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I would check TR87 on the switch board. It is the switching transistor that controls the regulator in the power supply. Looks like most any general purpose NPN transistors (nte123a) will work on that board. Looks like there is an oscillator (which you control with the touch pad) then a wave shaper, two stages of squaring amps, a two transistor flip flop trigger, then a switching transistor to control the main voltage regulator (TR71) through a 10 ohm resistor (R826). Looks like it would have been much cheaper and easier to just leave all that rube goldberg circuit out and use a regular switch in the primary of the power supply transformer. I tried to scan the schematic, but my obsolete hardware is refusing to cooperate today. It is in Sams 1384.
Good Luck
Bill R
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