Now I was working with a deck that was originally working and has no cracks. I managed to restore her work completely, which I am very happy)) She just started working. I rearranged the diodes D720 and D702 and the correct power supply was restored on the basis of the Q 712 and Q702 transistor. But now I need to buy similar diodes in order to return them to the second board. Which ones should you buy? I also need a Q710 motor driver for the second board, what is the analogue? Thanks!
JVC M90 didn't work cassette deck (photo coupler problem?)
- Thread starter brovKO
- Start date
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
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
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Make sure the photo sensor led is turning off after it does it's check.
Mine was staying on all the time.
It looks like the record led driver is in ic704 c.
Verify your readings are the same between both boards on that ic.
As far as the q712 transistor is concerned, I know they get hot but I would buy the original 2sd439 since they're cheap enough and easy to find.
My music search wasn't working, it turned out to be q506's legs were rotted away, I made a post about it with pics https://boomboxery.com/forum/threads/jvc-m90-mms-music-search-problem.30972/
Keep at it, you're close.
Mine was staying on all the time.
It looks like the record led driver is in ic704 c.
Verify your readings are the same between both boards on that ic.
As far as the q712 transistor is concerned, I know they get hot but I would buy the original 2sd439 since they're cheap enough and easy to find.
My music search wasn't working, it turned out to be q506's legs were rotted away, I made a post about it with pics https://boomboxery.com/forum/threads/jvc-m90-mms-music-search-problem.30972/
Keep at it, you're close.
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