That’s R18 right? Powered on at rest it’s measuring at about 9.6K. When I play around with the midi keyboard it drops a few K down to as low as 3.5K. I don’t suppose swapping it for a lower value resistor would work?
Please don’t swap anything until you find the culprit! The system is designed to work correctly and tweaking values won’t do any good, you need to find the root cause.
At this point you’ll need an oscilloscope to check the optocoupler output signal.
Try to lift/bend the display a bit and then send MIDI notes. Might be MIDI socket is shorted below display?
Well, I irreparably destroyed the solder points trying to get the display off, my own stupid mistake. I know it wasn’t necessary to take the whole thing off, but I’d wanted to lift it closer to the enclosure anyway. Guess I’ll have to order another pcb sometime and salvage whatever components I can from the damaged board. I really hope I don’t run into the same midi problem. Does anyone have tips for desoldering encoders and switches?
Personally I wouldn’t bother, there’s nothing worse than reusing components only to find out you’ve fried them in the process.
But tact switches can be removed with a decent desoldering tool. Once you’ve sucked out a lot of solder, get some pliers and tweak the switch by turning it clockwise and anti-clockwise, it should then be able to be pulled out.
Thanks, it’s really only the encoders and switches that I want, and they’re easy enough to test. I’ve got no qualms about cutting the board up to make it easier now.
It’s only really possible with a desoldering station in my experience.
I’ll see how it goes but won’t put too much energy into it for now. Time to focus on building an MB-6582 and come back to the XT at a later date.
Necrobump alert After shelving my troublesome Shruthi XT build for over a year and successfully building a MB-6582 in the meantime, I’ve finally returned to the Shruthi after populating a new motherboard PCB with new components. However, I’m reusing my original:
- Pre-programmed ATmega chip from Modular Addict
- SMR-4 filter board
- ICs except for the 6N137
And… I discovered I still have the original problem, i.e. the midi in not working properly. It recognises something coming in via midi, but nothing useful. So, I’m kind of stumped. I’m confident that my solder joints on the motherboard are good enough. Is it then likely to be a problem with the filter board or ATmega chip?