pingu.freak@web.de writes:
> The hardware is 5 years old... It was not possible to get new hardware
> for this project. :/
Disassembling and cleaning the machine has worked for me in similar
cases. You'd be amazed how much dust can build up on a circuit board
... and if the dust is even a little bit conductive, it can be the cause
of misbehavior.
regards, tom lane