Hi,
Using the deflection coils to make the line or dot move around on screen
will certainly work, but the problem is with the inductance. There is just
too much inductance to get any real speed going there. The TV normally
operates at less then 20kHz, so you might get that if you are lucky and
do everything just right. You wont get anything like a real scope though,
which has bandwidth beyond a megahertz. Maybe you only want to look
at low frequency signals?
If you really want to use a TV as a scope, then your best bet is to design
a digital scope (fast ADC and memory) and use that and generate a composite
TV signal that shows that wave on the TV screen. It wont be that good
but it will be fast. Better yet, use a computer monitor as you'll get better
display resolution.