MEP-803a - Field Flash Grinding Noise

Guyfang said:

That's the reason R14 is there. To lower the voltage/amperage. 8.5 volts sounds about right. So, if you have 8.5 volts on the A1-F+, and no volts or hertz reading, we need to maybe look into the TM to find the procedure to test the Excitor circuits. Because 8.5 volts is way more then is needed to light off the main gen.

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Ok, thank you. I will get on this and hopefully get it figured out.

Skip to page 213, (PDF reader) yes, you can remove the end cover. Just don't forget to take the Neg cable off, because if someone bumped the starter, big damage is possible.

Amazing watching/reading as Steelsoldiers help another out of a jam with hard earned knowledge and expertise! You guy ROCK!

(YES, "Guy pun" was intended......lol

Well I went through the TM and it appears the exciter rotor and rectifiers need replacement. I really appreciate Guyfang assisting me in troubleshooting this problem. I have messed around with 802/803 generators for a few years and this has been a great learning experience for me. Now it's time to find the parts...

hcso2332 said:

Well I went through the TM and it appears the exciter rotor and rectifiers need replacement. I really appreciate Guyfang assisting me in troubleshooting this problem. I have messed around with 802/803 generators for a few years and this has been a great learning experience for me. Now it's time to find the parts...

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Are you looking for a complete altenator or just the parts causing problems?

USAMilRet said:

Are you looking for a complete altenator or just the parts causing problems?

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I am going to test the generator rotor tomorrow. Hopefully it checks out and I only need the exciter rotor (201-3466) and rectifiers (358-0070 & 358-0069)

hcso2332 said:

I am going to test the generator rotor tomorrow. Hopefully it checks out and I only need the exciter rotor (201-3466) and rectifiers (358-0070 & 358-0069)

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Did you use a known good meter for the measurements? I have found that an analog multimeter will show results differently than a digital meter. We are talking fractions of an ohm here to just a couple of ohms. Just enough to tickle the needle that is below the threshold of some mid to low end meters. I have always relied on a good analog meter for testing. I ask because I just tested one of my MEP803A units prior to initial startup. It was sold as scrap metal so I had to check everything before I started the unit so I am very familiar with the test you needed to do. Exact place in the -24.

It is also better to disconnect (isolate) the alternator from some of the test. You should disconnect every terminal on TB5. The wires are marked T1 thru T12 so you don't even have to tag them.

Good luck. I don't know about parts needs availability. From what I understand common parts disappear fast. Heavier and electrical not so much.

USAMilRet said:

Did you use a known good meter for the measurements? I have found that an analog multimeter will show results differently than a digital meter. We are talking fractions of an ohm here to just a couple of ohms. Just enough to tickle the needle that is below the threshold of some mid to low end meters. I have always relied on a good analog meter for testing. I ask because I just tested one of my MEP803A units prior to initial startup. It was sold as scrap metal so I had to check everything before I started the unit so I am very familiar with the test you needed to do. Exact place in the -24.

It is also better to disconnect (isolate) the alternator from some of the test. You should disconnect every terminal on TB5. The wires are marked T1 thru T12 so you don't even have to tag them.

Good luck. I don't know about parts needs availability. From what I understand common parts disappear fast. Heavier and electrical not so much.

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Thanks for the heads up. I am using a Fluke 77 for testing. The exciter stator was good at 11 ohms. Th exciter rotor leads I got .5 on all leads. I couldn't get any readings measuring the rectifiers. When testing the exciter rotor I was getting a reading from both F1+ and F2 with the rotor shaft which the TM says should show no readings.

Just take your time and follow the book. Measure everything twice, if not three times. Can't hurt, and might save you big time money. I think Light in the Dark, and a few others here might be able to help with some of your parts needs.

I wanted to break the tests down a bit last night, but the Crown Prince, (my new Grandson) made an appearance here, and everything came to a standstill. Mother, Grandmother, Great Grandmother and the cleaning lady turned the house up side down. All I could do is hide in a corner. I can't walk right now, and all these silly lady's running around, made crutches even more dangerous. I am going to kiss the ground and burn my crutches when I can walk at last!

Good news, I ordered a new exciter and installed it today. Everything works great now, still have to load test but she's producing power! Wasn't too bad of a job swapping it out. Thanks again to Guyfang for helping me troubleshoot this problem.

Any time partner! Lots of others jumped in here also. Don't forget to thank yourself, you did all the work!

Well I am back. Started out on the generator to do a load test today, but started having issues.

First, whenever I start the generator it never automatically excites, I have to make sure to hold the start. When this happens the frequency meter jumps to 65 then to zero then stabilizes at 60 hertz. This doesn't happen on my other generators?

The generator then produces power but it slowly fades. At 120/240 the AC Volts Meter goes to 240 but slowly creeps down, sometimes all the way to 180. The potentiometer (R1) has no effect when adjusting. I went through the TM and the A1 checks good, I also replaced with a known working A1 and the generator does the same thing with the voltage fading.

Now the scary part, I am smelling a burning type smell. I can't place where the smell is coming from. Possibly the generator head/exciter area. The only possible thing I can think of is I forgot to tag the F1 / F2 wires going to the exciter on removal. When replacing the exciter I believe I put them on the rectifiers the right way.

Any ideas?

Do not think you know. Make SURE you know. Also check the A1. and the F1 and F2.

Guyfang said:

Do not think you know. Make SURE you know. Also check the A1. and the F1 and F2.

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Is there a way to identify F1/F2 wires from the rotor to the exciter? Neither of the wires are marked.