None of the 8 analog phones on one of our RSTU3 cards in our school's Toshiba DK424 system will ring. Several phones rang for awhile (of the 8 total), including a couple new ones I put in couple weeks ago, but now those no longer ring either. I've swapped the card with another slot and associated phones, but those didn't ring either....so it appears the card is bad.

Before replacing the card, I want to make sure the new card does not meet the same fate. So I am wondering how to go about checking the phones to see if one of them may have a ringer short that may be pulling down the ring generator (?) in the RSTU3. Or should I be looking at something else.

Any ideas would be greatly appreciated.

Thanks and kindest regards, Bob