Just a little feature on the Power Valve Servo. These things, in my experience are prone to failure. The one featured here has three faults which I have encountered more than once, on several Servos. They are burnt out circuit boards, broken gears and springs missing from the carbon brushes. Here's a quick quide to dismantling.
Remove the magnet canister that covers the motor. This has 3 screws and may take a bit of effort to get off, there is a gasket sealing it on, and the force of the magnets is quite strong.
Remove the back cover to expose the circuit board, here you can see it is burnt. Seperate the plug connector, and undo the two screws.
With the board removed, the gears are now visible. Again, you can see a couple of teeth missing from the large gear next to the motor drive gear, the one on the left. Lift out the large gear, and its spacer.
Push the black plastic fitting into the casing to get the motor winding out. Its a snug fit, so take care not to damage the motor.
With the motor winding out of the way, more damage can be seen.
The motor winding looks like this, note that this one is in poor condition.
All that remains is to use an adjustable spanner and allen key, and the pulley can be removed from the casing, which can now be cleaned up and rebuilt/tested or binned if its as bad as this one!