I have searched RVForum and have not found my particular problem listed. I have a 2000 Onan 4000 MicroQuiet "KY" version J mounted in a 2000 Fleetwood 26' Tioga Class C. The generator has been running and outputing fine for the few months I have had it. During its last use, it just stopped running, and at the same time I could smell a sweet/electrical burning scent in the coach. I tried to restart it but it would only run for a moment and then quit. The flashing code is 27, "Controller unable to sense output voltage".
I am pretty sure fuel and oil are not the issue, checked both, including the low oil sensor, they are fine. Fuel pump outputs fine. Besides, the code 27 points to an electronic problem.
I checked the AC voltage at an outlet in the coach while trying to start the generator and it would climb to about 50v before the engine would quit. I again smelled the slightly sweet electrical burning smell (not insulation, something else) and found it was coming from the AC to DC converter. I removed the converter and tried it in the garage and promptly blew up a power strip! I opened up the converter and found a large (200v, 820uf) axial lead can type capacitor blown up. I am pretty sure this was the source of the smell. I replaced the capacitor (good ol' eBay, $13 shipped for two of them, arrived in two days) and the converter now works fine. I have left the converter out of the RV while I try to isolate the generator problem.
So it would appear the generator suddenly lost its ability to control the output voltage, outputed mucho volts, fried the converter and probably its control PC board. I have a repair manual on order from Onan but have not received it yet, but it sounds to me like the voltage regulator (which is apparently incorporated into the control PC board) has failed. It would seem the "J" and newer models don't have a separate voltage regulator (or if they do I can't find it), it is built into a flat 5" square PC board that is sealed in a flat open top 1/2" deep tray with clear epoxy, then bolted onto a subframe that lives in the bottom left front of the generator. It has a large heat sink sticking out the middle. Until I get the repair manual I am thinking the control PC board has failed, but I don't know enough about Onan generators to know if there might be something else (brushes, stator?) that might have caused the control PC board to fail, if indeed it has. Anyone have any ideas?
Tom Duncan
I am pretty sure fuel and oil are not the issue, checked both, including the low oil sensor, they are fine. Fuel pump outputs fine. Besides, the code 27 points to an electronic problem.
I checked the AC voltage at an outlet in the coach while trying to start the generator and it would climb to about 50v before the engine would quit. I again smelled the slightly sweet electrical burning smell (not insulation, something else) and found it was coming from the AC to DC converter. I removed the converter and tried it in the garage and promptly blew up a power strip! I opened up the converter and found a large (200v, 820uf) axial lead can type capacitor blown up. I am pretty sure this was the source of the smell. I replaced the capacitor (good ol' eBay, $13 shipped for two of them, arrived in two days) and the converter now works fine. I have left the converter out of the RV while I try to isolate the generator problem.
So it would appear the generator suddenly lost its ability to control the output voltage, outputed mucho volts, fried the converter and probably its control PC board. I have a repair manual on order from Onan but have not received it yet, but it sounds to me like the voltage regulator (which is apparently incorporated into the control PC board) has failed. It would seem the "J" and newer models don't have a separate voltage regulator (or if they do I can't find it), it is built into a flat 5" square PC board that is sealed in a flat open top 1/2" deep tray with clear epoxy, then bolted onto a subframe that lives in the bottom left front of the generator. It has a large heat sink sticking out the middle. Until I get the repair manual I am thinking the control PC board has failed, but I don't know enough about Onan generators to know if there might be something else (brushes, stator?) that might have caused the control PC board to fail, if indeed it has. Anyone have any ideas?
Tom Duncan
