GR3750 elevator reversed

[cokwax]

The sensing of the lower limit sensor has changed. The elevator paper feed tray now lowers when I close the light path of the the lower limit sensor. Once opened, the tray stops moving.
I have tried several sensors with the same result. I also changed the MOTOR PCB in vain. What is the probable cause of this?
Actually, I have even done a sensor/SW test and the result is the reverse. When the sensor is open, It sounds at 0.1second interval and when I close the sensor, It sounds at 0.5s interval.

[Iowatech]

Has there been anything that has recently disturbed the local power utility there, like energetic storms or nearby construction? If so, there could have been a power surge that put bad data in the machine's working memory. During the time the GR line wasn't obsolete, I observed power surges causing those machines to display all manner of undesirable operation.
If that's the case, try the memory resets.
Could also be the main board, it has a hand in every machine operation. If the resets don't work, the main board would be the most likely suspect.

[cokwax]

Thanks for your reply.
Actually, I realised the cause: The technician I had called to help me service the machine had put a new sensor which was not similar to the original. The sensors we kept on changing were all the same. I removed one original sensor from the pressure disk used it as the lower limit sensor for testing purposes and the elevator worked normally. I will now look for the original sensor to replace.