Voltage from Sky+ Scart Cable

[ChuckMountain]

Just hooking the old TV up after returning a new faulty LCD one I was hooking the Sky+ box (Pace Version 2) and I got a minor voltage tingle of the scart lead when I touched the ground connector.

I thought this was a bit odd and managed to get a voltage everytime I made a circuit between the ground connector and any other ground. I wouldn't have thought this would have happened so I got my multimeter out and measured the voltage at ~70V which has got me slightly worried. The current was measuring only a few mA. 70V is a bit high I would have thought for internal components which normally work at 5 - 12 V.

Has anybody experienced a similar problem or know what is causing it. The TV appears to work fine though, although the LCD did go back because it got interference on the Scart inputs (concidence?) The DVD does not do the same if you plug the same lead in.

Of course its not under warranty and I have upgraded the disc but I can't think of why it would do this. Or is it normal?

[JayCee]

Originally Posted by ChuckMountain

I thought this was a bit odd and managed to get a voltage everytime I made a circuit between the ground connector and any other ground. Or is it normal?

It is normal and nothing to get worried about.
This is simply a "potential difference" between two different "grounds" and will have nothing to do with your previous LCD set scart fault.

[GaryB]

This is normal on any double insulated appliance and is caused by very slight leakage through the capacitors that are present to ensure EMC (Electromagnetic Compatibility) compliance. As you've noticed, the current is tiny and is only usually measurable with a high impedance meter.

I work for a manufacturer and we get regular calls about it.

[SamRadford]

It's quite normal and it's caused by the fact that you touched connections without unplugging the equipment first. Despite what people might think, Scart leads (and LNB cables, Phono etc.) should not be touched while the equipment (all equipment) is still connected to the 230v supply.

[ChuckMountain]

Originally Posted by SamRadford

It's quite normal and it's caused by the fact that you touched connections without unplugging the equipment first. Despite what people might think, Scart leads (and LNB cables, Phono etc.) should not be touched while the equipment (all equipment) is still connected to the 230v supply.

I agree with you in part. The safest way to connect equipment is always with the power off, even then your capacitors will still be charged and there is a risk of shock. Would the particular capacitors in question still be charged for a duration of time after?

The wire in cables such as Scart and phono are designed to only carry low voltages/current and ideally shouldn't be carrying a voltage they aren't designed to. A manufacturer would be in serious trouble if his scarts were carrying 230V.(might be too late for the poor sod that found out the hard way but they would get sued)

The scart cable in question has metal connectors so I can't help but touch the scart ground when plugging it in. If my caps where still charged I would still be in the same boat.

[SamRadford]

You are missing the point. The leads are connecting the equipment chassis together, maintaining zero potential - assuming there's at least one ground somewhere in the system. Even if there isn't, at least they are at equipotential.

But when you have a lead disconnected and the equipment still powered, that 70 volt "tingle" could easily get applied to a sensitive input by your delicate fingers and do irrevocable damage.

I'm not considering your safety but the safety of the electronics.

[Nick_UK]

It's not the volts that counts, it's the amps (or milliamps in this case). A small leakage current to earth is a "feature" of modern TV design (with switched-mode power supplies). The leakage is only a few milliamps, so isn't dangerous unless you have a heart condition.

However, as with all electrical devices, you should unplug before you meddle with the wiring.