Serial ports stopped working - power supply issue!

Just posting this as an FYI in case anyone else experiences the weirdness I've just gone through!

We have a system that's been in place for close to a year with no problems.

Then yesterday two of the serial ports stopped working (this is on a 3101-SIG), although one other still worked ok. All other IP based comms was also working including comms to the panels.

Engineer was dispatched where we also found out that relays weren't working either. We swapped out the controller but exactly the same issues became apparent.

The engineer then had a light-bulb moment and swapped out the power supply and every thing sprang back into life.

Turns out the psu was only putting out 5v instead of 12v. Enough to get the controller working and supporting IP comms but not enough juice to power the serial ports or relays.

So - another item to add to your check list if you experience something like this.