G'day, an experienced technican would use an isolation transformer as your set is a live chassis, that is above earth, if you don't have access to an isolation transformer be extremely careful and try the following. Making sure that the set in unpluged from the mains supply (power point) remove the rear cover and then attach the normal input that is aerial/component etc, plug into mains and let it soak (run until the fault appears, sometimes I have used a hair dryer to generate excessive heat to induce the fault) when fault appears I would use Freeze (a can of freeze can be purchased at any spare parts supplier or even Tandy's) to various components to see if that fixes the problem.
To locate this area look for when the CRT (cathode ray tube) EHT (extra high tenion) plugs into and follow that down to the boubler/tripler and flyback/line output transformer. The high voltage that is residual after turning set off is the EHT and in most sets there is a flat spade that attaches to the aquadag (metal cover surrounding the CRT (also called the picture tube) via a twisted wire connector, I doubt if you would need to use this. I hope I have given you a couple pointers mate. cheers gazza