Stepper motor for Generac 990, Portable generator, 17.5 kw

[staninlowerAL]

I'm looking for tips and information on replacing the speed controller for my 19 y/o Generac generator, OEM part number OD4522. This is my first attempt on any repair so any comments are welcome. Stan

 

[staninlowerAL]

Update, Got a copy of the service manual online and was able to check the stepper motor, checked out OK. Replaced the idle speed board and made some adjustments. Unit is performing Ok for now. Maybe need to fine tune the voltage output when I locate the spec sheet in the manual. Stan

 

[staninlowerAL]

2nd update: Looks like this project can be marked complete. Glad that it seems to be doing its job, once I understood that the engine rpm is controlled by the output of the generator it was a simple repair to replace the idle speed control circuit board. There is no mechanical governor to regulate the engine rpm. The picts are a shop built test device with plug in voltage meters. Hope this helps someone.