Home » Public Forums » GMCnet » Onan's revenge (Burned some stuff up...Why?)
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| Re: [GMCnet] Onan's revenge [message #281796 is a reply to message #281792] |
Fri, 10 July 2015 05:54   |
Jim Miller
Messages: 501
Registered: March 2008
Karma: 10
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On Jul 10, 2015, at 1:46 AM, Terry wrote:
>
> Anybody recognize whether this is the original board or not? Looks just like the one in the manual. I plan to repair it.
> http://www.gmcmhphotos.com/photos/onan/p58398-onan.html
From your pictures it looks like F1 might have a much larger ampacity than the 5 amp fuse that is supposed to be in there.
I would be looking for wiring harness shorts to ground and shorted caps. Either one of these can cause excessive current flow through the diodes which a properly sized F1 would have protected against.
For instance, look at the path F1/K2/CR7/pin 6 which feeds the Hobbs meter in the cabin - a short in that wire somewhere between the Onan and the Hobbs would cause excessive current through CR7.
Also F1/K2/R3/C3/S2 - if C3 is shorted then you might have excessive current through CR7. Caps are a notorious source of failure in 40 year old electronics and one of their favorite failure modes is to go shorted.
Those are just a couple ideas..but with a 40 year old board there could be many other component-related causes.
Although I have the ability to repair these boards - I don’t. I toss them aside and replace them with the much better designed and newly manufactured dinosaur board. Two of its main features are the full conformal coating to prevent corrosion and vibration of components not to mention that the components are of new manufacture.
--Jim "saving the lives of Onans...one unit at a time" Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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| Re: [GMCnet] Onan's revenge [message #281806 is a reply to message #281796] |
Fri, 10 July 2015 08:21 |
Mr ERFisher
Messages: 7117
Registered: August 2005
Karma: 2
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Senior Member |
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On Friday, July 10, 2015, Jim Miller wrote:
> On Jul 10, 2015, at 1:46 AM, Terry
> wrote:
>>
>> Anybody recognize whether this is the original board or not? Looks just
> like the one in the manual. I plan to repair it.
>> http://www.gmcmhphotos.com/photos/onan/p58398-onan.html
>
> From your pictures it looks like F1 might have a much larger ampacity than
> the 5 amp fuse that is supposed to be in there.
>
> I would be looking for wiring harness shorts to ground and shorted caps.
> Either one of these can cause excessive current flow through the diodes
> which a properly sized F1 would have protected against.
>
> For instance, look at the path F1/K2/CR7/pin 6 which feeds the Hobbs meter
> in the cabin - a short in that wire somewhere between the Onan and the
> Hobbs would cause excessive current through CR7.
>
> Also F1/K2/R3/C3/S2 - if C3 is shorted then you might have excessive
> current through CR7. Caps are a notorious source of failure in 40 year old
> electronics and one of their favorite failure modes is to go shorted.
>
> Those are just a couple ideas..but with a 40 year old board there could be
> many other component-related causes.
>
> Although I have the ability to repair these boards - I don’t. I toss them
> aside and replace them with the much better designed and newly manufactured
> dinosaur board. Two of its main features are the full conformal coating to
> prevent corrosion and vibration of components not to mention that the
> components are of new manufacture.
Yes so do I..
Also want to get rid of the tabs on the boards
>
> --Jim "saving the lives of Onans...one unit at a time" Miller
Love your tag line
> 1977 Eleganza II
> 1977 Royale
> Hamilton, OH
>
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--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html
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| Re: Onan's revenge [message #281807 is a reply to message #281792] |
Fri, 10 July 2015 09:08 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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If OEM it will have ONAN on the solder side. My unit is out on the hoist now for PO wiring clean up in the compartment. The tape on the + cable junction to eliminate the standoff was aged out. Also some grometts not seated. Jim can you give a quick how to on brush inspection and replacement. The service manual gives little detail. Also someone had not routed the pionts wire in the slot so cover was pinching and ready to ground. Amazing this thing worked fine with what I found. Just some things to inspect while you are in there.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Onan's revenge [message #281813 is a reply to message #281796] |
Fri, 10 July 2015 11:06 |
Bullitthead
Messages: 1411
Registered: November 2013
Karma: 5
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Thanks Jim, I will be checking those components when I repair the obvious damage. I never checked the capacity of that fuse, just made sure it was not blown when Onan wouldn't start. Don't have the necessary funds for a new board, but I do have the parts to fix the old one. However, I don't have the K1 relay, which is different than the usual Ford-type starter relay. I know of no Fords using ground to trigger a common-positive relay, so I'll have to invent one if I can't find it at a reasonable price. Has anybody ever substituted a 40 amp Bosch-type relay for K1?
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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| Re: [GMCnet] Onan's revenge [message #281814 is a reply to message #281813] |
Fri, 10 July 2015 11:19 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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One thing I do know for sure about ONAN Generators. Never shut them down
when there is any kind of a load on them. And for sure, do not remove your
finger from the stop button until all sounds have ceased from it. That will
make your Bridge Rectifier much happier, particularly if it is an original
equipment one.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Fri, Jul 10, 2015 at 9:06 AM, Terry wrote:
> Thanks Jim, I will be checking those components when I repair the obvious
> damage. I never checked the capacity of that fuse, just made sure it was not
> blown when Onan wouldn't start. Don't have the necessary funds for a new
> board, but I do have the parts to fix the old one. However, I don't have the
> K1 relay, which is different than the usual Ford-type starter relay. I
> know of no Fords using ground to trigger a common-positive relay, so I'll
> have
> to invent one if I can't find it at a reasonable price. Has anybody ever
> substituted a 40 amp Bosch-type relay for K1?
> --
> Terry Kelpien
> ASE Master Technician
> 73 Glacier 260
> Smithfield, Va.
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: [GMCnet] Onan's revenge [message #281886 is a reply to message #281868] |
Sat, 11 July 2015 18:52 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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When Duane Simmons was rebuilding the original boards, they were OK, then
towards the end we were having problems with the board rely so much that we
started using the Dyna sorce units.
I love the ones for the 76-78 ones as they have the pig tail so one does
not need to mess with all the individual connections.
On Sat, Jul 11, 2015 at 7:49 AM, Matt Colie wrote:
> Jim,
>
> I know you well enough to have to believe you, but you say the Dinosaur
> board is a better design.
> Do you mean a better circuit design?
> Or just newer and better materials and components?
>
> At the moment mine is good again, but I went three rounds the molex in
> 90°+ a night ago.
> Do you have a plan to improve the reliability of those?? (I avoid them in
> the things that I build.)
>
> Matt
>
> Jim Miller wrote on Fri, 10 July 2015 06:54
>>
>> Although I have the ability to repair these boards - I don't. I toss
> them aside and replace them with the much better designed and newly
>> manufactured dinosaur board. Two of its main features are the full
> conformal coating to prevent corrosion and vibration of components not to
> mention
>> that the components are of new manufacture.
>>
>> --Jim "saving the lives of Onans...one unit at a time" Miller
>
>
> --
> Matt & Mary Colie - Members GMCMI, GMCES
> '73 Glacier 23 - Still Loving OE Rear Drum Brake with Applied Control Arms
> SE Michigan - Twixt A2 and Detroit
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--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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www.appliedgmc.com
1-800-752-7502
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| Re: [GMCnet] Onan's revenge [message #281905 is a reply to message #281868] |
Sat, 11 July 2015 21:20 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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I fixed more of those boards then I want to talk about. Some of them I fixed more than twice. I gave up fixing them and went with the dinosaur boards.
George Zookoof (he is going to kill me for mis-spelling his last name) had a problem with his Dinosaur board. He got them to make a one resistor change. They did and sent him a redesigned one. As far as I can tell they never implemented that change on the ones they are making today. Contact George for more details.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Onan's revenge [message #282035 is a reply to message #281807] |
Mon, 13 July 2015 18:23 |
Jim Miller
Messages: 501
Registered: March 2008
Karma: 10
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Senior Member |
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> On Jul 10, 2015, at 10:08 AM, John R.Lebetski wrote:
>
> Jim can you give a quick how to on brush inspection and replacement.
Hi John,
I’ve not seen any Onans with brush problems and that includes machines with 500 hours or more on them. I also don’t see a lot of opportunity for them to get damaged or worn out unless a unit has thousands of hours on it. It is, however, possible to break the brushes if someone has tried removing and then re-installing the generator end-bell without removing the brush holders from their mount.
in any case if you want to inspect your brushes then remove the plastic grilles from the end bell vents, remove the two hex-head bolts from the brush holder and raise the holder up where you can see the brushes to make sure they have plenty of “meat” left on them and they aren’t cracked or otherwise damaged. There are two brush holders in the unit so you’ll have to repeat the procedure for the other one. This procedure is tricky due to the minimal amount of access available through the end bell and I wouldn’t recommend it unless you have seen sparking at the commutator when running under load or if you suspect the brushes are part of some other extant problem.
If you have the end bell off for some other reason (bearing replacement, field replacement or to service the commutator rings) then the brushes will be easily available for inspection. Just make sure both holders are up and out of the way before you put the bell back on.
--Jim "saving the lives of Onans...one unit at a time" Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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| Re: [GMCnet] Onan's revenge [message #282036 is a reply to message #281868] |
Mon, 13 July 2015 18:35 |
Jim Miller
Messages: 501
Registered: March 2008
Karma: 10
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Senior Member |
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On Jul 11, 2015, at 10:49 AM, Matt Colie wrote:
>
> I know you well enough to have to believe you, but you say the Dinosaur board is a better design. Do you mean a better circuit design? Or just newer and better materials and components?
HI Matt,
I have not audited the circuit to see if they made any changes to it. I like the board because it has better conformal coating, has pigtails directly soldered on instead of spade lugs and most of all it has brand new components.
Over the years I’ve fixed many pieces of HP laboratory equipment of 1970’s to 1990’s vintage. This gear was originally built to the highest standards with the highest quality components and spent its life in controlled lab environments - yet the predominant cause of failures are components that go out of spec due to age. Capacitors are the #1 failure item that I see…they go shorted. They go open. Their series resistance changes over time. The Onan board lives a much more hostile life in extremes of temperature and humidity and therefore I immediately suspect component failures when someone has a problem with one. All the time taken to clean up the board, troubleshoot it, replace the bad component(s) and re-test it leaves you only with a 40 year old board that will work long enough for the next component to go bad. As others have pointed out..they aren’t worth fooling with.
> At the moment mine is good again, but I went three rounds the molex in 90°+ a night ago. Do you have a plan to improve the reliability of those??
I’ve not had too much trouble with Molex connectors in my career as long as they were assembled with the proper tooling and real Molex pins. I can say, though, that I found a problem on one Dino board where one of the pins would not latch in the connector body and would vibrate itself out over time. The fix for that is easy…spread the tangs on the pin slightly and stick it back in the hole.
--Jim "saving the lives of Onans...one unit at a time" Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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| Re: Onan's revenge [message #282041 is a reply to message #281792] |
Mon, 13 July 2015 19:23 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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Thanks Jim. I reinstalled the unit yesterday and just saw your post. I had removed the 4 plastic grills to blow out dirt whilst on the hook. It's a light wave black hole in there so I left the brushes alone as no AC issues. I've done brushes on Delco alternators etc with the spray straw keeper trick but best if I see one apart first so I know how it goes back. Mine ran fine though I found a burnt trace and carbonized area along with some kindergarden grade PO work I had to clean up. Got a pile of wire and crimps from what I undid in the interest of fire safety. Remote cable now is run in covoluted self extinguishing tubing the right way and batt cables resecured and rerouted. Those plastic strain reliefs will test you but used a heater hose clamp to compress while pushing in place. Some slit hose over possible chafe areas for insurance. Spent 2 hours putting tools away afterwards and cleaning up so fairly involved project, but now it will be much easier for future service without the pound of dirt/oil/cement I putty knifed off the tray.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Onan's revenge [message #282708 is a reply to message #281911] |
Tue, 21 July 2015 13:45 |
Bullitthead
Messages: 1411
Registered: November 2013
Karma: 5
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Senior Member |
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Well, I was able to buy groceries after all, but it required another trip around the Onan tree...
Repaired the board and fabbed up a relay setup to take the place of that common-feed double pole single throw insulated K1 relay. I used a sealed Bosch-format relay to power the relay on the starter, and used that relay's positive output to trigger another relay to connect power to the K1-I wire going to the board and the electric choke. This immediately burned my fuse that I used to power the K1-I relay, and had no effect on the board or the NEW 5 amp fuse on it. Measuring the load on the relay connections showed me the board was not causing the problem, it was the choke motor(E1). Only 1.7 ohms through that thing, so almost 7 amps was being pulled out of the K1-I circuit. Moving the terminal on the choke resulted in erratic resistances from shorted to open and everything in between. Took the wire off the choke and put an insulated connector on the end (the fork on there was just hanging on by a few strands)and strapped it out of the way for storage. I'll work on the choke motor later,...maybe when it's not a hundred degrees outside  .
Onan started right up after replacing my extra fuse and ran for about a half hour with no problems, but when I shut it down it kinda had a rattling sound like a rod bearing was loose (running at no load), so all may be in vain 
Thanks everyone for the help!
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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