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

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. 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

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

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. 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"?
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

"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

Jim Yanik wrote in message
...
"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

Could you explain to a Limey what a groundbuster is and I'll add to this "2
nations divided by a common language" file

UK / USA Tool Terminology Translator
http://www.divdev.fsnet.co.uk/tool_terms.htm

N Cook wrote in message
...
Jim Yanik wrote in message
...
"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

Could you explain to a Limey what a groundbuster is and I'll add to this
"2
nations divided by a common language" file

UK / USA Tool Terminology Translator
http://www.divdev.fsnet.co.uk/tool_terms.htm



I take it from Googling that a ground buster / groundbuster is an adaptor
that simply converts a 3 prong AC plug into a 2 prong.
In the UK they don't exist as such , the third earth/ground pin is needed to
open the safety sliding shrouds covering the powered sections of the socket.
"wall warts" for the UK always seem to have plastic earth/ground pins which
have to be there as dummies so you can physically plug into UK power
sockets.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

rogersk8ter wrote:
snip

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

If you have to ask, it's MANDATORY - NO EXCEPTIONS !!!

GG