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Generators In this forum we will try to answer any of your questions about the different model generators that can be found on Blue Bird coach's.

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  #1  
Old 08-26-2010
stanley7140 stanley7140 is offline
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Default Onan 8Kw Engine Monitor PCB

Last winter I had to replace the engine monitor PCB. The K12 dual relay was melted, and several traces were burnt- bad. I found several wires in the cannon plug that were bad. I figured that was the problem. I fixed the wires, and replaced the board with one from flightsystems. No such luck. After putting about 50 hours on it, I burned a trace on the new board.

I think that a bad DC Control Breaker (CB11) alowed this to happen. The red rocker has been missing since I got it, and I suspect it is corroded inside and didn't trip. I'm trying to figure out what caused it to happen. The trace that burned feeds the fuel solenoid(K1) and the fuel pump(K5) through CB11, B+, and K12. The set had been runninig for about an hour when the PCB smoked and the gen died. (cold shower next morning).

I disconected the wire feeding K1 and K5 and put power directly to it. I ran is about 30 minutes and it never drew more that an amps or so.

Has any one had trouble with the fuel pump locking up and drawing too much intermitantly? Or had anything like this?

Thanks
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Dave in Oregon
1988 FC35SB
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  #2  
Old 08-26-2010
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Bill Pape Bill Pape is offline
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If there are fried wires at the cannon plug, there may be a short in the wireing inside the Bird, disconnect the plug that feeds the gages and the On/Off Start switches.
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Bill & Patty
1988 FC, Silver Edition
Commerce, Michigan
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Old 08-26-2010
Jim Brookshire Jim Brookshire is offline
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Just a thought for some of you guys who are having trouble with the circuit breakers on the Onan generator control box vibrating apart. After having the same issue with mine, I replaced them with fuse holders and standard automotive blade fuses. A small simple aluminum plate bolted where the circuit breakers were located to mount the fuse holders. The ones I bought have water proof covers and have been trouble free for 4 or 5 years. Much cheaper than replacement circuit breakers and nothing to vibrate apart.
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2001 LXI
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  #4  
Old 08-27-2010
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Jim,

Good idea , I have replaced these CB's on my Onan & McGinnis' Onan, & suggested these rascals to others.
They are still sometimes a problem, but know where to look first when it will not work.,
Will use your fix next.
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1988 FC, Silver Edition
Commerce, Michigan
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  #5  
Old 08-29-2010
rmp319 rmp319 is offline
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Default 8k Onan

I am looking at a similar situation as Stanley. Checked everything out, replaced the board with a flight system PCB and smoked it immediately. I don't like taking this into a shop because most shops do not understand the BB systems so you end up paying for the learning curve. I did not see any bad terminals on the cannon plug but will recheck.
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Robert P.
1990 36SP
Tyler, TX
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  #6  
Old 08-29-2010
Mikel Mikel is offline
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Just had a problem with the 8KW Onan in my 89 SP, It would crank for about 2 minutes ( in 10 to 15 second intervals) before starting. Checked the lift pump, injector pressure and then discovered that the glow plugs were not working. I jumped from the starter to the glow plugs and with 10 seconds of preheat it started imediately. Since I replaced the cb, which physically broke a month ago, and that is the source of current for the glow plug switch, I traced it out from there to the cannon plug, J2. The pins J2-10 (the glow plugs) and J2-11 (B+) were fried. I plan to bypass the cannon plug and put a grommet in to run the wires direct. There is a large amount of current passing though the glow plug wiring, and I suspect that the relay and wiring and especially the cannon plug can be damaged by using the preheat for more than the prescribed time. Also, resistance in J2-11 could cause lower voltage and increase amperage in the rest of the contol box leading to other failures. Just a guess.
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Mike & Debbie Lyons
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89 SP36
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Old 08-30-2010
rmp319 rmp319 is offline
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Looking at the back of the original ONAN PCB the burnt trace goes from the B+ to the J11 B+ terminal, the same happened with the Flight System board. I spoke with a tech at Flight Systems and if I explained the problem correctly he thought there was a power surge across the board. It ran about 2-3 minutes on the second board before self destructing and I noticed only one leg was registering on the load gauge during the run. Will look at the glow plugs and see if this is the source.
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Robert P.
1990 36SP
Tyler, TX
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  #8  
Old 08-30-2010
rmp319 rmp319 is offline
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Default Schematic Flight System

This is from Flight System
Attached Files
File Type: pdf 300-2604.pdf (132.6 KB, 403 views)
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Robert P.
1990 36SP
Tyler, TX
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  #9  
Old 08-30-2010
stanley7140 stanley7140 is offline
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Jim, thanks for the advice. Had I not already purchased the circuit breakers, I would have installed fuses. Next time.

Robert, if you haven’t replaced the circuit breakers yet, you should follow Jim’s advice. The circuit breakers should protect the B+ circuits on the board. If the board burned up, the CBs must not be working.

Bill, you get the prize for best guesser.

I was able to repair the PCB by soldering a wire across the burnt trace. The Flightsystems board is better that the original, and somewhat less complex and more robust. After replacing the CBs, I put a 10 amp fuse down stream between the PCB and the fuel solenoid and fuel pump. The generator started and ran fine. After a few minutes I noticed the temp gauge was acting strange. I tapped the glass and the generator quit. The circuit breaker trip, protecting the PCB, and the 10 amp fuse was fine. Turns out a screw had come loose from somewhere and landed on the back of the temp gauge. As it bounced around, sometimes it would short.

What I did wrong was not replacing the circuit breakers the first time the board burned up. If the CBs were working, the second board would not have burned up, and I could have diagnosed the problem as the CBs tripped.

TTFN
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  #10  
Old 08-31-2010
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Thanks for the follow-up , another mystery solved.
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