I received this as a "bag of bits" it was in a cloth shopping bag with no screws holding the back and circuit board in place and the top and sides loose, no screws in the bag at all. Some components had been removed and some lifted to test? and then it had been put aside and left. I started by testing lifted components and then checked all the output transistors. They seemed to be good. I removed and replaced the missing electrolytic capacitors and replaced the other few anyway. I also tested the small signal and driver transistors and the (many) diodes. Missing was, on one channel, a bias transistor that is attached to the heat-sink and on the other channel a driver transistor, one of the pair; they were 2SD600K for the bias and the same for the missing driver (the driver pair are 2SD600k & 2SB631K). I replaced the bias transistors with 2SD639's that I had and then had matching drivers for both channels. All these transistors are difficult to buy new. I was trying to get the amplifier going with what was available so that I could test it more thoroughly. For reasons only known to the maker the bias transistors on the heat-sink are back to front i.e. the the side that normally touches the heat-sink and has a metal pad to facilitate heat transfer is facing away from the heat-sink. I initially fired the amp up using a rheostat, increasing the voltage slowly and found the quiescent current far to high, I had assumed the bias transistors would be the "correct" way around. After reversing the bias transistors the amp ran correctly and beautiful music emerged from the speakers, I adjusted the quiescent current (as a voltage on the test points) low and increased the rheostat mains voltage to full and then readjusted the quiescent to it's specification, no less than 10mV but preferably 17mV (designers usually specify a voltage across a resistor, usually an emitter resistor, that using Ohm's law, would give a suitable current in milliamps so as not to have to break the circuit to insert the current meter) Some of the problems with this repair were broken copper track to the output transistors, the copper looks a little thin.
An interesting oddity, the heat-sinks are not like any others in pictures I have seen on the net, these ones are bigger and longer, I'm not sure if they have been replaced or if they are original but a later? upgrade. Also the filter capacitors are all on the circuit board most seem to have two on the board and two clamped sideways to the chassis base. I believe an A250 is the same amplifier, but bridged, and they have all four filter capacitors on the board so I wonder if this is a later model A75, it says "is:3" on the circuit board. Anyway it does sound really good, very balanced with a lot of mid and high detail; bass? I've only had it running very small bookshelf test speakers but even then the bass is tight and full for the speaker size.