This is exactly the service manual I needed.
Complete with all schematics, partslists, PCB layouts and alignment instructions.
This manual covers both the T-4970 en T-488F Onkyo tuner.
Text excerpt from page 3 (click to view)
Check that exposed parts are acceptably insulated from the supply circuit before returning the repaired instrument to the customer.
Measure the resistance value between the both poles of attachment cup (power supply plug) and the exposed parts (parts such as covers etc. where the customer can easily touch) and check that the resistance value is 500k ohms or more.
The following precautions should be observed when servicing. Since many parts in the unit have special safety related characteristics, always use genuine HITACHI replacement parts. Especially critical parts in the power circuit block should not be replaced with other makers. Critical parts are marked with a ! in the circuit diagram and printed wiring board. Before returning a repaired unit to the customer, the service technician must thoroughly test the unit to ascertain that it is completely safe to operate without danger of electrical shock.