A redundant CPU(picture PLC-118), master PLC which having EXTF(picture PLC-118-B-OVR) but standby PLC no error. This shows that the X5 network is working fine.

However master PLC having EXTF and could not identify the root cause. Because the Diagnostic Buffer which has maximum 3200 entries have overrun by the errors which not related to the cause of the EXTF.

After checking on the Hardware Configuration, the master PLC rack shows there's missing sync module 2(picture PLC-118-B). But both PLCS are running normally and both Link 1 and Link 2 at the hardware both having constant green LED.

LED IFM1F, IFM2F and REDF no trigger.