Since I'll be out most of the day and I have time now, here's some things to look at if the controller switches you mentioned are the RCS LED or LCD keypads connected to the RS485 port. They could either be daisy chained directly to the C30 or connected to an RCS 8 channel RS485 Hub which is connected to the RS485 screw terminals on the CS30 main board (the CS308 has the hub onboard).
Since (I assume) none of the keypads are working, I'd first check power to the hub if you use one - could be as simple (hopefully!) as a burnt out wall wart. For each device connected to the hub an LED on the board should be lit. Check all the wiring to see if any leads are broken. The next test would be to connect one keypad directly to the RS485 screw terminals on the C30 main board. If it works then the hub would be suspect.
If it doesn't, then the Maxim RS485 chip on the C30 has likely failed. I've had both Maxim RS232 chips fail over the years and replaced them. Fortunately, the RS232 chips are socketed making replacement easy. UNfortunately, the RS485 chip is soldered to the board (on mine anyway) located almost adjacent to the RS485 terminals. It's an 8 pin through-hole chip which means that it's not difficult to remove if you're comfortable with a soldering iron and desoldering braid. You'd then solder in a chip socket and plug the chip into it for easy future replacement. The worst part of the job is disconnecting everything from the CS30 to remove the board from the case. I had to do exactly the same thing with the opto-isolator chip on the IVR board years ago.
If the chip needs to be replaced, Jameco.com has them and the socket for about 3 bucks plus shipping plus a $10 fee if your order is under $20 but it's easy to find a few more things you "need" to meet the minimum. If you're not in a hurry you can buy 10 chips for about 3 bucks from China on eBay and wait a few weeks.
Of course, if I guessed wrong about you referring to RCS keypads this is all moot and we can start from the top.