JVC Amplifier Repairs
The graphic display wasn't working, one channel wasn’t working in stereo mode and the inputs were on all the time. Resistor 10 ohm had blown to the regulator, two capacitors were shot 2.2µF 50 V on the power amp and the input IC TC9164 needed replacing.
This needed the output transistors replacing as several were short cct collector to emitter. The originals had a higher Vbe than the modern replacements I was using which would have upset the power distribution if I had just replaced the faulty ones, sounded fine after repair. A 100W/ch rare power amp from the 70's.
This one worked but checking the o\p DC voltages - they were all over the place. The now normally faulty transistors Hitachi '2SC1345' were the culprits. Two in the differential input stage of each amp, setting the quiescent and o\p 0 V was easy after this. A very well made amp manages 90 W a channel in 2 ch mode 40W/ch in 4 ch mode and weighs a ton!
This one was giving no o\p, the o\p of one of the rectifiers goes to the RH power amp through the PCB (on edge connectors) and then to the smoothing caps, one of the edge connectors had burnt a hole in the PCB track and lost one of the supplies, there was 4 V on the speaker o\ps, a better way would be to go straight to the caps then to the L\R channels, this is a massive receiver from the late 70's, 110W\ch - count those components - okay so there's not that many.