Can anyone tell me when normally a leakage current test done and whats the reason behind it

and also What will happen if theres a absence of high voltage in a tv?

thanks

 

Leakage tests can be used to test insulation. It would be performed on capacitors, wires, etc., anything where insulation quality is of interest.

I'm assuming the high voltage you mentioned is the CRT anode voltage. In that case the CRT would be dark. The sound would still work.

 

I have a leakage tester for CRTs hiding in a corner covered with dust. It tests for current flow between cathodes and filaments and cathode and G1. (And cathode to cathode)

In an electron gun there is very little space between the first elements. Sometimes there is current flow that makes the color ‘funny’.

The leakage current should be in the 10uA range but if the gun is damaged current flows where it should not and there is no light or there is too much light. (out of control)

There are a number of failure modes for electron guns. If you want to get into the theories we can.