MEP803A - Diagnosing a Voltage Regulator

[scjarena]

I have a MEP803A, 400 hrs. Its always worked good for me until few couple days ago, the voltage is low, erratic, and the voltage potentiometer knob doesn't affect it. Now when I start it again the frequency needle it jumping back and forth erratically. It has the fuse mod on the regulator, but not the varistor. I've looked thru the manuals and I'm having trouble finding a detailed method for testing the regulator. Any help would be appreciated.

Thanks
Mark

 

[kloppk]

The test procedure is in the -24 TM for the generator.
TM link ---> 803 TMs

 

[Light in the Dark]

I have a MEP803A, 400 hrs. Its always worked good for me until few couple days ago, the voltage is low, erratic, and the voltage potentiometer knob doesn't affect it. Now when I start it again the frequency needle it jumping back and forth erratically. It has the fuse mod on the regulator, but not the varistor. I've looked thru the manuals and I'm having trouble finding a detailed method for testing the regulator. Any help would be appreciated.

Thanks
Mark

Are you going by measurements, or gauges, with your descriptions above? Is the engine speed changing as you notice the hertz changing?

 

[scjarena]

Are you going by measurements, or gauges, with your descriptions above? Is the engine speed changing as you notice the hertz changing?

Engine is running at a smooth constant speed. I was going by the gauges on the panel. I didn't use an external voltmeter.

 

[scjarena]

I went thru the tests for the voltage regulator in the -24 technical manual. The regulator passed the several voltage and resistance tests. When I run the unit, the frequency is staying steady for the most part at 60hz. The voltage is what varies consistently, like riding a sine wave. The voltage measured at the output terminals show this, which reflects the pulsing. Also I when I connect to my shop lighting and run the unit the lights fluctuate between dim and bright. All this is with the engine running smooth and steady.

Not sure where to go next. I see a test for the AM-VM transfer switch in the manual, whatever that is. Any ideas?

 

[kloppk]

With the AC voltage fluctuating like that I say the VR is indeed bad.

If your shop light is doing that there's no need to test the AM-VM switch.