MEP004A Constant 200V

[DACollins]

Good morning all,
Please forgive my ignorance of the technicalities of these generators. I'm a basic mechanic, understand electricity (but sometimes slow to the 'ah ha'), and have no problem being told that I'm wrong.
That being said, this MEP004A ran very well until it didn't. I started it one day to use it as I had been, to power my welder, and found that the only voltage was around 200. Switching the output selector changed nothing, the previously functioning voltage adjustment knob did nothing. I could not find anything other than 5 fuzzy looking diodes on the VR board. (30554-72-2616)
I've searched and asked to no real avail about repairing or repair parts.
Advise?
Thanks in advance!

 

[Zed254]

Check out TM 9-6115-464-34 for cleaning and testing the voltage regulator.

TMs for the 004A here: https://www.steelsoldiers.com/threads/all-the-tms-you-need-to-work-on-the-mep-004a.155938/

 

[Guyfang]

Try writing a PM to: PEAPVP
He is a member here and repairs such things.

 

[DACollins]

I have the diodes removed from the board. I have some nsn #'s and part #'s.

nsn - 5961-00-981-6392 I found some info that says this nsn is no longer used, It crossed to
nsn-5961-00-811-8372 and 5961-00-156-0618

part # JAN1N3189

The number on the diode itself is- JX5614AXK or KK

Where is the best place to source these diodes?

I was on the WB website, but it seems difficult to obtain any pricing or order

Thanks in Advance
Doug

 

[Guyfang]

Are these things bad?

 

[Guyfang]

Mouser is a good place to get these kind of things. Also, the SS forum guy I referenced you to in message #3, would know where to get this stuff. He might even have them on hand.

 

[DACollins]

Are these things bad?

They looked discolored and had some white powdery stuff coming out of the ends. With the voltage issues, this was the most logical component to repair first.

 

[DACollins]

Well, we have good news and bad news. I put a couple of new batteries in the generator this afternoon and the engine fired up and ran flawlessly.
The bad news is, after putting 5 new diodes in the voltage regulator, I'm still in the same boat. Although slightly less than before, I now get a constant 176-179 volts everywhere. At the lugs, the convenience outlets, the volt meter in the panel, etc.
Additionally, I have no frequency adjustment or voltage adjustment by the panel. The output gauge also reads that the unit is producing 25% power.
I'm at a loss. I don't know where to look.
Any help would be greatly appreciated.

 

[Guyfang]

Well, we have good news and bad news. I put a couple of new batteries in the generator this afternoon and the engine fired up and ran flawlessly.

The bad news is, after putting 5 new diodes in the voltage regulator, I'm still in the same boat. Although slightly less than before, I now get a constant 176-179 volts everywhere. At the lugs, the convenience outlets, the volt meter in the panel, etc.

Additionally, I have no frequency adjustment or voltage adjustment by the panel. (You can not adjust the Hertz at the control panel, unless you have the precise power model. Only with the throttle cable. See if that works first.) The output gauge also reads that the unit is producing 25% power.

Try the proper hertz adjustment first, to see if any other problems go away.

I'm at a loss. I don't know where to look.
Any help would be greatly appreciated.

Open to see what I wrote.

 

[DACollins]

Open to see what I wrote.

I did in fact get the hertz adjusted via the throttle. It settled in around 60. I could at not get the voltage to change, other than if I sped the engine up, the voltage increased. I did (after shutting down) switch the voltage/phase switch to the left (416?) and the voltmeter registered around 300.

 

[Guyfang]

You can move the Volt/Amp selector switch, S8 while the set runs. Set it to the three phase position. Thats where you can test L1 to N, Then turn it farther to L2 to N and then to L3 to N. What are you getting?

 

[DACollins]

You can move the Volt/Amp selector switch, S8 while the set runs. Set it to the three phase position. Thats where you can test L1 to N, Then turn it farther to L2 to N and then to L3 to N. What are you getting?

180v regardless of s8 setting or lug.

 

[Guyfang]

All S8 does is test for voltages at different places. It will not change anything. So measuring at the lugs, brings nothing. When you set it to read L1 to N, and it reads 180 volts, you can not adjust the voltage with R1, the VAC adjust knob?

 

[DACollins]

All S8 does is test for voltages at different places. It will not change anything. So measuring at the lugs, brings nothing. When you set it to read L1 to N, and it reads 180 volts, you can not adjust the voltage with R1, the VAC adjust knob?

No

 

[DACollins]

The only thing I can change the voltage with is engine speed. That's a nominal change at best. Setting engine speed to produce 60Hz makes 180+/- volts everywhere, except the voltmeter on the dash. That reads 180+/-with the volt/amp gauge to the right or 300+/- on the left.

 

[Guyfang]

And that's the same at the lugs. L1 to N and L2 to N and L3 to N?

 

[DACollins]

And that's the same at the lugs. L1 to N and L2 to N and L3 to N?

Yes. All the same voltage at the lugs regardless of S8 setting.

 

[Guyfang]

Like I said before, S8 makes no difference. It only measures voltage, not changes it. It sounds like the volt regulator is not working. The R1, ACV rheostat looks good? Not burnt, or wires broken off? I wish you had access to a known good static exciter. That way we could exclude certain other things. There might be an exciter stator bobbin non op. Your getting voltage, but not enough.

 

[DACollins]

Nothing looks

Like I said before, S8 makes no difference. It only measures voltage, not changes it. It sounds like the volt regulator is not working. The R1, ACV rheostat looks good? Not burnt, or wires broken off? I wish you had access to a known good static exciter. That way we could exclude certain other things. There might be an exciter stator bobbin non op. Your getting voltage, but not enough.

Correct, nothing looks burnt, no wires off or broken. I don't have access to anything like an exciter bobbin other than what's on the machine.
My meter can check capacitance. I guess I should check that in the regulator?
I'll pull the regulator and check components individually as best as I can.
Thank you!

 

[DACollins]

As I understand some of these basic electronic testing procedures, I am going to have to remove the capacitors from the board to test them?
I also tested the new diodes and 3 of the 5 are not blocking current. I've also tested the three resistors on the board. I'll have to look for the values to verify they're within spec.
Could I have a short somewhere else that's causing or caused the voltage regulator to fail? I guess my question is more pointedly, where are the common failure points?

Thanks much!