Power coming from somewhere

[pmonett]

Something unexpected cropped up a few minutes ago. I have just upgraded my sound card from an Audigy 2 to an X-Fi Gamer.

In order to take out the Audigy 2, I obviously unplugged the PC from the mains, and watched the LED on the motherboard go dark before touching the card. While taking the card out, I felt a bit of tingling where my fingers touched the case, but other than that, nothing out of the ordinary.

I know my case has a few rough edges, so I don't pay to much attention to the brushing-raw-skin-against-a-razor feeling that I get whenever I do get my fingers near it.

Then I proceeded to insert the X-Fi card into the case, and that's when I got a shock. Literally. It was impossible for me to touch any metal parts on the card as soon as I had connected the audio jack for the DVD drive.

Now, I insist that the mains have been unplugged, and the motherboard indicator went dark before I touched any hardware components.

What was connected at the time was the screen connector, the keyboard and mouse leads, and the USB extension cable I have handy to avoid bending myself in two every time I need to plug in my phone.

The PSU is a ZEUS 800W unit, but hey, if the motherboard LED is dark, there isn't supposed to be any current flowing, right ?

800W is a lot. I have no electrical knowledge, so I'm going out on a limb here (I read way too much sci-fi anyway) but could there be some sort of energy transfer from this PSU to the card via, I don't know, magnetic influence or something ?

More realistically, could the screen cable, connected to a powered-on-but-in-sleep-mode screen be the culprit ? Can power go from the mains, to the screen, through the cable to the casing ?

Seems to me that would be a major recipe for a short, no ? Shouldn't something blow a fuse ? Or burn out ?

Could someone please explain ?

Thanks.

Pascal.


I've got nothing to hide, and I'd very much like to keep that away from prying eyes.

 

[G0AOZ]

You seem to be indicating that the strength of shock you received was much worse when the new card was being plugged into the motherboard than it was after you'd initially removed the old card. Can you rule out static discharge?

First thing to do is switch off the monitor and any other peripherals (printer etc), and remove the power plugs from the mains sockets.

Have you, or anyone else in the premises recently experienced electrical shocks from equipment in use? If yes, then immediately isolate that equipment as well. You may have a mains-borne problem which should be immediately checked out by the power company or a qualified electrician.

Getting back to the computer... If you had switched off the computer in the normal manner, and then removed its mains plug, I do not believe there is any way your 800W PSU could be part of the problem. Power to the motherboard is provided at low voltage levels, 3.3v, 5v and 12v etc. Anything wrong inside the PSU that had allowed either AC or high voltage DC to be connected into these low voltage rails would have immediately resulted in the various motherboard and PSU protection circuits shutting your PC down. You have mentioned no such problems whilst it was running...

If mains circuits in your premises are ok, then I would suggest that there is possibly some sort of current leakage or fault in the monitor's PSU, which is putting a voltage on the signal connections back into your video card and onto the motherboard.

If you are sure that you can rule out mains wiring problems within the premises, then you could possibly check for stray voltages/potential differences between equipments, if you had a suitable voltmeter. However, I am reluctant to tell you to do this without having firsthand knowledge of your situation and capabilities.

Take advice from a local qualified electrician if you have the slightest doubts about anything electrical...

ROGER - G0AOZ.

 

[pmonett]

Thanks for your prompt reply.

To be a little bit more precise : when I say shock, I do not mean the lightning-arc type accompanied by an audible sound.

It is more the kind where you touch a wire and let go suddenly thinking "IT'S LIVE".

I rather prefer the monitor causing the issue. Seems plausible, though unpleasant. I'll have to try unplugging the monitor cable and then the PC, then touching a wire again to see what gives.

Cheers,

Pascal.


I've got nothing to hide, and I'd very much like to keep that away from prying eyes.

 

[G0AOZ]

CAUTION! "It is more the kind where you touch a wire and let go suddenly thinking "IT'S LIVE".". You should be very careful about re-touching the card or the PC with this fault condition still prevalent.

From what you've told us so far, it would appear to be leakage from the monitor onto the video signal cable. My guess would be that you were touching the computer case with one hand and the card with the other. The current leak was going from the card through your body to the case which had a return earth path to the monitor. However, without tests using a voltmeter, it is difficult to determine if there is a fault on the earthing system, i.e. faulty monitor, with an earth path going from the card to ground via your body and legs.

Are your premises equipped with a Residual Current Circuit Breaker (RCCB)? This ought to give protection where mains voltages are leaking, but you shouldn't rely on a device like this to save your skin.

If you are in any doubt, please get your wiring installation and computer equipment checked by a qualified electrician.

I was going to say electricity is shocking stuff, but this IS a serious matter...


ROGER - G0AOZ.

 

[pmonett]

My PC is connected to the mains via a UPS controller - which happens to be of the VA800 category.

I would suppose that, if the house did have a mains leakage issue, the UPS would catch that and deal with it.

In any case, the next time I deal in hardware, I will unplug EVERYTHING from the case, just to make sure.

Cheers,

Pascal.


I've got nothing to hide, and I'd very much like to keep that away from prying eyes.

 

[cbs604]

Not sure I understand your scenario here. When you say "screen connector" I assume you mean the video cable to the monitor. Surely then, this was unplugged while you pulled the old card and installed the new one.

You say you got a shock when inserting the new card, but could not touch the card after plugging in the DVD audio cable. What came first?

Have you unplugged the monitor power cable to isolate a possible source of the voltage?

Cheers,
Brodie

 

[G0AOZ]

cbs604, the poster was changing the SOUND card, not the video card. Data (video)lead from PC to monitor remained in place whilst the chaneover took place, hence my posts above.

pmonett, you're now giving us new information re the UPS! Please consider the following points:-

1. Did you switch off the UPS so that it was giving no mains output during the time you were changing cards?

2. Did you switch off the mains supply going into the UPS?

3. Did you still have power leads plugged in between PC and UPS and mains socket? This will tell us (assuming no faulty earth connections) if there was a path to earth between the PC and the mains socket.

4. Is the monitor plugged into a different mains socket/circuit, to that of the PC/UPS.

5. What else is plugged into the UPS?


ROGER - G0AOZ.

 

[stduc]

Does the PC still work?

More realistically, could the screen cable, connected to a powered-on-but-in-sleep-mode screen be the culprit ? Can power go from the mains, to the screen, through the cable to the casing ?

Yes, this is possible, if, for example, the earth and neutral or live and neutral have been interchanged anywhere in your circuit. This could be in a plug, socket or at the fuse box.

You can check with something like this

http://www.campervanstuff.com/shop_stuff/index.php?mod=product&id_prd=1000

or get a qualified electrician in.

To be sure, when working on electrical equipment, always unplug it from the mains and anything it is attached to that may have power. Switching off is not sufficient. You should then ensure that it is earthed to leak any static and that you wear an earth strap to ensure you carry no static.

[navy]When I married "Miss Right" I didn't realise her first name was 'always'. LOL[/navy]

 

[pmonett]

All my PC equipment is plugged via extension blocks to the UPS. That includes the screen, the sound speakers, router/firewall, and the PC itself.

It took a shortcut when I said I had unplugged the PC from the mains - I actually unplugged the power cord from the PSU. Given that, it doesn't matter much what was the other end, right ?

I do believe it is the screen that is the culprit. Last night I disconnected the video cable from the PC and touched the pins on the cable end. On one or two pins, I felt current. Seems a bit counter-productive to send current from the screen to the PC, but I guess that has to do with the PC detecting whether or not a screen is connected.

Anyway, the hardware works fine, thank you. And, as I said above, I now know that ABSOLUTELY EVERYTHING must be unplugged from the PC case in order to be sure no current has a chance to get anywhere.

Thanks for your replies !

Pascal.


I've got nothing to hide, and I'd very much like to keep that away from prying eyes.

 

[G0AOZ]

Glad to hear that everything is working ok. The fact that you can physically detect voltage on the video signal cable indicates there is a fault somewhere. Bear this in mind if you experience other problems in the future...

ROGER - G0AOZ.