Philips DCC 170: Works fine, but motor spins too fast

My Philips DCC 170 which worked fine nicely recently “got stuck” during playback making only a squealing. Upon opening I found the fairly new belt rather slack already and replaced it. After closing everything up again, the player now seemingly works fine and reacts on button presses correctly, but the motor spins way too fast. The device correctly “thinks” its in playback, rewind, forward, or skipping and displays information accordingly, but due to the high speed it will emit only intermittent spurts of music and time information.

I opened it up twice, so it likely won’t be any of the critical solder joints. Still no dice.

Anyone have an idea what might be at fault here?