I am repairing a TEAC AV-H500 amplifier but I did not find schematics.
First, there was no output in none of the 4 channels.
All the drive circuits are under the dissipator and the electrolytics capacitors of these circuits where all bad because they worked at too high temperature.
I subsituted all the 18 electrolytics capacitors and it came to life again....but I had very high output noise when I touched the preamplifier printboard.
I found bad solders at the connector....I solved this.
I found also bad solders in the two transistors from the protection circuit.
I had another problem: the dissipator was getting very warm (about 80°C) and the amplifier was going in protection.
To try solving this, first I lubricated the fan dc motor (Matsushita MDN4RB4MRC) who was making noise, then I increased the fan speed by changing a resistance of the voltage divider of CTN temperature sensor from 220R to 1K.
It is still going in protection after about 10 minutes of working.
I did not found any iddle current trimpot , nor any way to measure this iddle current of each of the 4 channels.
Without schematics, I can't go further.
Thank you very much for your help....