Shock off DVD player - case showing charge

[Desie]

My wife and I both got a shock off the ariel cable that was plugged in to the DVD player yesterday. Using a neon tester I have detected a charge in the ariel socket and back plate of the DVD player and the freeview box individually. I assume we got a shock because we earthed it.

I've had the back off the DVD and there doesnt seem to be anything amiss and the fact that both appliances seem to be carrying a charge independently tells me something else is causing the problem.

I have also checked the earth on the socket and that is fine.
Neither appliance is earthed.

3 questions
What would you say is causing the charge?
How do I measure the charge using a multimeter?
How do I stop it?

thanks

 

[councillor]

Is the circuit your connecting the DVD player/ freviewbox RCD protected?

Im not an expert but if there is leakage in any of those items then surely the RCD would operate. If the socket is not RCD protected then this may explain why you get a shock

like I say Im not an expert by any means so lets hope one of the experts has a view.

 

[ryanjuk87]

I assume we got a shock because we earthed it.

Is the appliance double-insulated (two-core flex, no earth in plug)? If it is it should not be earthed.

 

[stevesey]

Was that the UHF in or out - wouldn't be suprised at getting a minor tingle of the UHF out - that's just the signal (even though it's only small I think at that high a frequency our impedance drops so we feel the shock more than the few mVs would suggest).

Also what are you measuring between? It's likely that signal ground is floating w.r.t earth and/or chassis.

And what were you measuring with? - Modern high impedance DVM will happy read induced voltages in unconnected wires (try and draw any current what so every and the voltage is slugged).

[Edit] Ah - I see you haven't measured it yet. Confused by the statement that both units were carring charge - can you clarify what you mean.

 

[Desie]

stevesey

I am picking up charge with a neon scredriver/tester.
I have a multimeter but not sure how to test for this charge. There is no charge between this and an earth connection.

Ryan
The appliances are both double insulated and so don't have earth connections.

How do I measure what this current is?
How do I get rid of it?

Thanks

D

 

[stevesey]

stevesey

I am picking up charge with a neon scredriver/tester.
I have a multimeter but not sure how to test for this charge. There is no charge between this and an earth connection.

Ah Neons - easy to be mislead by them. Try waving one around inside the back of a TV (carefully!!!) the high frequency magnetic fields will get them to light. In fact if they don't light near certain components this is a good indication of a failure.

Try using the neon on different corners of the case - won't be suprised if you get different brightness at different locations.

 

[Desie]

Stevesey

I know nons are not the best tool in the world but it is the only thing I can test with in the absence of anyone else telling me how I measure the charge thats going through the back of this appliance.

I can assure you there is a charge as both my wife and I are getting shocks off both the DVD and Freeview box.

Can anyone please tell me what is going on, how I test for it and how I get rid of it?

Ta

 

[Lectrician]

As these items are not earthed, the screen of the aerial and chassis on the items are connected to neutral via a capacitor and other circuitry to remove interferance. Often a reversed polarity will put 240v onto the chassis on older machines. New machines are designed to not allow this to happen, but can still have some volts on the chassis - but it has current limiting circuitry.


The way to get rid of this is to intentionally earth the screen of the aerial somewhere - just one point will do - Loft, Wall outlet etc. all screens will then be earthed as you plug your items together. The screen should be earthed, but often is not.

I am not an expert at all on the insides of VCR's etc, but I have explained it as best I know how!

To meter it, connect one prong of your volt meter to true earth - the earth pin of a socket, a radiator etc. Put the other on the chassis/screen. Set the meter to AC volts.

 

[Desie]

thanks Lec
Help at last!!

 

[stevesey]

... Often a reversed polarity will put 240v onto the chassis on older machines. New machines are designed to not allow this to happen, but can still have some volts on the chassis - but it has current limiting circuitry..

Don't forget to check for reversed polarity (socket and plug) and correct if necessary.