Hi,
cant remember where I read this but I thought there was a danger in using an
oscilloscope to check a TV sets signal due to the chassis being directly
connected to mains or something like that - is that right, if so how can one
use a scope for the purpose?
thanks
Sean
It is right that in most OLDER TV sets the chassis was 'live', usually there
was a bridge rectifier and the minus connected to it.
Other configurations existed.
Then later came the TV sets with video input etc.., these have a separate
mains supply unit, that separates the set from the mains.
In a workshop you should ALWAYS use a 1:1 mains separation
transformer of ENOUGH watts, and that maybe as much as several hundred for
old sets.
I admit to doing it without on occasion, but also got alomost killed that way.
So, ground your scope, use a separations transformer.
You should make sure the secondairy does not drop if loaded with a set,
some old sets, for example the Blaupunkt thyristor ones, chopped up so bad that
even a 350W transformer started to smell..
This is because the losses are i^2 x R, and rectifiers and other stuff draw only
current in a small part of the wave, and then much more then it would be if
it was a purely resistive load.
JP
Copyright Jan Panteltje 2004 All Rights reserved.