Thank you both for your replies.
Firstly, the card is a WF723A, so it seems the replacement would be the FM 453.
The drive is giving the error "following error at standstill". We have changed the encoder and the encoder cable, and this hasnt solved the problem. We have checked the motor and gearbox, and they seem OK. Only one drive is giving a problem, all the other drives are OK. The error seems to only happen right near the end of positioning (for example, the last 10mm). What I cannot understand is that the PLC program has been written to ignore and reset this error - but then the machine will cut the wrong size
I have downloaded DriveMonitor to see if I can identify the problem, but I cannot get my laptop to talk to any of the Masterdrive MC drives