So, the #Ensoniq #ESQ1 adventure continues. Turns out that the battery is still okay even, going to replace it anyways. The keys have/had bad contacts, which can be fixed by applying lots of contact cleaning spray containing funny chemicals.
The synthesizer stuff works like a charm apparently, I'd have expected issues there. Also the capacitors look alright.
But now I found out that the display isn't weird, it's broken. Some people in forums say I need to replace the display controller chip, which is out of production…
This might turn out to be a tough one.