Thank you very much.
You are absolutely right. I will look into repairing it; the Mk1 is not supported by the manufacturer, so I am left with no choice but to ask a repairer in town.
I got a cheap BEATSTEP and started using it.
I have only assigned the track ON/OFF. volume yet.

I wish I could also assign Octatrack playback and stop, but I couldn’t find it in the manual.