Shruthi firmware freeze on midi in

hey guys,
someone asked me if i had an idea what’s wrong with their Shruthi. he sent a short video and it looks like the firmware is freezing as soon as there’s midi in. everything works fine until midi starts, then no button / knob function anymore.
so i think it’s not the MCU but rather something around the opto. any ideas maybe?

Still too dumb to post videos here :wink:

Try swapping in a 6N138 instead of the 6N137 ; increase the value of the 10k pull-up on the optocoupler out ; or swap the 644p.

thanks Olivier

Had problems with MIDI in.
Shruthi made reboot after some time.
I changed the 20MHz Quartz and problem solved.