Telemecanique Digital output problem

Hi all
I have just encountered a problem with an output on a Telemecanique TSX 10740 (4740). On my first slave rack the last card (TSXDST 24 82 24 bit 24V PNP digital output)decided to keep the 23 o/p permanently on without the indicator and being shown off on the process image on the pc. I exchanged the card for a new one only to find that this card does not turn on the 24 o/p although this is shown on in the pc, also the led for indicating the 23 o/p status does not come on although the 23 o/p operates normally.
I have performed all the normal checks for bad connections etc. but do not want to start swapping other cards around from other parts of the rack because the machine is still able to run.
Has anyone ever encountered a similar problem with this type of plc or have any ideas. The PLC is of 1993 vintage and is now obsolete, it is however quite an extensive system and I require further service from it.
I look forward to your replies.

Thanks all.

I don't know about this particular PLC, but I have seen this type of problem on other brands at least twice.

Once was a bad rack, the other time was a defective Remote I/O processor card. Of course you also might have one bad module which is causing a good module to look like it is defective.

All I can suggst is to keep swapping all modules in the rack with known good ones.