I would first thoroughly investigate the area around the mains input circuitry checking that the internal fuse is tight in its holder etc, then switch the set on and with the aid of a LONG plastic or nylon rod and whilst exercising extreme caution! lightly touch all the components centered around the fuse and the ones obviously connected to it. (WATCH THAT YOU DO NOT BRUSH AGAINST THE TUBE OR THE EHT LEAD CONNECTED TO THE SIDE OF IT WHILST CARRYING OUT THIS TEST) If you cant get it to flinch by touching anything, with the set having been unplugged for about 30 minutes to discharge any capacitors simply touch up all suspect looking PCB contacts with your soldering iron, there isn't really any magic cure other than carrying out that sort of procedure.