Onan 6.5K stopped runinng

jwrape · Post by **jwrape** » Wed Aug 13, 2008 2:22 pm

Well I justhad it running on Saturday night. I go to start it up on Sunday and it wouldn't. It would turn over but not fire EXCEPT when I turn the starter switch to off, it has a brief spark enough to TRY to start.
So to re-cap, I flip the switch to start/run and it tries to start but doesn't, AS I am flipping back to the off position the motor fires for a brief moment.

I took the spark plug out and held it against the head and saw when I turn the switch from Start to Off, it sparks one time and then dies.

Well later after we got out on the water I messed with it again and found that there was only about +3v coming from the control box to the thermal switch that feeds the +12v to the coil. I pulled the thermal switch off and checked it, it is good. I pulled the 12v supply off, connected a wire from the battery to the coil and the motor started right up and ran fine BUT with a large load it would bog down really easy.

I followed that lead back to the inside of the control box and it is connected to a tall cylinder "thing"

I have pics of all this but can't access them from here at work to post them. I will post later.

Any ideas why the control box would stop supplying the +12v to start the generator? Let me re-phrase that, it supplies power to the starter to turn the motor over, but not +12v to the coil to run the motor.

Don Lumber · Post by **Don Lumber** » Tue Aug 26, 2008 8:07 am

Any news for us on this one?

jwrape · Post by **jwrape** » Wed Aug 27, 2008 12:58 pm

Well, no not really. I hot wired the coil to the battery and it will run but Weird thing is, it BOGGS down really badly with the Heater breakers on and the heaters aren't even on. Can't run the A/C units or it boggs, but then again it will run the Fridge and the microwave and the blender without issue. So basically it will run with the coil straight wired to the battery but not strong and it WON'T RUN with it connected to the control box as it should be. I haven't been back out in a couple weeks because of the weather Tropical storm FAY, but I am going out there Friday and will change the oil and try to trouble shoot somemore. I am really getting fed up with this thing.
The wire that comes from the control box to the coil that SHOULD supply +12v to the thermo switch then to the coil is only giving +3v instead of the +12v. Don't know why yet, but my Father is gonna come over and take a look. He has worked on this thing a million times as well, maybe 2 heads are better than one. Crossing my fingers, I haven't been able to use this thing all season.

Don Lumber · Post by **Don Lumber** » Wed Aug 27, 2008 2:21 pm

Man, with everything I read about these things I'm not sure I even want to work on mine. Maybe I should pull it out and replace it with a nice big battery bank.

jwrape · Post by **jwrape** » Wed Aug 27, 2008 2:26 pm

Don Lumber wrote:Man, with everything I read about these things I'm not sure I even want to work on mine. Maybe I should pull it out and replace it with a nice big battery bank.

Oh, it's not that bad. Just old GenSet. Old will always give you issues.

jwrape · Post by **jwrape** » Wed May 20, 2009 7:16 am

Well I believe we found the issue:::: YEA!!!!!!!

I had the Cummins South technician come out and service my GenSet on Monday at $99/hr...

He starts by saying, "You know every part on this thing is obsolute?"
I said yes but I'm hoping you can tell me what's wrong and I can find the old part on Ebay or something.
SO, he got started and he traced the power from the coil back to it's source and pulled out this little 1.5" x 1.5" card labeled Onan300A734.

He put the test leads on the top resistor 470 ohm resistor and the FLuke meter went all over the place and then went to an open. He tested the other parts ont hat board and they were good. Upon closer look you could see that the resistor had gotten hot and bled around the leads.

So the Tech says you are getting out cheap. Replace this $2 parts and you should be up and running.

So he leaves and says he's only gonna charge me for an hour and a half. Not too bad. Ended up being $243 some how. I guess taxes or something I didn't get a receipt yet.

Anyways, I went to 2 Radio Shacks to try to find the resistor and they said I would have to order it because it was a 2watt resistor and RS only sold up to a 1/2 Watt. So I was driving home to look this up on the internet and order it when I drove by an old TV repair shop. I stopped in and asked him it he had the resistor. Thank the lord he did. He charged me $3 for it and it's a 2% tolerence as opposed to the 5% tolerence that was on the board. I replaced it and now I only need to slip it back in this weekend and it SHOULD start right up, God willing and the creek don't rise.

Now after new resistor

aaronbocknek · Post by **aaronbocknek** » Wed May 20, 2009 8:47 am

looks to me like a load sensor control board. as you know, i had problems with my 1976 MCCK 6.5 hunting when a load was put on it. not your typical hunting, but to the point where it would almost stop. i upped the engine rpm and that took care of it a bit, but, when i shut her down, it tripped a 50amp breaker in the bilge (goes from the control-o-matic) to the main electrical panel and blew a .25amp, that's right, a .25amp fuse in the load sensor control board ( knew that when i was doing a continuity test of all the boards). i did have a tech come out a few weeks ago to look at it, and sure enough, it was the 'surge' that went back into the breaker box and the small circuit board. i had a supply of .25 buss fuses (thanks to baynesville electronics here in baltimore (http://www.baynesvilleelectronics.com). the tech showed me how to up the engine rpm while reading the volt meter to get the no load and load speed. we put in the new fuse, flipped the breaker and then started her up then switched to 'gen' and i get power to the boat and it works okay.... well, atleast for now. he also took off the old carb and rebuilt it as it was leaking. total for the travel time twice and rebuild was around 500.00 but well worth it. he did say though, ''i just wish more people would run their generators. that's what they are designed to do and the less it is used, the more problems crop up." he suggested that by running the genset 30 minutes each week at 50% load should keep everything running. he did caution though, ''even though it is rated at 6.5kw, thats not a constant and rule of thumb is 60 to 70% rated load max" the constant output is around 5kw.

jwrape · Post by **jwrape** » Wed May 20, 2009 8:53 am

aaronbocknek wrote:looks to me like a load sensor control board. as you know, i had problems with my 1976 MCCK 6.5 hunting when a load was put on it. not your typical hunting, but to the point where it would almost stop. i upped the engine rpm and that took care of it a bit, but, when i shut her down, it tripped a 50amp breaker in the bilge (goes from the control-o-matic) to the main electrical panel and blew a .25amp, that's right, a .25amp fuse in the load sensor control board ( knew that when i was doing a continuity test of all the boards). i did have a tech come out a few weeks ago to look at it, and sure enough, it was the 'surge' that went back into the breaker box and the small circuit board. i had a supply of .25 buss fuses (thanks to baynesville electronics here in baltimore (http://www.baynesvilleelectronics.com). the tech showed me how to up the engine rpm while reading the volt meter to get the no load and load speed. we put in the new fuse, flipped the breaker and then started her up then switched to 'gen' and i get power to the boat and it works okay.... well, atleast for now. he also took off the old carb and rebuilt it as it was leaking. total for the travel time twice and rebuild was around 500.00 but well worth it. he did say though, ''i just wish more people would run their generators. that's what they are designed to do and the less it is used, the more problems crop up." he suggested that by running the genset 30 minutes each week at 50% load should keep everything running. he did caution though, ''even though it is rated at 6.5kw, thats not a constant and rule of thumb is 60 to 70% rated load max" the constant output is around 5kw.

Yea, I would definately run mine more often if it ran. I could have REALLY used it last season and now this season I'm sure we will use it all the time.
Since mine is a 74' The electronics are fairly simple just ugly and tangled making it hard to troubleshoot but the Cummins Tech was able to trace the power back to that little board.
He made the comment that my Gen really didn't have a Control board, it was more relays, resistors and diodes...
He said they made a digital control box but it was over $1000 and I might as well replace the entire generator due to the age of mine.

Funny when my dad originally boat the boat 8 years ago the Gen didn't run and wouldn't do much of anything. He pulled the heads and found the valves stuck. He cleaned them with some emory paper and re-assembled them and it started right up but he had to disconnect the choke cause it would flood it out.

I figure if the motor runs well and it makes power, there is no reason to replace it. Just fix the electronics and run it....

aaronbocknek · Post by **aaronbocknek** » Wed May 20, 2009 9:12 am

i totally agree and so did the gentech that worked on mine. he works for cobe marine in pasadena md and the two guys (joe and tom -- the tech) install new kohlers and westerbekes and rehab old onans. when they remove and old onan, they take all the parts that are worth anything and rebuild them. it was fascinating to watch this guy use the volt meter to see if the stator was producing power and what the voltage was as he adjusted the throttle on the carb. he let me assist as he said that this was the only way for an owner to get involved in his boat. it also gave me a better understanding as to what exactly does what. when i popped open the control box, i was amazed at the diodes and resistors and mass of wires and old circuit boards. my nephew is an electronics whizzkid and would have a field day with this. hell, he could probably rebuild the damm thing board by board.... i actually have the tech/parts/service manual and it explains what all the boards do and what the ohms for each diode and relay are. if you need any of that, i can copy it and send it to you. i have to admit though, the board did as it was designed to do 30+ years down the road.... when the volts were too much from my initial messing with the rpm, it blew the breaker and then the buss fuse to protect the diodes and relays. did he say to you that you could have a new control box put on this one? a grand to have it running rather than 15K to put a new one in might be a good investment later down the road.

jwrape · Post by **jwrape** » Wed May 20, 2009 9:23 am

aaronbocknek wrote:i totally agree and so did the gentech that worked on mine. he works for cobe marine in pasadena md and the two guys (joe and tom -- the tech) install new kohlers and westerbekes and rehab old onans. when they remove and old onan, they take all the parts that are worth anything and rebuild them. it was fascinating to watch this guy use the volt meter to see if the stator was producing power and what the voltage was as he adjusted the throttle on the carb. he let me assist as he said that this was the only way for an owner to get involved in his boat. it also gave me a better understanding as to what exactly does what. when i popped open the control box, i was amazed at the diodes and resistors and mass of wires and old circuit boards. my nephew is an electronics whizzkid and would have a field day with this. hell, he could probably rebuild the damm thing board by board.... i actually have the tech/parts/service manual and it explains what all the boards do and what the ohms for each diode and relay are. if you need any of that, i can copy it and send it to you. i have to admit though, the board did as it was designed to do 30+ years down the road.... when the volts were too much from my initial messing with the rpm, it blew the breaker and then the buss fuse to protect the diodes and relays. did he say to you that you could have a new control box put on this one? a grand to have it running rather than 15K to put a new one in might be a good investment later down the road.

He said they make a universal Digital Controller that he "Thinks" would fit but it's expensive. When I asked if it cost something like a $1000 he said "a little more. "
He said my old controller is simpler and easier to fix although all the parts are obsolute, it's easier to fix if you are resourceful.

To me, before I would buy a new controller for mine I would buy a newer used GenSet. I would never buy a new one anyways. I am a stickler for NOT buying anything new if I can help it. I just don't like taking the hit on a new items depresiation(<Spelling).

But for $3-5k I could probably pick up a decent used GenSet.
But as I told the Tech, if I'm gonna replace the genSet, I'm also going to replace the Water Heater and the Fridge and all the other LARGE stuff in the boat because to do so I would have to remove the headliner, the hatches, carpet, the roof and pull the boat out of the water to do it all so then I would paint the bottom and put in my thru hull transom lighting and then I would be out $20k+++.

I'm not ready for all that. LOL!