STOP ! the Evil Servo
(LOVE that picture BTW) is easily tested in the car , it's easiest if you source the electric plugs from a junker but you can also make up some test leads with crimped on ends .
DO NOT even *think* of taking anything apart further than you need to , this is how you'll wind up chasing your tail forever
You can use battery voltage to run the servo back and forth , remember : it
must stop moving with a thunk sound , not slowly load down until it stops moving ! .
I'm in the middle of a serious shytestorm @ work but I will write you a how to test in due time if you need it , it's pretty simple , IIRC George has a nifty booklet he'll snailmail you for free .
yes , I have good used amps but don't buy one until you _know_ the servo is 100 % O.K. ! .