I was just using an LBX yesterday and I have to say that it sounds like you have everything right. Should be working, should at least see in the "output" display the intensities changing regardless of what the lights are actually doing.
In the "output" display it should show you enough info to see what is/is-not going on.
If what you say is true, that there are a few subs not working and such, than perhaps yes a key, keys, or
fader, or even other part of the 'effects' portion of the
console is not operational. A repair may be in order.
The LBX may be an aging
console, but it still works just fine and gets the job done very well in most circumstances. The only problem with the one I was just using is that the disk drive did not want to work (a major pain as it was for a drama festival, I was
house tech, and had to manually jot down all cues/subs). It was rented too, so I am kinda pissed with the rental company there.
Anyways I'm sure you can still get it repaired if you so desire.