Just put together a new system, its supposed to run 4 HDTV's for a restaurant. I got everything up and running on a single monitor then went to test dual monitors to make sure the second graphics card was working right... ZZZZZT! Sparks flew. The DVI cable from the monitor was throwing sparks if it came in contact with ANY spot on the case. We're talking welding style sparks, as in part of the shield around the DVI pins is GONE.
This doesn't happen if the power supply cable is unplugged. I popped the case to make sure no molex connectors are touching case anywhere or no wires pinched or anything; and sure enough, nothing seems amiss. I suspected it wasn't an issue with the case. As both monitors are ACER p201's, bought at the same time. The one I normally use plugs in fine, no problems. My wife's is the one that sparks. So i tried (hesitantly) the VGA cable from her monitor. Same result. What the heck????? I'm guessing theres pos voltage to the casing on my wife's monitor?
Here's system details.
ACER p201 monitors, bought Reconditioned
NZXT Rogue cube case
HEC Orion 585w PSU
Jetway MA3-79gdg Combo Mobo
AMD Phenom2 x3 710 2.6 Ghz
Two Powercolor ATI HD3650's
WD 80gb SATA drive
some samsung DVD/CD-rom IDE drive
I was concerned that was the case late last night and I pulled the mobo off the tray and remounted with thin plastic wafer washers on back and front of the mobo to isolate the screws and I'm still getting stray voltage. Only with that particular monitor though. I've even tried another monitor from another computer. No issues with that one. I'm beginning to think somethings seriously wrong with her monitor. Her case is painted and clearcoated, same with all the pci slot covers and card face/backing plates... so i think thats why we never noticed it, theres no metal/metal contact from graphics card backing plate to case.
This doesn't happen if the power supply cable is unplugged
Should have specified, monitor power supply cable. If actual PSU cable on pc is unplugged but unit is grounded, say against my worktable, still get sparks.
Do you have the monitors and computer all plugged into the same electrical circuit (i.e. the same outlet)? Do you have properly wired 3-prong plugs in your house/apartment? Having lived in old buildings with 2 prong plugs and with incorrectly wired 3-prong plugs, I can tell you this is a possibilty (and a scary one, since you could also get a nasty shock as a result).
No guarantees, but if you have connected to two different circuits/outlets, and one outlet is wired incorrectly, i.e. hot/neutral or (heaven forbid) hot/ground reversed, this could be the cause, as one monitor's case could be floating at high voltage, and the computer (or the other monitor) could be providing a path to ground, yielding a high current path through the shield of your video cable, which would cause exactly the problem you are talking about. Also, the ground conductor in a tv coaxial cable can sometimes be the source of problems like this, though I've never heard of problems this bad.
Simple test: Try disconnecting all other components and TV cable from the HDTVs. Then try plugging the computer and both monitors into the same power strip.
If plugging into a single power strip solves the problem, get one of those 3-light outlet testers from a hardware store and check your outlets. Same deal if the problem goes away when disconnecting the TV cable. (This sounds like a ground loop problem, common in mixed component AV setups, but in your case, it's magnified to a dangerous level).
If the problem does not go away when all devices are plugged into the same power strip, (with the TV Cable and all other devices are disconnected), then the problem is definitely with the computer or monitors. Get a cheap multimeter from a hardware store or harbor freight or wherever, and check to see how much voltage there is between the DVI cable's shield and the case of the computer where you've been finding the sparks. Check both for AC and DC voltage -- DC voltage points to a power supply problem, AC points to a wiring problem in the building.
BE CAREFUL -- if this is happening due to high voltage (120 v, or anything above 30v or so), you could be shocked/electrocuted by touching the computer case with one hand and touching the DVI cable's shield (or the TV cable's shield) with your other hand. Rubber kitchen gloves (dry, and with no holes) are an easy way to reduce this risk when testing -- they are not really rated for high voltage, but they are certainly less conductive than your bare skin. Have another person around when you're doing this testing, armed with a wooden broomstick (or something else non-conductive) to knock wires out of your hand, in case electric shock should cause you to clench your hands and not be able to let go.