jrz126 said:
I'm working on repairing/diagnosing my oscilloscope, since Im dealing with the CRT power supply, the service manual recommends that I use an isolation transformer. I dont have a plain transformer, but I do have a 0-140V varac.
Is it ok to use this? and there is no ground pin on the varac itself, can I operate the scope without the ground connected?
I was thinking about just running a wire from the ground on the scope to the ground on the wall outlet. I figure it's better than running it without a ground, but I dont know if that will unisolate the scope.
I'm working on it as I'm typing this, so please respond ASAP if you can help.
If you're still alive? :lol:
A variac provides NO ISOLATION AT ALL, it's only a variable tapped auto-transformer. So it would be totally popintless using it!.
Working on non-isolated mains just requires a little care, a good idea if you're inexperienced is to keep one hand in your pocket - but this applies with an isolation transformer as well.
The most important thing is probably to understand what you are doing, and why, this will lead you to safe practices.
There are basically two schemes of thought, one is to use isolation transformers and everything earthed - the other is to not use a transformer, but work in a completely earth free environment. They are probably both as safe as each other.
Personally I'm quite happy (and confident) to work in a live mains unit with no special precautions - but I've been doing this professionally since 1971!.
One thing I ALWAYS DO, and it's a point of some contention!, is NEVER use an earthed scope - all my scopes have the earth leads removed, and are clearly marked as such. I consider an earthed scope too dangerous to use!.
I don't suggest YOU do this, unless you are fully aware of the reasons behind it - but it's commonplace in the TV service trade, and always has been.