I recently just purchased a Yamaha C-65 and Yamaha M-85 for $80 and they are in need of some repair. I'll eventually make another thread for the M-85.
I am new to electronic repair and, if possible, I would like to attempt to repair the unit I just bought. I am linking some pictures of the board and attaching the service manual as well. Below I note things I see wrong. But really I don't know how to start. Do I just start replacing components? Will I still be able to use the board even though a portion of it seems to be burnt? I turned it on and plugged in some headphones and it is still operating. Though, I could immediely smell something burning so I turned it off.
Any help would be greatly appreciated.
Here is an overview shot of the L and R MC AMP
The right Main Channel Amp portion seems to be burnt.
The left Main Channel Amp is starting to do the same thing. Also I noticed that some carbon resistors were starting to turn black.
It also looks like some of the capacitors are starting to bulge.
They are Electrolytic Capacitors 4700 uF 35V
I am new to electronic repair and, if possible, I would like to attempt to repair the unit I just bought. I am linking some pictures of the board and attaching the service manual as well. Below I note things I see wrong. But really I don't know how to start. Do I just start replacing components? Will I still be able to use the board even though a portion of it seems to be burnt? I turned it on and plugged in some headphones and it is still operating. Though, I could immediely smell something burning so I turned it off.
Any help would be greatly appreciated.
Here is an overview shot of the L and R MC AMP
The right Main Channel Amp portion seems to be burnt.
The left Main Channel Amp is starting to do the same thing. Also I noticed that some carbon resistors were starting to turn black.
It also looks like some of the capacitors are starting to bulge.
They are Electrolytic Capacitors 4700 uF 35V
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Your main caps are likely fine, but I'd be replacing them after you've sorted out the problems. There's also a small cap very bulged next to one of the cooked 1 watt resistors in the second last pic.
It looks like a bunch of nasty looking dry joints under the PCB too. I'd be starting with all the PSU rails, checking they are not running way too high (+/-16v and +/-20v in that preamp) after isolating them one at a time after repairing the carnage of the dead resistors/caps/transistors. Check the caps immediately near the heat producing components. It doesn't look too bad, that board damage is not as bad as some.
Grab the S/M if you don't have it.
It looks like a bunch of nasty looking dry joints under the PCB too. I'd be starting with all the PSU rails, checking they are not running way too high (+/-16v and +/-20v in that preamp) after isolating them one at a time after repairing the carnage of the dead resistors/caps/transistors. Check the caps immediately near the heat producing components. It doesn't look too bad, that board damage is not as bad as some.
Grab the S/M if you don't have it.
Great, thanks for the guidance. I will be ordering components soon.
What is S/M?
Board discolouration is normal for hot running parts, but what you there is way beyond that stage as the board is starting to carbonise. The problem with that is that it can become conductive, which admittedly is more of an issue in high voltage circuitry... however.
Your first check has to be that the main unregulated rails are correct. If they are noticeably high then that will cook the following circuitry.
The print in that really burnt section will probably be unworkable with the foil lifting and the solder not 'taking'. Repair in those cases is still possible and involves drilling or cutting out the burnt section and hardwiring the components into place. That can be done neatly, it needn't look messy, and any large gaps can be filled with epoxy putty for mechanical support if desired.
Your first check has to be that the main unregulated rails are correct. If they are noticeably high then that will cook the following circuitry.
The print in that really burnt section will probably be unworkable with the foil lifting and the solder not 'taking'. Repair in those cases is still possible and involves drilling or cutting out the burnt section and hardwiring the components into place. That can be done neatly, it needn't look messy, and any large gaps can be filled with epoxy putty for mechanical support if desired.
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