Control.com - Nerds in Control

We received DROP#93 "MK5 common I/O communication loss" alarm appeared for 1 second and cancelled by itself for Simplex Mark-V control system with I station. The GT was not tripped and nothing happened. Can anyone help me what to do to get the cause of this alarm and what is the meaning of it? What is the source of this alarm?

I/O Communication loss is normally caused by a loose or weak connection if it blinks in/out as you described. There is the possiblility of a failing card. You can diagnose this more using the maintenance manual GEH-5980. The unit will not normally trip unless you loose your protective core. Check your processor status and you should have A7 display. A0 to 3 will indicate a card failure. Hope this helps.

Becerrra is mostly correct. I would add that one of the potential causes for loss of communication (after a long period since installation when no comm problems were experienced) might be the corrosion being experienced by many on the cable and connector pins and contacts. It's always a good idea, during a maintenance outage, to properly power down the control system, and then at a minimum disconnect or unplug every single cable and connector several times, one at a time, looking for any corrosion (usually white powdery substance). Also, if you haven't done so already, use a conductive grease on the connectors before reconnecting them. (You can usually find tubes of conductive grease and instructions in the boxes of spare printed circuit cards.) Unseating and reseating the connectors can help to prevent and remove corrosion. It's just part of what should be normal maintenance for all control systems in industrial environments.

I would also add that if you are experiencing other Diag. Alarms, especially Contact Input Failures, along with battery ground alarms, that this would also be a good time to investigate and resolve any grounds (remember, if grounds have existed for a long time, it's a safe bet there is more than one!) and check for any induced AC voltages on the contact input wiring or ripple from the battery charger output. (This would need to be done with power on the panel.) Too many Contact Input Failure, and on TMR panels intermittent Voting Mismatch Diag. Alarms, can cause communication "interruptions."