-72v on video case

[Mark25]

Hi,
My Ferguson Videostar FV32L has –72v on the case w.r.t. earth, (I wondered why I kept getting small shocks of the bare metal corners!) has anybody else had a similar experience before i start “wading in”, so to speak. It works fine. Any advice appreciated, as i don't feel happy floating my DIY, or bought! hi-fi up to this level!
Thanks in advance.
Mark

[jean-paul]

Hello Mark, is this device meant to be used earthed ? If so, are you using an unearthed power cord or switchbox ?

Some devices that are meant to be used earthed have capacitors for taking out RF garbage from neutral and phase ( in the Netherlands brown and blue wire ) to earth. The case is than connected to the earth pin of the Euro connector. If you use it unearthed the caps are some kind of voltage divider and the case will have a voltage on it. Most of the time it is half of the 230 V i.e. around 115 V.

Strange thing is you mention a negative voltage. Did you measure AC as well ?

Jean-Paul

[dhaen]

This is most probably just leakage, or static build up.
Connect an ammeter. I bet you won't find more than a few micro-amps.
If I'm right, there should be no harm in earthing the case to overcome the problem.

Cheers,

[jean-paul]

Leakage or static buildup are sometimes enough for damaging valuable electronics that are connected to the device.Even when the current is in the microAmpere range.

Also the tickling feeling when using the device isn't exactly a pleasure. I would only advise earthing if the device is meant to be used earthed. In fact it should be used earthed then.

Otherwise I would suspect it and call the service center of that particular brand and ask them for advise/ information.
If the voltage is really DC 74 V it is also against European safety regulations.

This site has some info on what is normal and what isn't: http://www.elektuur.nl/o4s/index.html

Please check "Zelfbouw en veiligheid" for some understanding of safety regulations.

[dhaen]

I wouldn't be surprised if it wasn't the VCR, but the TV it is connected to. The allowable non-fault leakage via the aerial socket is "feelable".
In most installations, the VCR will find a medium resistance path to ground through the connected aerial (antenna) feeder.

[jean-paul]

Good point John ! I wasn't thinking of the device connected to a TV set. First thing to rule out some problems is to measure the unit stand-alone. Still wonder about the fact it is DC and not AC.

[dhaen]

DC might be static I suppose. Hence my comment about measuring the current.
If not, the only place the VCR uses a negative voltage is the vacuum florescent display.

Jean-Paul: Your comment about not earthing some chassis is correct. But the VCR will have a chassis that is virtually earth, and becomes earth whenver a piece of earthed equipment is connected.

[Mark25]

All,
Thanks for the prompt replies.

Jean-paul I don’t speak Dutch, I am English, I just live in Heerenveen for a laugh! so I cannot read the useful info you sent.

The -72vdc was the video alone. I should mention the video is a UK model and I am using it in the Netherlands but I did have the problem in the UK as well. I have done some more measurements. The case is at –72v dc all the time and 113 vac or 120vac depending on what direction the 2 pins mains plug is in the wall.

The unit is not intended to have an earth, the case is directly connected to the pcb 0v’s in a few places. I thought about switching the dvm to the 10A range and checking the current yesterday. But if there is a fault, it will destroy a previously working machine. Also, from previous experience, if the charge is static related the dvm tends to load it enough for it to gradually disappear. This does not happen in this instance, the 72v is solid.

Anyway, Happy newyear/oud jaar avond (NL) to all
Mark

[pinkmouse]

Hi Mark

Best leave well alone and take it back for repair, methinks

Happy New Year all

[AudioFreak]

Mark25,

I have to tell you your VCR with -72vdc and 113vac on the metal case is a very serious health hazard and we strongly recomend you have it repaired by a suitably qualified person.