Rotary encoder on Unimat PC CNC


I am trying to get a Emco Unimat CNC working. However, the rotary encoder does not seem to work. As I understand it is an optical sensor, and I measured it and it gets 5 volt from the controller card. However there is no visible light from the unit/sensor when connected and powered.

Maybe a dumb question but should the light be clearly visible?

The sensor seems to be roughly the same as on the 5CNC, photos of the sensor is available here:

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