Vintage Synth Repair

Hi everyone.

I have a Matrix 1000 that I am trying to bring back to life.

The issue is as follows:

I can turn it on just fine but it will freeze after a few minutes , this happens even though I just leave it alone.
Sometimes it will also randomly change presets but that does not happen often.

I have reseated all socketed chips,checked that battery, done the initialization but it keeps freezing.
CPU has been changed (I have two more CPU´s) * Software is 1.11

Any thoughts ?

Thanks
Arnar