hey there is an actual branch of engineering for this.. it's called mechatronics...!
Electronic circuits are only part of the game for major process equipment.
Some typical sub-systems for one machine:
Vacuum: mechanical rough, turbo, and cryogenic pumps. HE compressors and pumping. Low/High vacuum gauges, piping, various fittings and leak detection.
Gas: Flow metering (MFC), pressure sensors, Plasma generation (Ion source), waste capture/leak detection systems.
Cooling: Glycol, DI water pumps, heat exchangers, DI filtering and O2 removal. Water RS purity monitoring.
Electrical: Mains, high current low voltage for beam bending/ shaping magnets (10KG+), high voltage for beam acceleration (250Kvdc+), electrostatic scanning, RF amplifiers (30Kw)for final energy acceleration (1Mev+) , computers and controllers.
Mechanical: wafer transport robots. spin/flip beam orientation motors/gear boxes. Gyro tilt motors/gears, DC servo, AC servo, stepper motors, linear motors/bearings. Vacuum shaft couplers, ferromagnetic couplings.
Pneumatic: Vacuum/vent/purge valves,wafer lifts, motor cooling, process chamber doors/load-locks.
The list goes on forever.
All of these things have to be repaired, pm'd. When we look at a new hire, I tend to spend more time about asking about wrenching than electronics.