PF 755 Active, Motor Won't Turn

I got a call yesterday from a plant that I support. They had a powerflex 755 vfd that from what myself and the other controls engineer can tell over the phone has gone bad. The plant did not have a HIM so the data I have is limited.

The motor runs fine with the drive bypassed and run direct to the 140M starter. The drive does not trip a fault or alarm. Control is via embedded ethernet/ip. By observing changes of the STS indicator the drive appears to respond to start, stop, and resets via ethernet. The drive hardware enable feature also responds appropriately and there is 24VDC on the di0 and a 0vdc on diC.

When the drive shows active the heatsink fans come on appropriately and there is 54VAC present at the output terminals, as read by a Fluke 117. During this state the rotor can be turned by hand. This condition also occurs on a different motor that we tried. We also moved the speed set point up and down the full range the machine will support (0hz-100hz) and observed no voltage change at the terminals. I know this reading may not be valid without the appropriate meter, but I would expect some change.

This drive ran fine for about 3 months and did not die under a load. The maintenance man on the phone said that they shut the machine down for weekly TPM and cleaning after which the machine would not start.

I find it odd that not only does the drive not fault at all, but it has voltage output as well. Most of the time when a VFD dies around here it won't come on at all or has a recurring fault of some type. Has anyone seen anything like this?

Is there a hardwire enable?

I would take the drive back to keypad control for start/stop and speed and see if it will run the motor that way. If yes, than the drive is probably ok but something is wrong with the communications. If no, the drive is probably damaged.

I had a PF755 drive that was indicating that it was running but is was not supplying any current, it turned out to be the power interface board.

Alan.

Yes there is a hardware enable. I had maintenance check that there was a good 0vdc reference and 24vdc signal at the terminal. I cannot have them put he drive in local because they don't have a HIM. The drive status indicators are changing appropriately with commands from communications. Of course I'm not sure it is getting a good reference buy I find it hard to believe that it would get start, stop, and reset but lose the reference.

The power interface board may be the issue, I probably won't bs sure until AB gets ahold of it.