MEP-016B trips DC circuit breaker

87Nassaublue

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OK guys, I need some advanced advice.

I've recently acquired a MEP-016B Onan generator. I've repaired a long list of fuel system issues already. Now, I can get generator to start and run by holding the fuel shut off solenoid as if it were energized. I tried jumping in 24 volts to pull the solenoid in but it didn't pull in and I drew excessive current with the jumper.

I realized the low fuel level switch was bad and wouldn't complete the low fuel circuit. I shorted pins D and E at the switch and tried to start it and the DC circuit breaker tripped immediately.

After more head scratching and study of the schematic, I see that one side of the switch goes to A1-TB2 pin 9 which is ground. The other side goes to the control circuit board, A3-TB2 Pin 1.

Logic would dictate the wiring harness is not shorted to ground since one side of the circuit is ground and unless the switch is closed or bypassed the circuit breaker does not trip.

So, it would seem the problem is either on the circuit board or related to it.

Have any of you guys experienced a similar problem?

Do any of you have a schematic of this A3 board? It doesn't look very complicated. You'd think there'd be a schematic of it somewhere.

I can see now why this one was DMRO'd. My other E model one only took an hour or two to get it going perfectly. Every time I repair one thing on this B model , it just leads another issue. The engine runs great but good grief what a PITA. I haven't been able to even test the generator portion yet.
 

Suprman

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Try disconnecting the small electric fuel pumps and see if the breaker still trips. I have seen those pumps short a few different times, not on a 016 but on the mep 002 and 003 and the DC breaker always trips like that.
 

Guyfang

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I uploaded the TM's for the MEP-016B in the TM upload section today. Schematics are in the -12 manual. Not sure the A3 board is broken out, but there should be enough there to work it out. If ever a gen set was unbeloved, the 016B was king of the hill.
 

87Nassaublue

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Thanks Superman, I'll try that.

Guyfang, that's funny, I can see why. It's not that complicated but with just enough important information missing they make you work for it! Thanks for uploading the manual.

Apparently what ever actually failed is what took out the contacts on the low fuel shutoff switch.

I'll check some more things and get back with you guys. Thanks!
 

Guyfang

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In the 20 years of my army career, and 8 years as a contractor, I never once saw a 016B actually running. Every one I saw was in a corner, non-op. Tank bone dry. The 016A, 016C and 016D all seemed to have better Karma. Oh well, keep working on it and you will get it up on its feet.
 

87Nassaublue

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Thanks Guyfang, I see exactly what you mean. Getting these things going takes someone with patience, knowledge, resources and a very hard head. I've found the manuals have many typo's, especially the technical training curriculum I found on line. That document had excessive mistakes, but it was instrumental in me making progress. I can see why this thing was DMRO'd.

OK for a grocery list of what I've fixed so far:
1. replaced two fuel lines since they had rotted off the machine.
2. I replaced a governor linkage end because it was broken.
3. the fuel transfer pump wouldn't pump because the shaft was jammed by the gasket. The hole was too small and bound the plunger when tightened down.
4. The injector pump would pump because the fuel cut off valve was seized. I had a **** of a time figuring out how to get that out and finally figured out it had to be freed and centered before it could come out. Got that working and fuel to the injector if I held the shut off solenoid back. It finally ran holding the solenoid back.
5. Ok now figured out the fuel cutoff circuit had issues and tripped the breaker if I jumped the fuel low switch to complete the circuit. I thought I had problems with the switch but now that is working. In order to troubleshoot this circuit, I needed a schematic of the A3 board which apparently is not published. I found the Training curriculum and was able to draw the circuit based on that, the schematic under the lid and the actual wiring.

In tracing the circuit and testing each component, I made it all the way through the circuit. In looking for the short, I slapped the A3 board a few times and found the resistance changed and the short went away Now the fuel cutoff solenoid now works with the main switch,
6. Now the auxiliary fuel pump doesn't work. Back to reverse engineering the A3 schematic. I never did figure out that circuit for certain because of all the mistakes in the literature, but I got enough to figure out there was a bad connection on the A3 board by the relay socket. I got the board out and found cold solder joints on the K3 relay for the FCS and I believe it was K2 for the auxiliary fuel pump.
7. I re-soldered the bad connections on the relays and now both circuits are solid. OK so now I the engine starts up, runs great and acts normally.
8. I set the frequency and find my output voltage is low. After much troubleshooting I find the voltage regulator A1VR1 is flaky and needs replacing. I confirmed that by swapping in a good one from another unit. OK so now running good and making proper voltage.
9. Oh, forgot to mention I reconnected the main ground which had been cut clean for some reason.
10. Ok, so now I think I'm done and I remember I didn't check the battery charging voltage. I fire it up again and wouldn't you know it, it's not charging.
11. So now, I go back and find the bridge rectifier A1VR2 has both diodes blown out on the positive side.

WOW, I'm tired! I can see why someone else gave up on it. This is crazy! So, I have a voltage regulator on the way off ebay and I have to find a big honking bridg rectifier to replace A1VR2

So, anyway, thank you guys for giving me some pointers to get started. When I get Time, I'll try to clean up my drawings and get them posted.
 

Guyfang

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You are rocking! It never hurts to resolder any TB's on a card when having problems. Can't you make a bridge rectifier? If only the + side diodes are bad, you might just try and solder in two replacements.
 

87Nassaublue

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You are rocking! It never hurts to resolder any TB's on a card when having problems. Can't you make a bridge rectifier? If only the + side diodes are bad, you might just try and solder in two replacements.
I guess I could repair the half of the bridge that is blown, but I got a new 150 amp rectifier coming from China for like $9 bucks so what the heck. Probably if I dug into my spare electronic parts at the other house, I have what I needed on the shelf to replace that part, but since I'm also waiting for the main voltage regulator for the genny portion I just ordered new.

I tell you what, that thing was a pain in the donkey to work through all the issues, but I couldn't let that thing get the best of me. It took me a good while but I think I've got it whipped into submission!
 

Guyfang

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You know, that's the way I always felt, when working on gen sets. 20 plus years in the army, ten years off and on for the germans, and almost ten years as a contractor for the US Army. Its a "thing". Metal. I am a thinking human being. I will not, let it get the best of me! I will not say I won every battle, but darned near. Good job.
 

87Nassaublue

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You know, that's the way I always felt, when working on gen sets. 20 plus years in the army, ten years off and on for the germans, and almost ten years as a contractor for the US Army. Its a "thing". Metal. I am a thinking human being. I will not, let it get the best of me! I will not say I won every battle, but darned near. Good job.
I like how you think. We are very much alike. I was going to take it as far as to the generator windings. If the windings were toast, I'd sell it for the engine. If it can be 100%, I'm going to make it run and run right! I see now why the yanmar conversions are so popular. It's a much simpler engine and it's balanced much better and is much quieter. When I fired up the onan, it was loud, vibrated a lot more and started walking around on the floor! LOL It does run pretty darn good though. My new main regulator has already from Califormia via USPS, but that darn rectifier hasn't even shipped yet from China or Hong Kong or where ever it's coming from. LOL Wish I could have found a US supplier.
 
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