[cctalk] Papertape-Reader Decitek 442A9: need manual/schematics

I have a Decitek 442A9 papertape reader which needs repair. I have already replaced the belt, but that is not enough. The reader behaves very strangely. It starts running as soon as I apply power. And there is another problem: when I load a tape, it rattles irregular during reading. This is not a mechanical problem, it seems to react to the pulse of the feed hole, which arrives at the wrong time. I'm pretty sure, that I have to adjust the sprockets somehow relative to the stop positions of the stepper motor. It was nothing to be found online except pictures of a similar model 443A9 at RICM: https://www.ricomputermuseum.org/collections-gallery/equipment/dec-pdp-8s-4. The controller board number is 30291A Does anyone happen to have the manual and/or schematics or any other documents? Thank you, Micha