You asked for a recommendation. You always can do different anyway...
Opening a unit, finding a flaw that probably could not be fixed with simple tools is just useless effort. In addition there are legal issues with guarantee it you take things serious.
So what's my message? Simply avoid useless work and trouble.
"Electronic music" does not mean that we can understand complex electronics by just opening it... then looking at black chips... that's quite useless even if you have an engineering degree... also pro technicians often can't do much, finding errors in such devices... it's too often complex and too time consuming to be done seriously... then we are back to "PC" repair strategies... well, lets exchange this and that and see if it works again... that's where we end up too often when it comes to "repair" of our beloved electronic gadgets... engineered to be "affordable" (referring to complexity) and... one way.
If anyone is able to find the real errors in a device at all it would be the manufacturer - but then again, a specialist from there is needed for new development and would be even more expensive doing this job... working hours in germany are expensive... so expensive that even germans can hardly afford them...