Nakamichi Amplifier Repairs

Nakamichi 420 Power Amplifier

Nakamichi 420 Stereo Power Amplifier Nakamichi 420 Stereo Power Amplifier

This came into the workshop with the right channel not working. I discovered the fuse had blown. I checked the output transistors which are the small MT100 type and one had blown. Checked the operation of the amp by wiring a TIP transistor temporarily in circuit, didn't work correctly, so there were more faulty components. This made it questionable if it was economic to repair as the original transistor would cost £20-25 each! I looked to find a more economical route and ended up removing the old transistor moulding from the metal tab and glueing a TIP42 transistor on it with thermal adhesive, there was also a transistor open circuit in the driver section A915. It sounded okay after repair.

Nakamichi 410 Preamplifier

Nakamichi 410 Stereo Preamplifier Nakamichi 410 Stereo Preamplifier Nakamichi 410 Stereo Preamplifier

This was as dead as a dead thingy! Turned out the mains transformer was cooked and needed replacing. I could tell by the burnt smell when the case was opened. The supply voltages to the circuit were +/- 5V where they should be around 10V. The Zener was also cooked at 3.6V and just for good measure the power lamp needed replacing too.

Nakamichi Amplifier 2

Nakamichi Amplifier 2 Nakamichi Amplifier 2

This had blown the output transistors, drivers, temp sense transistor and a few resistors 100 ohm, 330 ohm, 1 ohm, and the 1k bias pre-set.