I sent this as a response to PM, but thought it could be useful to someone in the future, so I'm posting it here also.
In switch test, there is a dot that corresponds to each switch. You can see in my video, there is one that is displayed when I block the loop with my finger. If that dot is always displayed, the loop is always triggered. If it's never displayed, it's not being triggered at all.
You won't hear any audio unless you turn it on using the enter button. So, I guess it's not clear which case you have. I would guess always triggered, as if a ball is always there.
That could be caused by either the emitter or receiver. As Ben mentioned, if your door opto works, it's much less likely that the emitter is the problem. Both emitters are on the same board and share a power source. It's still possible you could have a failed solder joint on the ghost emitter, though.
The emitter is always on if the game is on. In my video, you can see it come on a soon as I power the machine on.