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Fault
High DC on both speaker terminals plus 2.65 Volts.

The NAD302 does not incorporate a speaker protection circuit.
Hence high DC can be present on the speaker terminals potentially damaging the speakers.

A visual inspection of the Amplifier circuit board quickly identified that R513 1K5 1/4 Watt resistor was burnt, indicating at an issue with the plus 38 and 28 Volt DC supplies.

R513 was replaced and further checks made, R511 10 ohm 1 watt resistor was open circuit, replaced.

C518 220uF 50 V Capacitor short circuit. (Luxon)
All Luxon capacitors in the power supply replaced to avoid further issues.

Q507 2SC3421 leaky emitter to collector, replaced.

Dry joints on Q509 2SC1815 , Q508 2SB649, Q511 BD139.

Amplifier powered up and retested, high DC on the speaker terminals no longer present.

Fault 2
Loud buzzing sound on the Tuner and Phono inputs when a test signal applied.

Usual fault due to dry joints on the input RCA connectors. (Loss of the ground connection)

Rear back panel removed and all RCA input sockets re-soldered.

User controls and switches cleaned with De-Oxit.

Amplifier fully tested, working correctly.