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Another Onan JB


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  #71  
Old 01-12-2018, 05:23:02 PM
Leon N. Leon N. is offline
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Default Re: Another Onan JB

You should have the correct wiring diagram for your particular JB and just trace the wires through and do not alter any resistor values in the coil circuits. The values used are important for proper operation and spark performance. I would suggest putting a spark plug on each hi tension lead so that you do not over stress the coil windings insulation as mentioned by Len.
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  #72  
Old 01-12-2018, 05:31:39 PM
EnginePat EnginePat is offline
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Default Re: Another Onan JB

Quote:
Originally Posted by Leon N. View Post
I would suggest putting a spark plug on each hi tension lead so that you do not over stress the coil windings insulation as mentioned by Len.
That is just what I did ,I don't want ruin any expensive parts.
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  #73  
Old 01-12-2018, 08:42:51 PM
EnginePat EnginePat is offline
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Default Re: Another Onan JB

So I have been trying to get the schematic for this jb.

7.5JB 3CR14081AD
OTCU40-B/14G
B870876050
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Last edited by EnginePat; 01-12-2018 at 09:32:29 PM.
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  #74  
Old 01-12-2018, 09:39:40 PM
Leon N. Leon N. is offline
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Default Re: Another Onan JB

It might be listed on the factory build sheet. Maybe someone on the Stak can provide that, I cannot.
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  #75  
Old 01-13-2018, 06:27:49 PM
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Default Re: Another Onan JB

Today I did some work on the jb, I had to get the top of the enclosure off and there was no moving the elbows on the muffler ,so the east way was to use a cut off wheel and cut the elbow in half.then cut it down to the threads and knocked it off. The muffler came right off and the top. I cleaned all the crap out of it, sand everywhere. Blew out the cylinder fins (old mice insulation ) I put a different demand regulator on it and shut off valve.
So I started trying to figure out why no power to the coil. I hooked the battery up and started checking. First i cleaned all the connections. That did not change anything. The gas solenoid has no power. I jumped from the battery to the gas valve and that works, I pushed the start lever and the points had power also by jumping the gas valve. So I went to the k11 black start solenoid, this one has 2 small connections on top and 1 on each side. So I jumped battery power to the left side small connection. At that point I had power to the coil and the gas valve. I do not know the procedure to check the start solenoid but it may be the problem, if anyone knows the way to do it please school me.
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  #76  
Old 01-13-2018, 06:43:56 PM
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BigBlockChev BigBlockChev is offline
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Default Re: Another Onan JB

The "I"terminal on top of the big starter solenoid should have 12V on it when the starter switch is pressed. It is an auxilliary contact which activates when the main relay is pulled in. You can test this by hooking your volt meter to it and pressing the start switch. no volts means it is probably hooped. That part of the circuit is energized only while the starter is turning, once the centrifugal switch kicks in it takes over supplying 12V to the circuit. Hope this is what you are asking about. Cheers Dan
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  #77  
Old 01-13-2018, 06:51:37 PM
Max Thompson Max Thompson is offline
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Default Re: Another Onan JB

Sorry the print is so poor, it is pot luck with the scans, some are great some like this. Some prints do not exist, so I guess this is better than nothing.

During starting ignition power is supplied through K-11. When the centrifugal switch closes and K-11 opens, power must flow through K-12 contacts. Battery - from the start switch to pull in K-11 must also pass through K-12 contacts to pull in K-11.

If K-12 has been abused by the rodent population, it can cause you fits.
Attached Files
File Type: pdf 75 JB 14081AD PAT.pdf (24.2 KB, 19 views)
File Type: pdf 75 JB Pat 612-6070.pdf (374.1 KB, 18 views)

Last edited by Max Thompson; 01-13-2018 at 07:11:05 PM.
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  #78  
Old 01-13-2018, 07:12:12 PM
len k len k is offline
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Default Re: Another Onan JB

That's interesting on the schematic, whats does the vacuum switch do?
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  #79  
Old 01-13-2018, 07:19:04 PM
Max Thompson Max Thompson is offline
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Default Re: Another Onan JB

After re-reading above, it sounds like you have a contact in K-11 that is not good. You can drill the rivets out of the bottom of this relay and take it apart, if you can not find a replacement near by. Replace the rivets with 6/32 screws when done.
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Old 01-13-2018, 07:46:33 PM
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Default Re: Another Onan JB

The large starting solenoid on this unit has 2 terminals on top. I jumped bat power to the left small terminal and that gave me power to the coil and gas solenoid.

Ls......Rs
●| • • |●

K12 seems pretty clean and corrosion free, I did not find any rodent dropping in the control box. I did find a wire that went the the gas valve chafed, it was put thru a small hole that was drilled in the bottom ,it was arched in the spot.
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Last edited by EnginePat; 01-13-2018 at 08:07:16 PM.
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