I turned my PC off today before dinner, and it was working fine. I came back afterwards, turned it on and I heard a crack, with a smell of frying electrics. The PC rebooted (as it does when it shorts out. I know from when I decided to start wiring up my case lights with the PC on It doesn't seem to do any damage though, it's happened a good few times before), and my fans stopped working.

The fans are coming through a 5.25" controller, which has a LCD display showing temps and fan speeds. The display (which uses 5v) is still working, but the fans and the LEDs inside the controller (which use 12v) aren't. When it rebooted the first time, I opened up the side with the ghetto wiring, and tapped it a few times. The fans started cutting in and out intermittently then. I figured it was a loose connection, so I re-did all of the joins and connections, and tried again. Still no luck.

All of the hard drives and disk drives are receiving full power, and the multimeter is showing 5v and 12v as expected on molex. The machine refuses to boot either, it stops right before it checks the disk drives for boot disks. It goes through its routine checks, and gives its usual list of hardware and controllers, which are all present. It stops on verifying DMI pool, which usually only takes a few milliseconds. Going into BIOS, it shows all voltages reading fine, and detects the HDDs and disk drives.

When I connect just the 12v molex wire straight onto one of the LEDs in the fan controller, it lights, even if I remove the molex plug feeding it. I'm fairly sure this means the negative is earthing against the case somewhere, as all lights work when just a positive is connected. I've tried the obvious solution of unplugging the molex plugs going to the case lights and fan controller (the only things I wired myself), but it still refuses to boot and earths somewhere. The weird thing is the fans still won't come on even if they're connected to the controller, which to me sounds like one of the negatives going to the controller is earthing along the way. I've traced it along and there's no signs of damage though.

I'm not sure if it's just the weather, but the PSU fan stays on about a minute after the machine is shut down, which it never does. Maybe it's the PSU itself earthing against the case, causing it to heat up, I'm not sure. The PSU is warm to touch on the outside, which is fairly usual.

I do have a spare 350W PSU floating about, but I'm not sure if it will be able to replace my 550W. I also don't want to have to find and remove all of the PSU's wiring, which is lost throughout the case at this stage after various lighting projects. I'm sure these aren't the problem though, I've removed them all to test it. I'm absolutley stumped at this, it was working flawlessly all day at TF2, and I shut it down and started it as normal. Hopefully I've missed something obvious, or someone smarter than me will see what I've cocked up on

Cheers



EDIT: I've solved the non-booting issue. I left my memory stick in which was formatted as NTFS when I updated Windows 7 from it, and it was trying and failing to find a boot disk on it :doh: (like I said, something REALLY obvious...) So at least I can short out the fans and play away for the mean time And the PSU is acting normal, and not causing the boot failure. So it probably is just a negative earthing somewhere, or else the fan controller is toast...

EDIT2: After a bit of poking around, I found one of my fan controller wiring jobbies (held together with insulating tape has come loose...Problem solved, and I feel like a tool after trying to find a problem for the last 2 hours

EDIT3: Actually, it's still earthing somewhere. The controller still works without a negative molex attached. But I don't care, it's working again

"earthing" - is that the word used in the UK? We call it "grounding".

Yes. AFAIK it comes from the days of the BL cars. My Mini has a sticker saying "body wired negative earth", as they all do since 1959. I presume that the car manufacturers back then decided that would be the term we'd use Maybe grounding is the official electrician term, but earthing is what I'm used to

It's all fixed and put back together now, working great again. Since it is earthing, it was probably just a positive came into contact with the case, maybe it got sucked into a fan or something and came out of the insulating tape

If something like that happend to me, I'd tear the whole computer apart and rebuild it making sure all connections are tight and secure and no wires are damaged.

I would suggest doing that now, to make sure you have no ground faults.

By tear it apart I mean lie the case on its side, remove all power connections, remove IDE and SATA cables, hang all of the wire looms for power out the side or top of the case since it is on it's side.

Check all cables for damage and check the braided shields, if you have them, for damage. If everything looks good, begin to put it back together carefully and find ways to manage all the cables so thay don't rest against anything sharp.

If you have any home made power connections for things like fans or lights, I would consider using heat shrink or electrical tape to cover them.

If you suspect there is a grounding problem I would not run the computer if I where you.

There is a lot of home-made connections, all of the fans and case lights were done by me. The majority are soldered and heatshrink'd, some are just twisted, wrapped in insulating tape and cable tie'd. All of the cables are neatly put around one side of the motherboard (without actually being behind it...my case has a gap between the motherboard's tray and the side of the case), away from the fans and the front of the motherboard. The only cables that could come into contact with the fans are the alarm-cable type ones which run under the fans to the lights. If these got a strong enough pull (like being sucked into a fan), they could easily pull off the insulating tape. I've visually inspected all exposed wiring, and it seems fine. There's no joins near the outside of the case anyway.

If the case is grounding, which I assume it is (unless the controller is using something else for earth, it also has USB, eSATA, firewire and a memory card reader), it's been like that since I built it. This is the first time something like this has happened in almost a year of having the machine, so I'm not too worried. It was never right from day 1 though, it used to reboot itself immediately after being shutdown, regardless of BIOS settings or OS used. That righted itself a few months ago however.

Thanks for the help though, much appreciated. I kinda freaked earlier when it happened, there was smoke and a burning smell everywhere when it happened and I shat brix

E: On second thoughts, I have a good idea why it's grounding. I made the lights by putting 3 LEDs together (twisting the legs of each in series) and soldering on a resistor and earth on one end and positive on the other. It's entirely possible that one of the negatives is touching the case, as they're all taped onto it. Tomorrow I'll redo each, and see does that sort it. That's the only thing it could be unless it's the PSU itself earthing

...The only thing you should be worried about is a partial connection(as the chances of a dodgy intermittant connection are near nil if you've twisted the ends of the wires round one and other). A partial connection will obviously get hot and pull extra load from the PSU not to mention the heat transferred around the board and to nearby components, and if your a real cowboy you could set fire to a CD or something.

If you think any of the connections are a bit iffy get a multi-tester and test each end of the cables in quistion in the miliohm's setting on the tester, a higer resistance than the unbroken piece of the cable will tell you straight away if the connection is not 100% and will fail under load.

Lol, "earthing."