Probably OT: voltage appearing on TV SCART socket

[Nick Leverton]

Hope you'll excuse this query although not strictly a DIY question - uk.diy is probably one of the more savvy remaining newsgroups ! I want to know whether I'm interpreting what I am measuring correctly, about getting shocks in the following setup.

Daughter recently bought her sister and us a couple of flat screen tellies from Argos. Ours is connected by SCART leads to a PVR and a DVD player. The TV is also connected by aerial lead through the PVR to a TV amplifier and distribution system.

Since setting it up, I've been experiencing slight shocks when touching any of the aerial cables in the house. After some investigation and reconnecting things one at a time, I've found out that when the new TV is plugged in, a significant voltage appears on its SCART shield - my cheapo multimeter measures it at about 49V to earth. This is then propagated through the other devices and gets to the aerial cable, it seems.

I installed the TV amp+cabling myself and have checked that the amp itself is not the source of this voltage. In fact the amp's output sockets are connected directly to earth (as checked by multimeter), but the connection is apparently not good enough to pull the voltage injected by the TV down to 0V. And I wouldn't expect it to be, those co-ax push-on connectors are not designed to be earthing paths !

At the root of the problem, it doesn't seem right to me that a TV can put what looks like a low resistance path to live onto the SCART shield. I know that CRT TVs often used to have floating chassis, but I've checked our two remaining CRTs and their SCART sockets are firmly neutral. I've compared both the new LCD TVs and both show this problem.

The model is Toshiba 32BV500B so not really a cheap fly by night make, hence I'm keen to make sure of my facts before going steaming back to Argos - I don't want to make un-necessary hassle for daughter as the purchaser. So am I reasonable in assuming this indicates an electrical fault with them - apparently by design since both TVs show it ? Or would you expect SCART sockets to carry a significant voltage in some circumstance ?

Thanks for any advice, if you know of a better newsgroup that isn't just a spamfest by all means point me to it :-)

Nick

[John Rumm]

Does the TV have a three core or two core mains cable? (and does it carry the double insulated logo[1])

There is a fair chance the TV has mains input filters, that may couple the chassis to the supply via a capacitor network. On unearthed equipment this will mean the chassis will tend to float at half mains voltage - although the current available in very low, and you should be able to pull it down to ground easily.

[1]

[Tabby]

its a high impedance path

Solution, as said before, is to earth either at the tv or the other end of the cable that goes to the tv. Its a commonish issue. If you dont it wont harm you.

NT

[geoff]

Harry, ssshhh

your half grasp of a bit of knowledge is a dangerous thing

If it was static, then earthing it would allow the static build up to dissipate. The tingle is normally due to leakage in filtering capacitors