My ISY can no longer see any Insteon devices (Z-wave is okay). I think the PLM may be to blame, though when I check "PLM Status" it says "Connected." The problem is there are no replacement PLMs available anywhere and in the meantime all my programs are non-functional (like half the lights in my house!)

I'm desperate for any help....

9 minutes ago, bcfromva said:

My ISY can no longer see any Insteon devices (Z-wave is okay). I think the PLM may be to blame, though when I check "PLM Status" it says "Connected." The problem is there are no replacement PLMs available anywhere and in the meantime all my programs are non-functional (like half the lights in my house!)

I'm desperate for any help....

What's your firmware and UI versions?

If you do a PLM link count how many links does it show?  About how many Insteon devices do you have?

Have you tried removing power from the PLM and ISY then powering up the PLM, wait about 15 seconds then power up the ISY

 

Everything just came back. I don't know why. I can see all my devices now.

Firmware: 5.0.16C (2020-1-25)

UI: 5.0.16C (2020-1-25)

PLM Link Count: 63

I did try unplugging both devices and then plugging back in, that did not work, but it's now working again. However, I am afraid it will go again at any time, as I have no idea what caused the first "outage".

Now would be a good time to do an ISY backup. How old is the PLM,  Is the led on the PLM on?

It could be that the capacitors in the PLM are starting to fail which can happen when the PLM is more than two years old.

The light is on and looks normal (no flickering and not dim). I’ve had the PLM since Feb 2020. 

63 Links sound low for most setups. You may what to try it a few times. As any activity may cause the count to be incorrect.

Did you power cycle the PLM?

Two of the signs the PLM has power supply issues.  Is a low link count and works for awhile after a power cycle. Though a 2020 purchase sounds like a awfully short time span. Can you see the Date Code and Hardware Versions on the back side of the PLM. That may also give you a clue.

I don’t have that many devices and I recently replaced a few with z-wave, though that has problems of its own. 
 

To be honest, I’m afraid to unplug it to look at the back as it may not come back up again!

You may want to do a show device link table test and then a compare to see if the devices link table matches what the ISY interface knows should be there.

I have not tried this myself. A member here bought a new 2413U USB PLM and then took the serial port board out of the old one and installed it into the 2413U. Then used it on their ISY interface fine. That would work as long as the old PLM didn't have a serial port board issue also.

Not a bad idea, thanks!