5-2500k Intel DZ68BC IGP G.Skill Ripjaws 2x4GB 1600 
Hard DriveHard DriveOSMonitor
Crucial M4 64GB WD2000EFRX Windows 8 x64 Dell 2007WFP 
Power
Antec EarthWatts Green EA-380D 
  hide details  
Reply
Main system
(14 items)
 
  
CPUMotherboardGraphicsRAM
Intel Core i5-2500k Intel DZ68BC IGP G.Skill Ripjaws 2x4GB 1600 
Hard DriveHard DriveOSMonitor
Crucial M4 64GB WD2000EFRX Windows 8 x64 Dell 2007WFP 
Power
Antec EarthWatts Green EA-380D 
  hide details  
Reply
post #9 of 9
+1 rep for whoever helped
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