Yeah, I spent ages troubleshooting that one. Everything worked on the control system except for the IR input on the X850B... I was about to give up and resort to using an IR eye (which doesn't look great on these units), when I must have plugged in the cable "incorrectly", and suddenly everything worked - at least for a minute.

Eventually I realized that if I didn't push the cable in to the final stop, everything worked fine... but as soon as that last click was heard, death. The jack was firm enough to hold the cable correctly at this "1/16th away from the end" position, and it's been working fine for 10 months.