My PowerMate was always unreliable. The *#&* driver sucks because it stops working after hibernate and resume. As you can imagine, having no volume control much of the time is no good. To recover, only a reboot helps. Unplugging and replugging of the PowerMate won't do it.
I messed with devcon but gave up because it lists a million devices and I couldn't figure out which one of them was the PowerMate.
I wanted another solution that works with the mouse wheel and software like volumouse.
I took an old Kensington mouse. It turned out that the rotary encoder of the PowerMate is compatible with the controller of the Kensington mouse. Three pins: ground and two signals.
I unsoldered the original controller from the PowerMate. I wired the rotary encoder to the Kensington controller with one half of the original PowerMate cable. I wired the other half of the PowerMate cable to the USB side of the Kensington controller. I also wired the push-switch to mouse button three.
It works, using volumouse I got volume control on mouse wheel with my modified PowerMate.
If you try to repeat this, be sure to use a mouse that uses a three pin, electrical rotary encoder as opposed to an optical one.
Spray painted PowerMate with mouse controller:
PowerMate controller is removed and the rotary encoder wired using the original cable:
The leftovers. The PowerMate controller is the disk shaped board: