Onan: Damaged Board or Worse?

P

paul kirsch

New member
Sep 16, 2015
23
1
3
Tucson, AZ
Hi Everyone,

I think I damaged my ONAN control board - or worse - thanks to NOT doing my due diligence on GMCNet! Prior to doing the following, it was running
perfectly :/

First - I noticed one of the voltage regulator tabs had broken free, the one marked 'AC' for the wires coming from the alternator and on to Pin 8 on
the control board. Noticing a second tab also marked 'AC' on the voltage regulator (adjacent to the B+ connector), I plugged in the two ganged wires
there (I now know the VR is not needed).

Second - I gave the entire unit a bath with my garden hose (as is expressly discouraged here: http://bdub.net/gmcmotorhome.info/generator.html).

Third - I started it (still wet) from the switch on the control board. She ran for 15-20 seconds and then there was a flash from the control board and
she quit. The start solenoid was silent from then on. I stowed the unit and let it dry for a couple of weeks.

Yesterday, I discovered a blown fuse on the control board (the flash I saw?) and so replaced it. I also disconnected (from the VR) the two ganged
wires going from the alternator to Pin 8, wrapping and stowing them connected together. The Onan now turns over 3-4 revolutions before the solenoid
disengages, repeating that engage/abort sequence indefinitely as long as the start switch is held (either the one on the board or the remote switch in
the cabin). The Onan's oil level is correct and I've got 20+ gallons of fuel in the main tanks.

I suspect that I fried something on the Onan board, either from miss-wiring to the second 'AC' connection at the VR, or from starting it wet with
water. However, I don't want to fry a replacement board if something else in the circuit was damaged by my miss-deeds. Thoughts?

Thanks!!

Paul

--
1976 Glenbrook with MAC dash, Alcoa wheels, Patterson carb, and A&E awning.
 
Well, Assuming that your Onan board is good, Normally I would say that you either have

1. a bad oil pressure switch, (no oil pressure) or
2. a missing voltage out of the Onan alternator.
It takes input from both of these to keep the Onan running.

1. Normally the oil pressure switch grounds board pin 12 when there is no oil pressure. So if you want to prove that this is not your problem (it
probably isn't your problem), unplug pin 12 from the board, check that the engine oil is full, and try to start the engine. If it does not run then
that is not your problem. Re-install the removed wire.

2. To check for a missing AC voltage put your meter across pin 5 and Pin 8 of the Onan board and set it to read AC voltage greater than 40 volts. We
will be looking for around 30 volts AC. Then jumper pins 5 and 9 together. This will supply continuous 12 volts DC to the fuel pump and the
ignition. Now try to start the engine. It should run and you should be able to read AC on your meter. If you see around 30 volts AC then the
alternator signal is getting to the board correctly and you have an Onan board problem. If it is missing, then you need to go back and look at the
rewiring that you did on the VR because this is the same voltage (and circuit) that you were playing with on the VR.

Disconnect thee jumper form pin 5 to 9 to stop the engine.

I am guessing from your symptoms that either the VR re-wiring is incorrect or that you have a bad board in the area of K2 and the components feeding
K2.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
Good morning Ken

I have my coach at repair station and they are having a bad time keeping
unit running. Could you give Ron Cognac a call and maybe help him out.
915 479 4647, he is getting frustrated with my Onan. his email is
ron

thanks Marcel Bourgon,

> Well, Assuming that your Onan board is good, Normally I would say that you either have
>
> 1. a bad oil pressure switch, (no oil pressure) or
> 2. a missing voltage out of the Onan alternator.
> It takes input from both of these to keep the Onan running.
>
> 1. Normally the oil pressure switch grounds board pin 12 when there is no oil pressure. So if you want to prove that this is not your problem (it
> probably isn't your problem), unplug pin 12 from the board, check that the engine oil is full, and try to start the engine. If it does not run then
> that is not your problem. Re-install the removed wire.
>
> 2. To check for a missing AC voltage put your meter across pin 5 and Pin 8 of the Onan board and set it to read AC voltage greater than 40 volts. We
> will be looking for around 30 volts AC. Then jumper pins 5 and 9 together. This will supply continuous 12 volts DC to the fuel pump and the
> ignition. Now try to start the engine. It should run and you should be able to read AC on your meter. If you see around 30 volts AC then the
> alternator signal is getting to the board correctly and you have an Onan board problem. If it is missing, then you need to go back and look at the
> rewiring that you did on the VR because this is the same voltage (and circuit) that you were playing with on the VR.
>
> Disconnect thee jumper form pin 5 to 9 to stop the engine.
>
>
> I am guessing from your symptoms that either the VR re-wiring is incorrect or that you have a bad board in the area of K2 and the components feeding
> K2.
 
Regarging the wires by the old voltage regulator--- the 2 faston connectors on the "Twofer" must stay connected together and well taped up. The single
wire gets disconnected and taped up on it's own. This is from memory from the Duane Simmons video but I think if those 2 are not connected as above
your symptoms will happen as no 30V
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
> Regarging the wires by the old voltage regulator--- the 2 faston connectors on the "Twofer" must stay connected together and well taped up. The
> single wire gets disconnected and taped up on it's own. This is from memory from the Duane Simmons video but I think if those 2 are not connected as
> above your symptoms will happen as no 30V

That is also the way I remember it.
Ken B.

--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
I called Ron and left a voice mail with my phone number.

Ken B.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
I talked to Ron. He definitely knows what he is doing. I send him a couple of files. He may call me back later.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
Ken and John,

Thanks very much for your very clear suggestions and diagnostic guidance - much appreciated! I will visit the coach on my way home from work tomorrow
and try what you suggest, providing feedback afterwards.

Cheers,

Paul
Tucson, AZ
--
1976 Glenbrook with MAC dash, Alcoa wheels, Patterson carb, and A&E awning.
 
Thanks Ken, I really appreciate the effort. Just getting my coach ready
for summer traveil
Marcel in sunny New Mexico

> I called Ron and left a voice mail with my phone number.
>
> Ken B.
 
Ken and John,

I verified that the problem is not the oil pressure - disconnecting Pin 12 had no effect. Also, following your procedure, I verified the Onan runs
perfectly with Pins 5 and 9 jumped, and that there is ~30V across Pins 5 and 8 when running. So, looks like I need a new board.

Thanks again for your guidance!

Cheers,

Paul
--
Tucson, AZ
1976 Glenbrook with MAC dash, Alcoa wheels, Patterson carb, headers and A&E awning.
 
Jim b

> Ken and John,
>
> I verified that the problem is not the oil pressure - disconnecting Pin 12
> had no effect. Also, following your procedure, I verified the Onan runs
> perfectly with Pins 5 and 9 jumped, and that there is ~30V across Pins 5
> and 8 when running. So, looks like I need a new board.
>
> Thanks again for your guidance!
>
> Cheers,
>
> Paul
> --
> Tucson, AZ
> 1976 Glenbrook with MAC dash, Alcoa wheels, Patterson carb, headers and
> A&E awning.
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
http://bdub.net/gmcmotorhome.info/
Alternator Protection Cable
http://bdub.net/gmcmotorhome.info/APC.html
 
Try this?
http://gmc49ers.blogspot.com/2016/04/onan-start-relay-k1.html?m=1

>
> Jim b
>

>
>> Ken and John,
>>
>> I verified that the problem is not the oil pressure - disconnecting Pin
>> 12 had no effect. Also, following your procedure, I verified the Onan runs
>> perfectly with Pins 5 and 9 jumped, and that there is ~30V across Pins 5
>> and 8 when running. So, looks like I need a new board.
>>
>> Thanks again for your guidance!
>>
>> Cheers,
>>
>> Paul
>> --
>> Tucson, AZ
>> 1976 Glenbrook with MAC dash, Alcoa wheels, Patterson carb, headers and
>> A&E awning.
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
> --
> Gene Fisher -- 74-23,77PB/ore/ca
> “Give a man a fish; you have fed him for today --- give him a URL and
> -------
> http://bdub.net/gmcmotorhome.info/
> Alternator Protection Cable
> http://bdub.net/gmcmotorhome.info/APC.html
>
--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
http://bdub.net/gmcmotorhome.info/
Alternator Protection Cable
http://bdub.net/gmcmotorhome.info/APC.html
 
> Ken and John,
>
> I verified that the problem is not the oil pressure - disconnecting Pin 12 had no effect. Also, following your procedure, I verified the Onan runs
> perfectly with Pins 5 and 9 jumped, and that there is ~30V across Pins 5 and 8 when running. So, looks like I need a new board.
>
> Thanks again for your guidance!
>
> Cheers,
>
> Paul

Paul,

You may have burned a trace on the back of the board. Remove it and look at the back and if one of the traces is burned through, you can carefully
solder in a jumper wire to take it's place. I had a stupid attack and did something similar and found a burnt trace on mine. There were already
several jumper wires soldered onto the back of my board, so I added one more and haven't had a problem with it since. Although a new board might
still be in order, at least this might be a good diagnostic or even permanent fix.
--
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles,
Solar battery charging
 
Carl,

Thanks for the tip! I'll take a look at the back of the board.

Regards,

Paul

PS: Hope to catch up at the Bluegrass Festival rally.
--
Tucson, AZ
1976 Glenbrook with MAC dash, Alcoa wheels, Patterson carb, headers and A&E awning.
 
Yeah, we'll be there (Friday evening) See you then.
--
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles,
Solar battery charging
 
> Ken and John,
>
> I verified that the problem is not the oil pressure - disconnecting Pin 12 had no effect. Also, following your procedure, I verified the Onan runs
> perfectly with Pins 5 and 9 jumped, and that there is ~30V across Pins 5 and 8 when running. So, looks like I need a new board.
>
> Thanks again for your guidance!
>
> Cheers,
>
> Paul

Those are sometimes repairable. I use to repair them but I quit because I got tired of repairing them over and over again. A few that I repaired
stayed fixed. The circuit that is probably failing is the one that powers K2. It only has a few components on the board. There are a resistor, a
diode, and a capacitor. All are easily replaceable. Then there is the relay itself. It is not hard to replace EXCEPT that it is No Longer
Available. Finally there are the foil patterns on the back that may have deteriorated over the years and can be jumpered over with a wire.

After fixing many blown or deteriorated traces and components over the years I broke down and bought a new Dinosaur board. I plugged it in and never
had another problem.

Jim K. at Applied GMC has new Dino boards. I saw 2 or more of them of them on his table at the last GMCMI rally.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
Thanks Ken,

Indeed, I had already ordered a Dino board from Applied GMC, when Carl wrote suggesting I check for a burned trace on the bad OEM one. I'll keep the
old one as spare if it can be easily fixed.

Cheers,

Paul

--
Tucson, AZ
1976 Glenbrook with MAC dash, Alcoa wheels, Patterson carb, headers and A&E awning.
 
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GMCMI Fall 2026 Rally

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