MEP 002A Unstable Voltage Then No Voltage

For the past 2 years a friend has owned a MEP 002A with unstable output voltage. It was like that when he bought it.

The reconnect switch has always been in the 120/240 single phase position. When started the output sometimes is 120/240 and sometimes it is 155/310. During a typical 30 minute run the voltage will jump between these two amounts 2-6 different times. The voltage adjust pot will adjust the voltage +/- 20 volts or so when the voltage is 120/240 and even when it is 155/310.

He asked if I would look at it. Like a fool I said OK. We loaded the 002A on a trailer and towed it about 10 miles to my house. Two of those miles were over a moderately rough dirt road. When I unloaded the 002A I started it up to see what was up. Instead of the output voltage jumping from 120/240 to 155/310 and back like it did at his house, the voltage was a steady 155/310. After about 10 minutes I shut the generator down. At that point I thought it may be a loose connection that bumping down the dirt road may have made even looser. I loosened and then tightened all screws on all terminals. I also tightened and tested all ground connections between modules. That did not help.

Then thinking the problem was Q3 on the VR board I replaced Q3 with a known good one but that did not help. Since I have a spare "reconnect" box for a 002A that I know is good, I replaced the reconnect box with the known good one. Voltage was still 155/310. I assume that means the problem is not in the reconnect box and the problem is not Q3 on the VR board. After that I stopped for the day.

The next day when I got home from work I fired the 002A up and there is no voltage output what so ever. It "broke" just sitting there. No amount of field flashing or holding the start switch in the START position will give any voltage output.

Since I replaced the reconnect box with a known good one and since I replaced Q3 on the VR board with a NOS transistor with no change, does anybody have a recommendation what I should do next?

I have the TM's but due to work and other obligations it will be the middle of next week before I can pour over them. I am a bit frustrated because I screwed up my friend's 002A and I would like to get it working for him ASAP.

Any pointers would be greatly appreciated. Thanks

Since you replaced the distribution dox with a known good one, then its for sure not the problem. It could be the VR board or the T2 transformer that is next to the VR board. The TM will tell you how to test the T2 transformer (its paragraph 4-38 in TM5-6115-585-12). But unfortunately most of us can not test the VR.

Recently spent several months troubleshooting a MEP-002A that would make very high voltage power when ACVR disconnected but not flash or show voltage with ACVR connected. Double checked everything many times. Had previously put in take off transformers T1,T2, Load Current Reactor, CVT, CVT1 and two different ACVR boards. The third ACVR board solved the problem. What was strange is other ACVRs worked fine on my MEP-003A but NOT this MEP-002A. Quite baffling. May be worth checking.

I just replaced a flaky ACVR on a 016. Sometimes the voltage would be low, then it might jump up higher. I replace the ACVR and it was rock solid and normal.

Posting a little more info in hopes somebody can offer some suggestions......As stated in the original post my friend has owned this 002A for 2 years. The voltage has always been unstable jumping from 240V to 310V and back several times in a typical 30 minute exercise run. I offered to try to fix it - big mistake. First thing I did was to change out the entire "reconnect box" with a good spare. That did not help. Then I replaced Q3 on the AC VR board. That did not help. While the generator was running and showing 310V the voltage suddenly went to ZERO and it has stayed there even after numerous attempts to flash the generator fields. I removed the wire from terminal 17 on the AC VR which is supposed to bypass the AC VR. That did not help.

When I start the engine and hold the start switch in the START position to "flash" the fields, I get 24V to the generator fields but no indicated output voltage on the panel meter. I measured 6.4 VAC at 60 Hz at the convenience outlet. The Hz on the 6.4V varies with engine speed as it is supposed to do. I ordered one of the new and improved replacement AC VR's from "triplejim" but he does not think that is the problem. The AC VR will arrive tomorrow and I plan to install it and see what happens.

What else can cause this problem? About all I can figure is either one or more of the diodes in the generator failed and / or one of the windings in the generator failed.

My advance thanks for any suggestions.

I know this is a dumb question but are you sure your test meter is reading right? I've had some goofy meters in the past that didn't read as they should, no voltage reading when there was voltage. Once I realized that I had a whacky meter, I'd usually throw it in the garbage. Those kind of meters will get you killed.

Another idea, do you have another generator to borrow known good parts from for test and to verify questionable parts as good or bad?

Thanks - The test meter is Fluke 87 IV which is very accurate. It reads AC voltage and Hz. I do have a couple of working 002A generators that I can swap some parts off. If the AC VR from triplejim does not solve the problem I may have to resort to part swapping.

I remember when the Fluke 87 came out. I preferred my True RMS beckman over it because I didn't like the delay of the auto-ranging feature. I'm kind of like GuyFang, I want to see instantaneous changes. My Beckman isn't quite as fast as old analog meters, but it's close. I've had that darn thing for like 35 years now. I'll be heart broken if it ever bites the dust. I haven't looked at my 002 yet but I believe the 016, 002 and 003 all use the same ACVR. I read that somewhere in the specs. That's how I finally diagnosed my 016B, I swapped in a known good from my 016E to confirm my diagnosis.

The Fluke 87 has a range button that will lock the range to whatever one you want. It also has a fast-response bar graph for indicating rapid changes that you might not be able to read on the digital display.

Triple Jim said:

The Fluke 87 has a range button that will lock the range to whatever one you want. It also has a fast-response bar graph for indicating rapid changes that you might not be able to read on the digital display.

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Thanks - I have been a ham radio operator since the 1960's. I have built some of my own gear and I do a LOT of troubleshooting and repairs for other hams. However this 002A is getting the best of me. I really think the problem is a shorted winding OR a winding that checks OK with a volt-ohm meter, but breaks down under voltage. I do not have a megger. One of my many hobbies is restoring old broadcast, ham, and shortwave radios from the 1930's to the present. I have around 100 of them on display in my "game room". I have two Fluke 87 digital meters, two analog Simpson 260's, a HP 412 VTVM, and an analog Triplet 630. Not being a butt, but I know how to use the various meters and the limitations of each one. I do appreciate all the replies and the ideas. I have not given up - yet. If I don't get this 002A going in a while, it will become a parts donor for other 002A and 003A generators. Engine runs well. "Reconnect box" works. LOTS of good parts if I give up.

Hang in there. Sounds like you have all the skills and equipment to figure it out. It sounds like it's going to be one of those tough ones you just got to keep at till you get to the end of the road.

jamawieb said:

Since you replaced the distribution dox with a known good one, then its for sure not the problem. It could be the VR board or the T2 transformer that is next to the VR board. The TM will tell you how to test the T2 transformer (its paragraph 4-38 in TM5-6115-585-12). But unfortunately most of us can not test the VR.

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Have you tested T2 transformer? Also make sure your grounds are good.

quad4u said:

I have two Fluke 87 digital meters, two analog Simpson 260's, a HP 412 VTVM, and an analog Triplet 630. Not being a butt, but I know how to use the various meters and the limitations of each one.

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I was actually responding to 87Nassaublue's post, in which he said he doesn't like the auto-ranging and resulting slow response of the Fluke 87.

Triple Jim said:

I was actually responding to 87Nassaublue's post, in which he said he doesn't like the auto-ranging and resulting slow response of the Fluke 87.

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I never intended to "insult" anybody, especially those who are trying to help. All I meant is I have numerous VOM's and no one is best for all jobs. Actually I prefer analog VOM's but digital VOM's definitely have their place. A good digital VOM is probably best for reading a stable voltage. Analog VOM's better for reading voltages that are changing and for peaking or nulling circuits.

This is just me, but I would take a look at the main gen. If you replaced the "reconnect box", there just ain't much else to look at. After all, its more or less the whole ball of wax, in the box. Normally I would have said look at the S-8. These kind of problems sound like S-8. But that's been swapped out also. Got to think this out, on this one.

UPDATE - After installing a new "reconnect box', replacing Q3 on the ACVR, installing a new ACVR, checking T1 and T2, then replacing the entire "gauge box" with a good one, and checking all grounds etc with no success, I took a break. All this tells me the problem must be in the generator itself. Today I removed the sheet metal cover from the end of the generator. This exposes the stator, rotor, windings, and the diodes. Everything looked good and really clean and there was no evidence of burned windings from a visual inspection and a "smell" test. While poking around I found the wire going to the solder lug on one of the diodes was broken or burned off and just barely touching (or not touching) the diode solder lug. Dark came before I got to try to resolder the wire to the diode lug. That area is crowded and very hard to get to so resoldering the wire back on the diode will be a challenge. Of course this diode and the others may be "bad" but only time and more testing will tell. Has anybody ever removed and replaced these diodes without removing the generator and engine from the frame? That looks like the only way to get to them. Also does anyone have a generic part number for these diodes?

Like Thomas Edison said when trying to perfect the incandescent light bulb, "I have not found the right filament material, but I know of hundreds of filament materials that won't work". That is about where I am now. I am not sure exactly what and how much is wrong with this 002A but I now know a hundred things that ARE NOT wrong.

I will keep plugging away.

That's very interesting! Are there any numbers on the diode? If we can find the specs, perhaps we can cross it to something.

No numbers that I can find. Having been in electronics all my life I imagine from the application that these stud mounted diodes are just generic diodes that can be purchased for a few dollars each. All I really need to know is the amp rating. Most any 1000 PIV stud mount diode should work as long as its amp rating is large enough. But then I may not need new diodes. Time will tell.

That's what I was thinking. It should be a standard diode if you can just figure out what it is. By the way, I just ordered a bridge rectifier from China, because that's the only place I could get it. It had a 150 am rating but when I got it, it doesn't read like a normal bridge rectifier. I'm not reading any continuity. on it anywhere. I'm thinking certainly there's something I'm missing but it's just a big rectifier. No continuity normally means bad.

cuad4u said:

UPDATE - Also does anyone have a generic part number for these diodes?.

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From the General Information Wiki page located at:

http://www.steelsoldiers.com/showthread.php?62648-MEP-002A-and-003A

The generic part numbers are:

Rotating Rectifier Diodes

Cross Reference:
#27 NSN...5961-01-050-7048... 1N1204RA Semiconductor Device, Diode

#28 NSN...5961-01-054-4151... 1N1204A Semiconductor Device, Diode