The ring generator is built on the RSTU analog card if I am not mistaken.
I would try another RSTU card, it is possible something has damaged all 5 of them. Or pull the cards out, reseat them and push the white buttons on the power supplies that have the RSTU cards in those cabinets.
If you have a friendly tech, try one of those RSTU cards in a system that tech has.
I always put a 1/1,000,000,000th of a second surge protector on a system as the cheap surge protectors would let cards get fried and while some Toshiba cards may not fry, others could.
