Electric shock from STB

For some years now TVs, and STBs, have been required to place a high value
resistor network across the mains, with the centre point "earthed" to the
box.

Fascinating! That explains why all my kit under the telly gives a little
"buzz" when I brush the back of my fingers over the case. (I mean you can
feel the buzz, not hear it, but I can't think of a better term).

Why do they do this, any idea?

SteveT

In article
,
Mark Carver wrote:
On Feb 8, 8:47 am, Dickie mint
wrote:

For some years now TVs, and STBs, have been required to place a high
value resistor network across the mains, with the centre point "earthed"
to the box.

Indeed. There may well be 100 volts there, but there'll be bugger all
current available, and that's the all important difference.

Some years ago, I measured the current from my VCR which was exhibiting the
same symptoms. Current was no more than 50 microamps!

--
From KT24 - in "Leafy Surrey"

Using a RISC OS computer running v5.11

On Fri, 08 Feb 2008 09:37:04 GMT, "Brian Gaff" wrote:

Normally this is to discharge the capacitors of any interference
suppression networks, but they usually pick a very very high value, and if
they don't the tingle is the result.

Brian

It is primarily the current passing through the capacitors themselves, not any discharge resistors,
which aren't necessary for the small values of capacitors typically used in the live-to-earth
position.

This is common. The box is double insulated so the aerial shield floats up
to 120V AC.


"Agamemnon" wrote in message
. uk...
I have discovered that the casing and aerial socket of a cheep Mico STB238
STB which my dad bought last year is 120V AC (half mains voltage) above
Earth potential when I tested it with a meter after it kept giving me
electric shocks every time I plugged the aerial in and out.

The plug on the box does not have a wired earth and just has L and N going
into the mains.

Does anyone have any idea what could be causing this voltage. Could the
Neutral or the Live be connected to the metal casing of the box via a
faulty bridge rectifier. Why is it 120V and not 240?

What should I do with box? I don't particularly want to keep using it
since I think this may have been the reason my dads video recorder got
fried a couple of days ago since it was plugged into the aerial out from
the box.

In message , Brian Gaff
writes

For the record, I don't like it either, but I've noticed it on some hi fi
seperates, even some made by Sony.
I love the way you imply that Sony should in some way be better than
other makes.

Brian


--
Clint Sharp

Steve Thackery wrote:

Why do they do this, any idea?


I'd, too, love to know the source of the regulation.

Back in 1998 was when it came to my attention, when the AV technician
asked for more money for aerial isolators for my new STB and monitor
stack in Pebble Mill, as we set up Digital TV Support monitoring. He'd
seen it in some journal, and I never photocopied it or made a note.

subsequent google searches never found it :-(

Richard

Adrian wrote:
Mark Carver wrote:

Indeed. There may well be 100 volts there, but there'll be bugger
all current available, and that's the all important difference.

My Daewoo Setpal box does this (as I found out the other day), but
despite being a little unpleasant, it's no more dangerous than
sticking your tongue on a PP3.

What is the likelihood of getting this when fiddling with the aerial or coax
wiring? What might not be dangerous in a room might be a bit dodgy on a
roof.

--
Jeff
(cut "thetape" to reply)

"charles" wrote in message
...
In article
,
Mark Carver wrote:
On Feb 8, 8:47 am, Dickie mint
wrote:

For some years now TVs, and STBs, have been required to place a high
value resistor network across the mains, with the centre point
"earthed"
to the box.

Indeed. There may well be 100 volts there, but there'll be bugger all
current available, and that's the all important difference.

Some years ago, I measured the current from my VCR which was exhibiting
the
same symptoms. Current was no more than 50 microamps!

What happens if you connect in circuit an appliance that really is earthed?

--
Max Demian

Dickie mint wrote:

Steve Thackery wrote:

Why do they do this, any idea?


I'd, too, love to know the source of the regulation.

Back in 1998 was when it came to my attention, when the
AV technician asked for more money for aerial isolators
for my new STB and monitor stack in Pebble Mill, as we
set up Digital TV Support monitoring. He'd seen it in some
journal, and I never photocopied it or made a note.

subsequent google searches never found it :-(




I remember someone from PACE asking the same, and the only
conclusion I could think of was for a static leak for the
metal case.

"Max Demian" wrote:

"charles" wrote in message
Mark Carver wrote:
On Feb 8, 8:47 am, Dickie mint wrote:

For some years now TVs, and STBs, have been required to place a high
value resistor network across the mains, with the centre point
"earthed" to the box.

Indeed. There may well be 100 volts there, but there'll be bugger all
current available, and that's the all important difference.

Some years ago, I measured the current from my VCR which was exhibiting
the same symptoms. Current was no more than 50 microamps!

What happens if you connect in circuit an appliance that really is earthed?

Then that 50uA flows to earth. :-)

--
Dave Farrance