I'd try taking it apart again, as you did for the original error - or further, any other easy to release and replace units.
Then put it back together again and see what happens.
The laser printers I've seen tend to have quite a few spring loaded connections between different parts, and it could just be a slightly tarnished contact somewhere, which may be fixed by removing and replacing whichever part is involved.
If that does nothing & you are considering it as junk - pick it up an inch or so and drop it on a hard surface!
Again, the idea is to rattle any electrical connections, but without enough force to damage the optics or mechanics..