Hello! After several days of continuous and incredibly difficult work for me, I repaired the board with a crack. I replaced the transistors R720, R712, R711, R726, R728, R722, R747 and some more, I also restored several traces. I interrupted the printed transistors additionally with a sharp knife (so that there was no parallel resistance, as I was advised). Instead of a faulty Q710 motor driver, I installed a BC635 (I found information on the forum that this transistor is suitable).
After repeatedly checking the readings of all the replaced transistors and comparing them with the readings of the transistors from the working board, I started the deck. The solenoid began to click, the motor was spinning, and the photosensor was glowing, it's incredible!))
I just installed the board on the deck, connected everything and started testing. Playback works, pause and stop work. Rewinds work the same way. But when I press the play key, the deck starts playing, but the record LED turns on. If during playback I press the rewind key, then this LED turns off and rewind starts, when I release the rewind key, playback continues, while the LED does not light up anymore, but as soon as I press the play key again, the LED starts to glow again. In addition, it seems to me that the auto-search function for audio tracks does not work. To make it clearer, I shot a video and add a link to it.
I am also a little concerned that the 12 Volt Q712 regulator heats up very quickly to 115 degrees Celsius (240 Fahrenheit) while the deck is running, and I think it might get hotter if the deck is used for longer. It seems to me that this is too much. What is the way out of this situation? Is it possible that the regulator is defective? Although it produces 12 volts as expected. Can a cooling radiator be attached to it? Or is it better to make a replacement? Can BD139 replace Q712?
VIDEO JVC M90 deck testing
