From www.justanswer.com/ythi
JustAnswer Customer: How can I test a voltage regulator on a Onan generator
Hank F.: Technician: Hello, my name is * * I am going to assist you with this.
Hank F.: Technician: What is the full model number of the genset?
JustAnswer Customer: 5.5 bqmfa1158h.
JustAnswer Customer: S/n.
JustAnswer Customer: # L990030946.
JustAnswer Customer: Marquis5500
Hank F.: Technician: To start, Find the voltage regulator mounted to the base pan of the set, directly behind the control box.
Hank F.: Technician: It is the aluminum box about 3" square with the 12 wires coming out of it.
Hank F.: Technician: The connector is actually inside the control box.
Hank F.: Technician: Remove the control panel.
Hank F.: Technician: Unplug the connector.
Hank F.: Technician: Set your meter to ohms.
Hank F.: Technician: Testing on the harness side of the plug, not the voltage regulator itself, ohm across pins J4-9 and J4-10.
Hank F.: Technician: It should read 20-30 ohms.
Hank F.: Technician: Next, we need to check the brushes and slip rings.
Hank F.: Technician: Remove the air cleaner.
Hank F.: Technician: Directly behind the air cleaner is the end bell of the generator.
Hank F.: Technician: In the middle of the end bell is a small plastic rectangular cover.
Hank F.: Technician: Use a flat tip screwdriver to pry the cover out and expose the brush block.
Hank F.: Technician: The brush block will have 2 round holes in it with a single uninsulated wire going through.
Hank F.: Technician: This is the brush lead.
Hank F.: Technician: Use a small probe or piece of small diameter stiff wire and push the probe through the hole until it touches the brush.
Hank F.: Technician: Mark the probe where it is flush with the brush block.
Hank F.: Technician: Remove the probe and measure from the mark to the end of the wire.
Hank F.: Technician: If it is more than 1", the brushes are worn out and must be replaced.
Hank F.: Technician: Remove the 2 screws securing the brush block, turning each screw 3-4 times each.
Hank F.: Technician: The brush block must come out straight, as it is made of ceramic and is very fragile.
Hank F.: Technician: Be careful not to drop the screws down into the end bell.
Hank F.: Technician: They are very difficult to retrieve.
Hank F.: Technician: Use the wires to help pull the brush block out.
Hank F.: Technician: Inspect the ends of the brushes.
Hank F.: Technician: They should be smooth and not cracked or chipped.
Hank F.: Technician: They should be worn into an even arch pattern.
Hank F.: Technician: They should slide freely into and out of the brush block.
Hank F.: Technician: If they stick or bind, clean the brush block with electrical contact cleaner.
Hank F.: Technician: Inspect the slip rings.
Hank F.: Technician: They are the 2 bands that the brushes ride on.
Hank F.: Technician: They are made of copper and should be as shiny as a new penny.
Hank F.: Technician: They should be smooth and have no pits or scratches.
Hank F.: Technician: If they are dirty, you can clean them by removing the spark plug wires and grounding them out.
Hank F.: Technician: (You do not want the engine to start when cleaning them).
Hank F.: Technician: Attach a piece of scotch brite to the end of a small stick.
Hank F.: Technician: Press the scotch brite against the rings and crank the set.
Hank F.: Technician: Do not crank for more than 15 seconds without stopping for a minute or two to let the starter cool.
Hank F.: Technician: When the rings are clean, ohm across them.
Hank F.: Technician: They should read 20-30 ohms.
Hank F.: Technician: If not, the rotor is bad and must be replaced.
Hank F.: Technician: If it is good, reinstall the brush block.
Hank F.: Technician: Reconnect the 12-pin connector at the voltage regulator.
Hank F.: Technician: Set your meter to VDC and connect the black probe to a good ground.
Hank F.: Technician: Insert the red probe into the back of the plug at wire J4-7 and press the start button.
Hank F.: Technician: It should read at least 10V.
Hank F.: Technician: Insert the red probe into the back of the plug at wire J4-9 and press start.
Hank F.: Technician: It should read at least 12V and climb as you hold start.
Hank F.: Technician: Insert the red probe into the plug at wire J4-10 and press start.
Hank F.: Technician: This voltage can vary from 1.5 - 20 volts, as long as there is voltage showing.
Hank F.: Technician: What are the results of these tests?
JustAnswer Customer: Generator motor will run but not put out any voltage.
JustAnswer Customer: I will check with you have give me and I will let you know how I make out thank you
Hank F.: Technician: The tests I gave you are the starting point.
Hank F.: Technician: They may pinpoint the problem right off, or we may have to do a couple other tests once we get these results.
JustAnswer Customer: Ok.
JustAnswer Customer: I get back with soon results