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Posted

We have a new Sony desktop. VGN15S. Very nice it is too. However we get small electric shocks from the metal part of the open CD tray and sometimes (maybe all the time, i dont keep trying it) off a usb port or from the end of a cable attached to it. Obviously non lethal, and presumably low voltage.

It runs off a laptop style transformer brick, with three wires into the brick, although our household's mains electricity is the usual two pin out. Output from the power brick is DC19.5v.

Just before I hurled the machine back at Sony, I tested the machine on my office three wire power earthed supply run directly from the fusebox and there I got no electic shock/leakage. So not a machine problem then?

I can't get my brain around why this is. If the output is DC into the computer, where is the crossover for the live? If the machine needs an earth, how does the earth connect through the transformer as the DC out is only two wires.

I must be missing something - so any ideas?

Posted

It is a common problem in Thailand as they don't earth everything like Farangs do, there have been some detailed posts about this in the past. You could run a wire off the case of the computer to ground as they often do here with washing machines.

Posted (edited)

You are seeing leakage to ground caused by the mains inlet filter, ground your supply properly and the problem will go away (as demonstrated at the office).

You may score by reversing the mains plug in the outlet but it's not the recommended solution.

Inside the PSU the negative rail is connected to the incoming ground which is how the bitey bit is getting to your metalwork. It's actually about half mains so not exactly low voltage, however the current is very small so unlikely to be hazardous.

Edited by Crossy
Posted

i'm working as an IT guy and i can second the solution of the first reply.

this is extremely annoying to get electricity all the time when i touch a computer case, i need to clear the power into the psu and unplug the screen cable to work safely inside the computer as earhting is not present in thailand...

Posted

Same problem here in Vietnam. And whilst the current might not be harmful to people, it did fry my rather expensive sports watch when I plugged it into the USB port. Have since attached a wire to a screw holding the case panels in place and earthed it.

Posted
You are seeing leakage to ground caused by the mains inlet filter, ground your supply properly and the problem will go away (as demonstrated at the office).

You may score by reversing the mains plug in the outlet but it's not the recommended solution.

Inside the PSU the negative rail is connected to the incoming ground which is how the bitey bit is getting to your metalwork. It's actually about half mains so not exactly low voltage, however the current is very small so unlikely to be hazardous.

Thank you Crossy. The clear explanation I was looking for.

I think reversing the outlet helped. I am also running the mains through an UPS. The Sony desk top is really a laptop with a stand and without a hinge. The outer parts are all plastic so no ground access. What really made me start to think is that all laptops will have the same problem, no? And in all two pin outlets (potentially)?

I am not about to go jamming my fingers onto the metal parts of CD drives to find out but I think I will go off to buy a voltmeter.

As to earthing in the home. I had an electrician come and run a line from the board to my office to run all my equipment. Absolutely no-one understood why I was making such a fuss. Including the electrician which is disturbing.

Also the only metal earth I can find was this lovely large cable running down the outside of the building straight into the groud......Dont worry, I realized!

Posted

If unable to find a suitable "earth" ground, an "isolation" transformer (electrically separate windings) should do the trick. "Autoformers" with shared windings are the culprit .. cheaper to build, smaller in size.

For it to work correctly, ALL components must plug in to the isolated side of the transformer.

Posted
What really made me start to think is that all laptops will have the same problem, no? And in all two pin outlets (potentially)?

My old Dell (3 pin cable) would bite hard if run from an ungrounded outlet. My new HCL (2 pin cable) has no such issues.

The answer I always use is "if it has a 3 pin plug then it is expecting a ground".

You don't need a very good ground to remove the tickle it has a large source impedence.

Posted
You are seeing leakage to ground caused by the mains inlet filter, ground your supply properly and the problem will go away (as demonstrated at the office).

You may score by reversing the mains plug in the outlet but it's not the recommended solution.

Inside the PSU the negative rail is connected to the incoming ground which is how the bitey bit is getting to your metalwork. It's actually about half mains so not exactly low voltage, however the current is very small so unlikely to be hazardous.

Thank you Crossy. The clear explanation I was looking for.

I think reversing the outlet helped. I am also running the mains through an UPS. The Sony desk top is really a laptop with a stand and without a hinge. The outer parts are all plastic so no ground access. What really made me start to think is that all laptops will have the same problem, no? And in all two pin outlets (potentially)?

I am not about to go jamming my fingers onto the metal parts of CD drives to find out but I think I will go off to buy a voltmeter.

As to earthing in the home. I had an electrician come and run a line from the board to my office to run all my equipment. Absolutely no-one understood why I was making such a fuss. Including the electrician which is disturbing.

Also the only metal earth I can find was this lovely large cable running down the outside of the building straight into the groud......Dont worry, I realized!

You could screw a wire onto the external monitor socket, just need to find the right screw or wreck an old serial cable or similar.

Posted (edited)
You could screw a wire onto the external monitor socket, just need to find the right screw or wreck an old serial cable or similar.

I have run an insulated wire from a known earth feed and put it behind one of the screws that fasten the comp. casing.....................don,t know if this could cause a problem but it got rid of the minor kick i used to get before hand.

Especially when my hands where sweaty.

The fix i did some 3 years ago with no apparent after effects ????

marshbags :o

Edited by marshbags
Posted

This can ruin your computer if by chance you touch one of the data connections or line-in from the sound card. Then there will be a couple of hundred volts to absorb by the circuits. If you cannot find a real earth it helps to connect the computer to a metal frame of the window or something similar.

Posted
This can ruin your computer if by chance you touch one of the data connections or line-in from the sound card. Then there will be a couple of hundred volts to absorb by the circuits. If you cannot find a real earth it helps to connect the computer to a metal frame of the window or something similar.

How about that you would get free burglar protection by making the window hot as well.

Posted

.

How about that you would get free burglar protection by making the window hot as well.

Nope, it is only a very weak current which leaks away easily from the frame via the stone walls to earth.

Posted (edited)
This can ruin your computer if by chance you touch one of the data connections or line-in from the sound card. Then there will be a couple of hundred volts to absorb by the circuits. If you cannot find a real earth it helps to connect the computer to a metal frame of the window or something similar.

Thanks for highlighting that Obiwan

It is always disconnected before taking the casing cover off and exposing / physically touching data ect.

The case cannot be moved until it is disconnected as i,ve purposely left the feed short, justin case a technition ??? pays maint. visit while i,m out.

It is always advisable in any case not to touch bare / exposed data connections ect. under any circumstances, IMHO without safeguard protections against contamination.

marshbags :o

Edited by marshbags

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