Alesis s4 plus - trying to troubleshoot

So I got a used s4 + that has some problems. While it responds to MIDI, and I can switch patch from the page and bank buttons, I am having problems with the GLOBAL and MIX buttons - hitting them both does not start the DEMO, Switching from patch to mix doesn’t work. I tried reseating the flat cable at both sides, cleaning connect with deoxit, etc.

Any ideas? Any S4 + repair manual out there?