PC shorts dead when flashdrive touches case

[amips]

Hi folks!

 

I just built a £1,000 tower for a guy (specs & OS irellevant methinks) and it was OK in my workshop - I used flashdrive to load progs etc.

 

He had it for a few days then rang me up saying it was crashing when he inserted his flashdrive into the front USB port.

 

I went there and put 1 of my 3 flashdrives in and it was OK, so we said his flashdrive must have shorted its PCB. I took my drive out and (luckily) decided to try another, but BEFORE it was actually inserted i.e. just touching the USB slot, the PC instantly powered off-just like pulling the plug!

 

I checked inside especially around the front port for bare wires etc and tried again but it kept shorting. I unplugged the USB header from the mobo but lo and behold it STILL shorted the PC, so I guessed it was an earthing fault. I changed the power input kettle lead for a new one and checked his Belkin Surge protecter was earthing OK but still shorted. I unplugged the power from the Belkin and put it directly into the wall socket but still shorted. So I said I needed to take it back to my workshop for further tests.

 

HERE'S THE STRANGE BIT! :confused: It's perfect in my workshop - I CANNOT make it short.

Anyone out there who knows more about electricity than PCs might be able to help please!

[Dalo Harkin]

Something must be shorting inside the case, Most common are the standoffs that the MOBO sits onto.

 

Also check that none of the PSU wiring is touching the inside of the case as in the Molex pins or something have come loose.

 

It can be one of many things so just check the basics :)

[amips]

Thanks for prompt reply. Can you expand about how the stand-offs could short please?

[Dalo Harkin]

The Motherboard sits ontop of the standoffs giving it direct contact with the case.

All it needs is a screw to be touching a power source (cables under/around the MOBO) and you have current going through the case. When you even slightly touch a metal object to the case (it shuts it off)

 

Loose screws dropped behind the MOBO are also a possiblity so check that

[KenB]

Is this happening with all USB ports or just one particular one ?

[amips]

All ports.

[amips]

I have now returned the PC to the buyer, having taped up all the ends of open cables (molex/sata/floppy/pcie). I guess Dalo may well have been right re the short from one of these cables.

 

I did carry out a "short" test at the clients house and advised him to get rid of a 4-port extension that was plugged into a 6-port Belkin Surge Protector because it lit the tester up.

 

This is going to be one of those problems that we will never be 100% sure about, but my buck goes to Dalo!!!

 

Many thanks y'all.

[Dalo Harkin]

Glad we could help :)