Plug n play command control culvert unloader problem!

  First you have to comfirm the ir emitter works (common terms in a light detection circuit is "emitter"& "receiver"). You can most often see the IR emitter light up with a digital camera; the easiest test. The receiver side will either pass voltage, or block it as it's pad is saturated, then sending that signal to an ic or transistor. And here is where I'll say I don't know the board so dont want to go further without saying so, but I never had a warning or issue with checking an IR reciever by a volt meter. My E/R work was with many different counters and motion detectors which all had great design for the most part (lots of isolation)

  On occasion an ir led may go bad and put out a frequency the receiver can't actually see, but a camera still might, I kept extra leds ran off batteries for quick testing that rarity before finally condemning the reciever or moving up the ladder of parts that were related. I also had to balance my pay rate against a handful of cheap parts being quickly swapped out. Good or bad parts didn't always matter. Indiscriminate swapping of a grouping was often cheaper than paying myself to hunt a specific issue because some things needed to be unsoldered to test anyhow. You arent being paid, but there is still a cost/time balance unless it's more about just learning.

 Follow the traces and check each part, usually the closest switching componant is the issue if the Emitter/Receiver is ok. Transistor, IC, etc. Oh, look for an opto isolator too, after E/R check, start trace hunts there. Burnt led? Check its resistor and any related diodes too, or you may burn the replacement on power up.

The E/R testing should give you a head start on a fix till someone more familiar with it jumps in to go deeper. If they don't, hunt common parts to test via traces. (following house light traces might help find a common ic, etc.. hunt with your logic)

(IC? A "chip"; an Integrated Circuit; a grouping of various componants/functions slapped into one small package)