As readers of this blog know, a few months ago I got an open circuit indication on my Airmaster prop controller and it turned out to be a broken wire in the carbon brush assembly (a few hours of work, but not too difficult to replace). More recently, I got another open circuit indication and assumed that I had another broken wire (though it would seem strange that it would happen twice in a few months on a low-time airplane). A couple hours of work to disassemble the assembly and check it out and that was fine.

 
Further debugging and it looked like the pitch motor itself had failed. Voltage applied directly to the motor did not move the motor at all.

 
Turns out that the motors in Airmaster props older than a year (give or take) have a design prone to open circuit failures. So much so that they completely redesigned the motor and there are formal instructions for replacing the motor. The new motor is more robust and faster in changing the pitch too.

 
My new pitch motor arrives on Wednesday (thankfully covered under warranty). I'll have to update the controller parameters with this change and I've already got that file. I'll also update the controller firmware while I'm at it.

Photos show the disassembly of the hub to remove the pitch motor itself, which I'm holding in the last photo.