My EISY has lost contact with all of my Insteon Devices. I have been operating normally with eisy/insteon for a year or two, but now, the eisy cannot effectively communicate with any of my insteon devices.

I am using a 2413S PLM (Address 2B.93.EB)

The PLM is attached to the eisy via a Serial-USB cable.

The PLM Info/Status comes back with , "3B.93.EB /Connected." When I do the PLM diagnostic for PLM, the system goes through and extensive set of pop-ups where it seems to be doing a "Restore Modem (PLM) procedure.

After completing the pop-up sequence I can send commands from the Admin Console t turn things On and Off, but the device does not actually respond.

Some devices show the device turning on and off (without actually responding). Other devices get a pop-up saying "Cannot Communicate with [deviuce name]. Please check connections." The device then gets a red exclamation point on the Admin Console Main list.

I have another 2413S PLM (Address 3D.95.E3). What is the procedure for swapping it in while doing the least damage to may rather extensive system?

My initial gut feeling is that the PLM has gone bad. Thankfully you have a spare on hand. If it's a used PLM, do a factory reset on it first (plug it in while holding the link button pressed until it beeps). The proper procedure for replacing it is to start with making a backup. Then:

Power off your eisy

Replace the PLM with the new one

Power up your eisy

Log into admin console and under File -> Restore PLM

This will take time, since it will be writing out the new PLM's address to every device. Then if you have any battery powered devices, these will need to be restored individually (Restore Device) by waking them up by pressing their link button and initiating the restore.