got a throttle problem it keep revving up and down, the machine is a EX 200 LC Hitachi, ser. no 14C-83995
replaced the stepper motor it ran ok then it started fluctuateing RPM, and can not adjust the throttle at all with the control pad could it be the sensor next to the stepper motor ? or shoud i start some where else ?
14C sn prefix indicates machine is EX200LC-3. New problem to you or has it been ongoing ? Check the EC control sensor resistance, see screenshot below. With harness connected, using a voltmeter back probe terminals #2 and #3 and check the EC control sensor output voltage. At Idle speed setting should be approx 2.5 volts , high idle setting should be approx 4.5 volts. Sounds like the engine speed control buttons are ineffective, so turn the EC control sensor by hand and check that the voltage changes. .
I will give that a try might need a more acurate meter for this kind if work, imine is kind of cheap thanks Dan