Hi, I just received a Chroma Polaris from a seller online. Cosmetically its in great condition, I have installed the factory presets and it has a new membrane panel that is fully functional.

However, upon testing the synth it turns out the highest 3 black keys do not work when played, or cause infinitely sustained notes that requires turning the synth off/on again to reset.

Has anyone encountered this before and has any idea what the problem could be, and how to fix? I'm planning to get a quote from a tech but requires taking the synth into shop and waiting 7-10 business days for them to even look at it.

Any help appreciated, thanks.