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Old March 30th 17, 08:23 PM posted to uk.tech.digital-tv
Benderthe.evilrobot
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Posts: 148
Default TV socket charge up


"Johnny B Good" wrote in message
...
On Thu, 30 Mar 2017 17:59:03 +0100, Brian-Gaff wrote:

I was plugging the aerial back in the back of a reasonably modern telly
last week and got a bit of a shock, well quite a big one actually off
the socket and the plug. the plug goes straight to an aerial, no amps or
anything so the whole thing has to be electrostatic I guess. I had
assumed once crts went that none of this sort of charging would happen
but it seems not.


I doubt it's static build up, Brian. More likely simply the quite common
effect of EMC filtering used by double insulated mains kit where the
chassis or 'common ground' is left floating at half mains voltage
courtesy of the high impedance capacitive voltage divider effect provided
by the EMC filtering circuit.


Can't remember the last time I saw one "left floating" - AFAICR: they always
have a tapped series pair of filter capacitors, and usually a resistor
voltage divider which bleed any charge from the capacitors.

The capacitors are rarely bigger than 4n7 and the resistors anywhere from
10M to 22M. The divider sets the double insulated chassis ground to half
mains with very high resistance - until you connect more
devices.................

The aerial socket is grounded to chassis ground, which is connected to other
devices by SCART or RCA leads etc.


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