No power

A TGS200 that's lasted this long?????? You're very, very lucky indeed.

When I worked on these things many, many years ago, common failures were in the HV power supply. But by now it could be anything . . .

There also might be an internal fuse that would probably be very easy to see if you removed the cover....or a fuse hidden in the power connector.

Look for the obvious....you will catch 90% of the problems...

As a former electronics technician the first question is always, are all the connections solid and is it plugged in.
I am sure you have checked these but it is the first place to look.