In message <19980315.172631.3254.0.mkeitz@juno.com>, Mike Keitz
<mkeitz@JUNO.COM> writes

Hi Mike,

>The *proper* common practice is to connect such a TV to an isolation
>transformer before operating it with the back off.  Then a properly
>grounded scope can be connected to the TV chassis without incident, and
>everything is grounded.  Lifting the scope ground is *not* safe.

We use isolation transformers on the benches at work, but I still
consider it safer NOT to have a scope grounded. It's all well and good
while you are working on an isolated supply - but it tends to give you
sloppy habits for the odd times when an isolated supply isn't available.
For instance, I don't have an isolated supply at home, so it's far
better to work in an earth-free environment.

>Another good safety practice is to never touch a live TV chassis with
>both hands (hold one hand behind your back).  Then if you do touch a live
>wire and get shocked the current isn't as likely to go through your
>heart.

Never touch any metal work without first testing it, just rub it gently
with the back of your finger, it will feel 'rough' if it's live.

>New TVs also often are of live-chassis design.  Higher-end models usually
>use a switching power supply that isolates the rest of the TV, but of
>course the power supply circuit is live.

Almost all new TV's in the UK are isolated chassis now, it fact I seem
to remember those EEC idiots passing a law that all new TV's have to
have a SCART socket fitted - this really requires the use of an isolated
PSU.
--

Nigel.

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