Thank you for all your help. I've learned a lot in one post!

The theatre tries to raise money for many things so it is a matter of priorities. They have no idea if it's repairable or have to replace the whole thing for $1000s of dollars so I think it helps that I've found that we're looking at just a card to replacement or repair. I think everyone has been assuming it would be really expensive to repair or replace.

To answer some questions:

► We could definitely get away with 9 lines or less.
► All tone lines.
► Depending on the phone location, there is a light or buzzer with each handset for a 'ringer'.
► Lightbooth, stage, lobby, dressing rooms are the phone locations and cast, director, stagehand uses the phones. Used for communication before and during show to keep things running smoothly. During the show, communication can be critical to fix problems on stage.
► Would be interested in upgrading to a newer system if people have suggestions to something that would be more reliable in long run.
► I think the handsets attached to the walls are still necessary, whether they are wired to the base station or wirelessly connected is another issue. We just don't want the handsets to wander off from key locations.
► I can do simple wiring (and follow instructions) so I could install another system if it was on par with the current Melco. I think I would need a couple more tools to do the wiring to the backplane or make any special connections.

I didn't realize that there was supposed to be a fuse at the 10VAC 3A terminals. (That would explain why there is a gap there!) And that must be what is connecting the terminals between the 24DVC 2A terminals. I'm not familiar with that fuse type, but I assume the person who set this up, couldn't find the right terminal-to-terminal fuse type. Do they still make these? What are they called?

Apologies that not shown in the original picture is that I had disconnected the 10V 3A wires on the power unit that were connected the Aud Grd/Aud Sup terminals on the backplane. (You can actually see the other end of the wires on the right of the original picture.) I've drawn in the disconnected wires:

[Linked Image from i1156.photobucket.com]

@Arthur - Are the units wired correctly, knowing that the 10V 3A is separately connected to the Aud Grd/Sup terminals?

Thank you again for everyone's help!