"rogersk8ter" wrote in
ups.com:


N Cook wrote:
rogersk8ter wrote in message
ups.com...
Im trying to scope a TV signal. Where should I ground the probe's
ground? Over the common ground on the PCB board? Isn't that a
floating ground?

There seems to be 30V ac with reference to the scope ground when I
use a VOM to measure voltage.

Don't forget DCV;the chassis can be as much as 170VDC difference from
earth ground for a 120VAC line supply.


Will it blow or damage the scope?
Anyway to prevent sending live current down the scope ground and
blowing it up? Thanks.


The first thing you do is obtain an isolation transformer 110/110V or
240/240V that allows TV to float up or down relative to the scope
ground. Second you learn about the potential (in both senses) dangers
associated with TVs

--

Can I just ground t to the TV chasis? Where the springs is? Or a
isolation transformer is a "must"?


It's a MUST. Repeat;a MUST.

TV chassis can be electrically hot WRT earth ground.
Just look at any switching power suppply schematic.
There's no ground,instead "common".

Hook your scope ground to it and you blow the TV and/or your scope,make
lots of sparks and smoke.

Or your scope case becomes electrically hot and you touch it and a real
ground,you get electrocuted.(that's why you don't use groundbusters.)

--
Jim Yanik
jyanik
at
kua.net