This sounds like the stepper motor is failing with heat. Given the Hz signal is straight from the alternator.... a loss of the signal would intially cause the unit to overspeed. (Wiring from alternator to control board problem maybe... also heat related) * Measure resistance across any combination of orange, yellow, brown, or black should read approximately 20 OHMS. * Measure from red to any other lead should read 10 OHMS.
The only thing that made sense to me is a problem in the 10 Ohm freq sensors or the stepper motor.
Noting you have changed the control board and your still having overspeeds Look at the the Hz sense portion. I would bet your shutdonws are being initiated due to over-voltage vs over-speed. That you may have to sort out.
Sounds like a long day... of troubleshooting. 5 - 6 hours wait and then PANIC just to duplicate it!
Hopefully you have the service manual. I have the one for the 15Kw and Up.. but sense circuitry is pretty much the same.
Sense circuit...
* Testing from any lead to stepper motor case should read INFINITY.
Orange or black to Black or green One leg... 20 Ohms
Yellow or Red to Brown or white 2nd leg 20 Ohms
Again Stepper motor or sense wiring / windings... is where I think the problem lies.
Good luck and I am willing to keep taking stabs at this. 40 years as an electrican here.
Thanks for choosing FixYa,
Kelly
I wanted to add a couple of experiences I had over the last 4 decades. Two in particular.
- I had a unit that would overspeed at random only in the winter time. After weeks of back and forth I FINALLY fgured out that when their furnace kicked on the unit would speed up because it was leaning out. i.e the furnace and the generator were on the same gas line and the furnace would drop the NG pressure so the Generator would lean out. (Talk about heartaches!)
- One other unit... It also would overspeed and shut down. The main line gas presure was to low because the regulator by the meter was stuck in a fixed position so anytime there was other than nominal gas usage the generator would lean out. This one was associated with meal times. When they started using their gas range and the generator was running it would speed up and often trip off.
Just passing on some food for thought if you run out of other viable options. I would still concentrate on the sense circuit for now and possibly even rewire the sense circuit and do MEGGER checks looking for stray grounds when the unit was HOT.
I do wish you the best.
Kelly
If you need a service manual I think I can find a PDF copy for you on line that you could download.(Free!) I would appreciate having the model number so I can get the correct manual link for you.
Kelly
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