A series Melsec remote I/O Link problem

[yomp 0]

PLC CPU A1Scpu-S1

Remote I/O master card cards fitted Melsec I/O A1SJ51T64

 

Various remote I/O cards fitted for example: AJ55TB3-8D

 

Problem being experienced:

 

Parity error light flickering on master card

On reading the manuals this indicates to bad signals from a remote I/O card or electrical noise problems in the data cable.

No other error lights to indicate a particular remote card in question. Spurious signals to the main PLC come from various I/O cards, not any card in particular.

The weird bit is if we cool the master card using compressed air the parity light extinguishes and we have no issues.

 

Things tried so far:

 

Changed the master card but same issue.

Data cable from PLC to remote station (but not the daisy chains between the remote cards)

If the daisy chain was at fault We’d expect to see error lights on the Mastercard at the point of daisy chain failure.

Checked the voltages of data and incoming supply - both stable and correct.

There are 2 mastercards in total on one rack and another on an additional rack. One card has given issues for years but now a second card is doing the same on the same rack.

 

Other things to possibly try:

 

Change all the remote I/O cards associated with one Mastercard initially but not sure if we have enough of this old gear in stock to do so.

Change the daisy chains

Change the main plc backboard.

Manual attached.

Any help or similar experienced would be greatly appreciated.

manual_IB(NA)-66574 (2).pdf