New Build - USB sparks and turns on PC

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Franco Constantin

Honorable
Dec 27, 2012
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10,510
Hi,

I recently built a new pc. I was plugging in a USB to the back of the case and there was an electrical spark and the PC started by itself. I'd like to know what the issue is there. I've also done this with a mini dp plug – blue sparks + start up pc.
It occurs on the front usb ports and the back usb ports. The usb must be powered. Rubbing the usb on the backplate alone will get it starting up as well.

Whilst it's on i tried the same test – it doesn't turn it off.

The PC runs fine otherwise.

Thanks for any help.
 
Solution
manofchalk
Well, never heard of this problem before :lol:.

Sounds to me like your power button connectors are making contact with the case, so whenever something makes contact with the case it shorts out and therefore starts the machine.
Try it with a screwdriver or other metal object but hold it by something non-conductive. If it doesnt turn on, you can be sure that its a short.

Disconnecting your case's power and reset button will likely solve the problem, though then you have to find a way to easily turn the machine on and off.
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manofchalk

manofchalk

Glorious
May 11, 2012
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Well, never heard of this problem before :lol:.

Sounds to me like your power button connectors are making contact with the case, so whenever something makes contact with the case it shorts out and therefore starts the machine.
Try it with a screwdriver or other metal object but hold it by something non-conductive. If it doesnt turn on, you can be sure that its a short.

Disconnecting your case's power and reset button will likely solve the problem, though then you have to find a way to easily turn the machine on and off.
 
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Solution
spat55

spat55

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Jun 4, 2012
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This, I wouldn't know what to say but this does make sense.
 
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quilciri

quilciri

Splendid
Mar 16, 2012
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23,965
If you want to dig further, you can trace the wire from the power button to the jumper to find where it is exposed and touching the case (the most likely point of contact would be just behind the power button itself. Then you can either wrap electrical tape around the exposed wire, or you can melt abs plastic around it (will require a soldering iron; replaceable tips better but not required. You can get a cheap iron for $20 at radio shack, and ABS plastic for ~$10 at hobby stores....possibly at the radio shack as well...you'll want an open window and small fan for the ABS fumes)

alternately, you could remove the mobo, pop out the I/O panel and paint the edges of the case where the panel goes in, which in theory would prevent anything you plug in the back from completing the circuit.

good luck!
 
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Major_Trouble

Major_Trouble

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Jun 25, 2007
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Your diagnosis sound good. If your correct it would be better to sort out the power/reset button connectors short than just disconnect them.
 
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Franco Constantin

Honorable
Dec 27, 2012
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10,510
I've just started testing. I unplugged the pc and checked for any stray cables. I replugged and tried starting it with the powered usb - nothing. i started up normally then shut down normally. tested again and it happened. Does that mean anything?
 
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Franco Constantin

Honorable
Dec 27, 2012
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10,510


So using a screwdriver does nothing. Whatever I touch it with must be powered. ftp://66.226.78.21/manual/Z87%20Pro4.pdf - if you check page 23 can you explain which ones I should unplug.

Edit: So i disconnected "pwrbtn" (row 1 - pins 3 and 4) and "reset" (row 2 - pin 3 and 4). I then tested again and the pc started against whilst those cables were disconnected.

If you look at page 23 - I have the top row connected. the next row - pins 1 (hdled+) ,2 (hdled+) and 5 (ground) have no connection and are exposed.
 
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manofchalk

manofchalk

Glorious
May 11, 2012
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48,960
Hmm... So its not the case button then if it still happens while their disconnected.
The fact it only works with powered devices is also a intriguing.

Maybe the back of the motherboard (particularly, your power button positive connection) is making contact to the case and when you touch it with a powered device it sends acts as a power on signal.
Why it doesn't just go directly to Ground through the PSU I have no idea.
Have you used motherboard standoff screws?
 
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Franco Constantin

Honorable
Dec 27, 2012
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I have. I don't want to check again but I'm guessing I'll have to.

This is a dumb question - but the bottom right pin is not supposed to be connected to anything?

http://imgur.com/a/vwLyE - My PC
 
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Franco Constantin

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Dec 27, 2012
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10,510


I'm not using it.

The cable for "pwrbtn" and "reset" are two cables with one interface. One cable is red and the other black (i.e. pwrbtn and ground + reset and ground). How do I know which is for ground? I currently have the red cable on the right for both but looking at page 23 - ground is on the left for "reset" but on the right for "pwrbtn". I am not using the 5th pin on the bottom row - also labelled "ground".
 
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