How to check if filament sensor is ok? The filament sensor of my i3 MK3 stopped working. In the support menu, it just says IR: N/A. This is the same output as if I disconnect the filament sensor.

My PCB says rev 0.2e and this is what I see:



In the Prusa Shop, I found a laser sensor, which has 4 pins, so that's probably what I have.



I have already checked the voltage coming from the Einsy cable. It's 5.02 V, which is probably ok. The remaining two pins seem to be SCL and SDA, so it's likely a I²C bus.

I have Arduinos, ESP8266 and ESP32 around. Is there a test routine that I could run on the filament sensor, other than Prusa's N/A display?
You could try out this Arduino sketch and see if the Arduino can find the sensor on the bus, but I'm fairly certain that the chip has developed a fault and stopped responding to I²C commands, hence the error, or it's giving a value that's outside the limits set in the firmware. 

I'd also recommend getting in touch with Prusa Research, they have very good support and can tell you what part you need for your machine.