From time to time the incremental control wheel changes things by itself, and no turning of the wheel can yield an effect on the parameter that I choose to edit.
The parameter usually goes all the way to 99 and stays there. No matter if I turn the wheel CCW.
Looking at the schematic of board 6, I guess I should check for faulty 2N3904s or at the worst faulty MCT8s (availability)?
After checking whether the 5V for the board is being supplied correctly, of course.
The annoying thing about this quirk is, I can’t reproduce it, it just happens when it wants, so tracking the culprit down will be difficult.
I should add: All sockets of the regulators on the power board have already been removed and the regulators pins extended and soldered to the PCB.
Fixing the optos is tricky. After you put a new one in, you will notice that the solder holes are oversized. The physical position of both optos must be such that the phase of the signals represents rotation and direction to the control system.
I had to replace one opto years ago. Never measured the phase, I just re-melted the solder joints and moved the opto around until it worked.
I don’t know if a compatible opto is available today.
What effects did you have before swapping optos?
Did a parameter change by itself?
Just wondering whether a broken opto should be completely dead, and would never pass any data at all, or if it is possible it could be ‘half’ broken (resulting in effects I describe in the OP)?
Never passing data should result in a non functioning incremental control, shouldn’t it?
Maybe it is just knocked out of alignment somehow.
If anything is broken, I hope it is the 5V or one of the 3904s or anything besides the optos, for I already figured they would be the hardest to find.
Thanks!
Edit:
Let me add the described behaviour is only happening very infrequently.
And I only realised something was wrong when I was playing with the last parameter being cutoff turned way down and it slowly opened while I was playing the synth and I couldn’t stop it by turning the incremental wheel.
Misalignment, dust and hairs can mess with the optos.
The PCBs aren’t the world’s best either and the solder connections can crack.
Before suspecting bad components, you might try blowing it out with compressed air, check the soldering and if that doesn’t help, realignment.
The opto is an MCT8. There are other optos available in the same size, pinout and polarity, but I don’t have any cross-referenced subs for you. You’ll have to take measurements and search.
If you have a dual-trace scope, it’ll really help out.
Thanks! I will give it a good cleaning love and check soldering.
I had it open to swap the touch panel and to check the intermittent keys. Maybe dust got in the optos.
Concerning the keyboard: Once I checked how many keys are definitely failing, I am going to contact you, if you don’t mind.
Cheers.
