Here's an important note about why the PGM's blow.

Mostly the problem is related to the RC valves being dirty or too tightly adjusted, but I have just found that it can also be linked to a dodgy TPS.

A fractured wire obviously causing strange resistance readings killed the RC valve operation on a PGMIII. A new TPS solved the problem.

If you have PGM's blowing up and non moving servos check out the TPS.