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Onan MAJB Marine 3kw- shut down


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  #1  
Old 11-01-2007, 11:55:15 AM
rocked rocked is offline
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Default Onan MAJB Marine 3kw- shut down

I guess it's never ending when you use something!

So the gen was running like a champ, and we were anchored out enjoying the TV on Saturday night, when the power just went off. Then the generator shut down. It will start and run as long as the Start button is depressed.

From searching the forum, it sounds like it isn't producing power, but what I'm wondering is does the symptoms "while there was a medium load on it, it stopped and then shut down" point to anything specific?

I will take a multi-meter up next time I'm there and check for sure. I did pull the 3 fuses on the front panel, all looked good. I also flipped the breaker switch on the side of the panel. Also checked the oil and disconnected the temp sensor.
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Old 11-01-2007, 03:01:33 PM
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Elden DuRand Elden DuRand is offline
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Default Re: Onan MAJB Marine 3kw- shut down

You might have lost oil pressure or the oil pressure shutdown switch has died.

Make sure oil pressure builds up right after starting - THEN - remove the wire from the oil pressure switch and see if the genset starts and runs normally.

I've got an auto oil pressure gauge with a piece of small copper line attached with a 1/8"NPT fitting on the end. I just remove the oil pressure switch and screw in the gauge line. Now, with the wire off of the switch, I start the engine and check the pressure.

Run the engine as little as possible until you're -SURE - you have oil pressure.

If the switch is bad, you can get one at an auto parts store.

Take care - Elden
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Old 11-05-2007, 10:34:15 AM
rocked rocked is offline
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Default Re: Onan MAJB Marine 3kw- shut down

I took a mulitmeter up this weekend and no voltage is being produced
(Plus side is she fired right up after sitting for a week...then just died as soon as I let go of the start switch)
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Old 06-30-2008, 10:54:31 AM
lciambotti lciambotti is offline
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Default Re: Onan MAJB Marine 3kw- shut down

I am having the same issue. Same Genset. I tried the the oil switch, checked the oil pressure (over 40 lbs), replaced the exhaust high temp switch. Still won't run when I let the start switch go. This happens whether or not I use the remote start switch or the switch on the genset. Anyone have any ideas?

Thanks
Leon
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Old 06-30-2008, 04:13:31 PM
rocked rocked is offline
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Default Re: Onan MAJB Marine 3kw- shut down

I ended up replacing the bridge rectifier....I'll look around and see if I have a part number. The BR takes the AC current of the alternator and converts it to DC to create the magnetic field (someone correct me if I'm stating this incorrectly.) To get to it, I removed the cover on the control panel, then the gen end cover. (going from memory here). It's a black square about an inch across with 3 terminals on it. If I remember, you can connect an ohm meter to 2 of the terminals (upper right and lower, then upper left and lower) to get a reading. If either of these don't have a 'path', the BR is bad.
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Old 06-30-2008, 07:49:30 PM
Gunny Gunny is offline
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Default Re: Onan MAJB Marine 3kw- shut down

How about posting the whole model/spec/serial number so we see what you see.
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Old 07-02-2008, 12:52:21 PM
lciambotti lciambotti is offline
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Default Re: Onan MAJB Marine 3kw- shut down

Thanks. I'll look for the BR. Problem is, where the gen. is located its pretty tight. Not sure if I can get to the end cover. I'll report back!!
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Old 07-03-2008, 10:22:48 AM
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Default Re: Onan MAJB Marine 3kw- shut down

For generators in boats, it helps to be a contortionist. Mine was not easy to get to either. Likewise, the timing mark is on the underside of the flywheel necesitating me hanging upside down in the compartment to set the timing.

A little more on the BR. When your start button is depressed, DC voltage is applied from the battery to energize the generator field. Once the generator is producing electricity (AC) and the start button is released, AC is passed through the BR (2 inputs) to the dc output to maintain the gerator field. Think of the BR as a 1 way Y valve. The AC from the 2 poles of the generator are passed to each of the inputs (alternating from one to the other) and out the output as 1 steady stream (DC). The BR Y valve is also only 1 way...so that voltage from the opposite AC path cannot backflow into the other.
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Old 07-11-2008, 03:47:34 PM
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Default Re: Onan MAJB Marine 3kw- shut down

Any updates?
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Old 08-25-2008, 10:30:21 AM
lciambotti lciambotti is offline
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Default Re: Onan MAJB Marine 3kw- shut down

I replaced the BR yesterday but it didn't help. Actually now it won't even start while holding the start button. I am very frustrated!!!! I've checked and rechecked all my wires, and I just can't find anything.
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  #11  
Old 08-25-2008, 11:53:15 AM
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Billy J Shafer Billy J Shafer is offline
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Default Re: Onan MAJB Marine 3kw- shut down

Post model and serial number. Onan did have a problem with the relay in AJ.
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Old 08-25-2008, 04:51:21 PM
lciambotti lciambotti is offline
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Default Re: Onan MAJB Marine 3kw- shut down

I'll have to stop by the boat and get them. I left the manuals on it!

Thanks
Leon
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Old 08-25-2008, 08:14:26 PM
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Billy J Shafer Billy J Shafer is offline
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Default Re: Onan MAJB Marine 3kw- shut down

One thing I do not miss being retired. Working on boats. I have had several offers to work on some.But I always seem to get sick.
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Old 08-27-2008, 01:52:20 PM
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Default Re: Onan MAJB Marine 3kw- shut down

I went to the boat this morning. The generator is a 1R/1B. I didn't see a serial number. For me, I get sick thinking about working on a boat!!

Thanks
Leon
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Old 08-27-2008, 02:51:14 PM
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Default Re: Onan MAJB Marine 3kw- shut down

I will share my feelings about working on a boat.
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  #16  
Old 08-27-2008, 03:22:22 PM
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Default Re: Onan MAJB Marine 3kw- shut down

There's always work to be done on a boat! Like open a cold one!

It's a damp, harsh environment, but the payoff is wonderful! I always carry a spare on board: a spare everything!
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Old 08-27-2008, 03:26:22 PM
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Default Re: Onan MAJB Marine 3kw- shut down

Sounds a little suspicious that it would start with the button depressed before you replaced the BR but now won't I get frustrated easily, have to walk away, and come back next week...of course then I ponder what's really wrong all week and surf the forum...

I also wasn't thrilled with the fact you had to open the control panel to remove a couple of screws to get the gen end off either...

Hopefully someone here can provide some additional insight...
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Old 10-27-2009, 04:48:49 PM
qvctrucker qvctrucker is offline
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Default Re: Onan MAJB Marine 3kw- shut down

Maybe the stator is bad.
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Old 10-29-2009, 11:01:35 AM
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Default Re: Onan MAJB Marine 3kw- shut down

I have the same problem with my geset and I am looking for sugestions on how to fix it .
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Old 03-15-2010, 01:40:20 PM
ferrari360 ferrari360 is offline
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Default Re: Onan MAJB Marine 3kw- shut down

I was having the same problem with my generator and was wondering if anyone found the cause. I have a 3.0 MAJB. It only runs when you hold the start button and dies as soon as you release. I think I have done it too many times and fried the starter relay. Any and all information is greatly appreciated as I am trying to get it working for the upcoming boating season.
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