Lightening is forever frying Versatilities.  The line cards fail for a past time.

You could try swapping the black PSTN modules for new, but to be honest, with a fried system, you are best swapping the CCU and the modules.  Faults will likely start to appear over time otherwise.

For the price of a second user system with cards, it is worth swapping the lot (although the black PSTN cards can be more expensive than the red ISDN ones).  Beware of ones on Ebay - They are often ones which have been hit by lightening, and show no immediate issues, but will fail in time.