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Built computer won't start with motherboard installed in case.

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February 3, 2012 5:26:43 PM

Hello,
I just finished building my second computer yesterday and after checking to make sure everything looked right I pressed the power switch to start it. The system started to turn on but immediately blinked off after about a quarter-second. After unplugging everything I checked to see if all the components were secure and nothing extraneous was contacting the mobo, then I attempted to start it again with the exact same results. After searching this site for possible solutions, I found a list of things to check and went through them one by one. With no solution found, I disassembled the components, pulled the mobo out and reassembled it outside the case. When I completed the power up circuit the system started perfectly. I confirmed that the case standoffs are in the right positions and only have as many as are mounting holes in the mobo. I reinstalled everything and attempted to start with the exact same results as before, no powerup. Anyone have any ideas on what I may have missed?
a c 238 V Motherboard
February 3, 2012 6:13:48 PM

A good start on problem determination.


My suspicion at this point is that there is a short in the case front panel wiring, or the front panel connectors are miswired or mislabeled.

Disconnect those wires, and try to start the motherboard in the case with the motherboard pwr button if you have one, or with a screwdriver if not.
Then, attach the front panel connectors one, by one, and retry.

Double check that the front panel wires are connected to the proper pins.
If, for example you connected a hdd or pwr led cable to the reset pins, you would get similar symptoms.
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February 3, 2012 6:43:34 PM

geofelt said:
A good start on problem determination.


My suspicion at this point is that there is a short in the case front panel wiring, or the front panel connectors are miswired or mislabeled.

Disconnect those wires, and try to start the motherboard in the case with the motherboard pwr button if you have one, or with a screwdriver if not.
Then, attach the front panel connectors one, by one, and retry.

Double check that the front panel wires are connected to the proper pins.
If, for example you connected a hdd or pwr led cable to the reset pins, you would get similar symptoms.


I actually did consider this, just forgot to add that I had tried it. With everything installed in the case I removed all the front panel connectors and attempted the startup manually with the same result, a millisecond of power then nothing.
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February 3, 2012 6:51:03 PM

I'm wondering if maybe one or more of the mounting screws are somehow short-circuiting the board.
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a c 238 V Motherboard
February 3, 2012 6:58:37 PM

hwhite1725 said:
I actually did consider this, just forgot to add that I had tried it. With everything installed in the case I removed all the front panel connectors and attempted the startup manually with the same result, a millisecond of power then nothing.


Strange...

The good news is that you know your parts are good.


Did you use the proper screws for the standoffs? If they had heads that were too large, you can cause shorts with the motherboard.
I have heard of this problem before. Check to see if the heads might be touching something they shouldn't. It could be an extra piece of solder left when the motherboard was built.

You could try insulated washers if that were the situation. Leave at least one connection so that the case is grounded to the motherboard. The psu will take care of motherboard grounding.

I think there has to be a short somewhere.

Can you put parts back into the case, one by one, and see which part the failure starts.

Start with the motherboard by itself.
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February 3, 2012 7:18:33 PM

I actually did notice that there appears to be sloppy soldering around the mounting holes. I will check that first and if that still doesn't work then I will try installing one part at a time and testing.
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a c 238 V Motherboard
February 3, 2012 7:22:58 PM

You might try using only two mounting screws in what looks like the cleanest holes. If that works, then insert the rest, one at a time.

Is it possible that the short is coming from the i/o plate? You could try without that.
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February 3, 2012 11:16:04 PM

Ok, I tried all the possible solutions in this thread so far, none have worked. I even lined up the mobo with no mounting screws and no i/o plate and nothing installed and it still wouldn't start up. Still starts fine out of the case. I am officially out of ideas.
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a c 238 V Motherboard
February 4, 2012 12:27:24 AM

You got me too.

It has to be something simple.

Whar case, motherboard, and other parts are we talking about?

Post a pic of the motherboard out of the case, when it works, and one in the case when it does not.

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February 4, 2012 11:38:49 AM

Ok, here is the setup:

- AMD FX-6100 Zambezi 3.3GHz Socket AM3+ 95W Six-Core Desktop Processor FD6100WMGUSBX

- GIGABYTE GA-990XA-UD3 AM3+ AMD 990X SATA 6Gb/s USB 3.0 ATX AMD Motherboard

- CORSAIR Vengeance 16GB (4 x 4GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model CMZ16GX3M4A1600C9

- XFX HD-687A-ZHFC Radeon HD 6870 1GB 256-bit GDDR5 PCI Express 2.1 x16 HDCP Ready CrossFireX Support Video Card

- XCLIO Windtunnel Fully Black Finish 1.0 mm SECC Chassis ATX Full Tower Computer Case

- Corsair- Gaming Series 700-Watt ATX CPU Power Supply

Plus of course various SATA HDD/optical drives. I will take some pictures tonight when I get home from work. I'm also going to remove the mobo and install the standoffs and mounting screws outside the case to see if it will start.
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February 5, 2012 9:10:18 AM

it has to be the standoffs maby you should try different standoffs (if you have any) or even if you can try the parts in an old (different case)
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February 5, 2012 9:11:30 AM

i also had the exact same problem i fixed it by replacing the psu (obviously not the problem in your case)
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