Fault
Amplifier powering up, but the main display was not illuminating.

DC supply voltages checked, the minus 24 Volt supply when measured at the collector of Q702 was found to be low at 0.2 Volts,.

The Voltage at the base of Q702 was also low at 0.2 volts, the voltage at the collector was minus 39 Volts.

Q702 forms part of a series regulator circuit.
D713 MA4180MTA connected to the base of Q702
(24 Volt Zener was found to be short circuit)

Replacing D713 restored normal operation.

Usual dry soldered connections on the input RCA sockets
re-soldered and the main Audio output IC, and power supply regulator transistors mounted on the large heatsink..

User controls cleaned with Servisol Super 10 switch cleaner.

Note: The volume controls original lubricating grease had dried out making it very difficult to turn.

Servisol had to be sprayed around the shaft of the volume control and then worked back and forth until the control rotated freely.

Amplifier fully tested working perfectly.

свернуть