I will trouble shoot with a blink emitter, test emitter or digital camera(cell camera works too) will look for a blink/flash at the device...usually first thing I check when a device wont respond.

I havent had any RP units lose a port yet but have had an occasional emitter not work...usually due to wrong polarity wiring, pinched in a case(we try to bury emitters inside) or neglect on installation....pulled to tight and broke a wire.

I have only had a few bad out of the box emitters in 15 or so years