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Hank F.
Hank F., Technician
Category: Small Engine
Satisfied Customers: 14730
Experience:  Certified on Onan and Generac generators
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I have a mitsubishi mge 5800 generator. The engine starts fine

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I have a mitsubishi mge 5800 generator. The engine starts fine and runs good, but does not generate power. The power will either go to 120 V briefly, or not start at all. I just changed the brushes, this did not help. The generator is about 5 years old and has about 300 hours of light usage. Any help greatly appreciated.

Hello,

Do you have a good multi meter available?

 

I have a service manual for this unti, which is very detailed. I can upload it for you if you wish, or I can walk you through the steps for troubleshooting. Just let me know.

 

The most likely problem is a bad voltage regulator.

Customer: replied 7 years ago.
Yes, I have a good multi-meter. I have the basic operating manual, I don't know what I am looking for.

OK, I am going to go on the assumption that it is a bad voltage regulator. I am going ot give you a series of tests, and what the normal results of those tests should be. At any time you get a result significantly different than what it should be, stop and let me know. We are actually going to test all components to make sure they are good. I do not like changing parts unless I know they are bad.

 

First, remove the brush cover. disconnect the wires going to the brush leads and ohm across the brushes. You should get 6-7 ohms.

Place one meter lead to one of the brush leads, and the other meter lead to the frame of the set. You should get no continuity.

Reconnect the wires and set your meter to VDC. Place one probe of the meter to each brush lead and start the set. You should get 12-20VDC. Stop the set. Disconnect the wires again.

Remove the control panel and locate the voltage regulator at the back of the control box. It will have a 6 wire connector with the wires being red, white, brown, light green, and 2 yellows. Unplug this connector.

If you have electric start, you can use the battery on the set. If you have a manual start, you will need a 12V battery. Make up 2 jumper wires about 3ft long, and attach a connector the same size as the spades on the brush leads to one end of each wire. The brown wire is the positive brush, and the light green wire is the negative brush. Attach one of the jumpers to the positive brush and the positive post of the battery. Attach the other wire to the negative brush. Start the set and attach the wire from the negative brush to the negative terminal of the battery.

Go back to the 6 pin plug that you just removed from the voltage regulator. Set your meter to VAC and connect the leads across the following pairs of wires:

 

BE CAREFUL. THERE WILL BE LIVE VOLTAGE PRESENT AT THE PLUG.

 

Red to white should be 110-126V.

White to light green should be 122-142V.

 

If these all check OK, your voltage regulator is bad.

Please let me know what you find.

Customer: replied 7 years ago.
Sorry for the delay, I ran the checks you suggested.

The brushes are reading about 10 ohm (I checked between runs was 10.2,7.5,10)
Brush to frame was 135 megaohm... no continuity.
With the wires connected my meter was reading -1.3V DC with the negative lead on the green brush.
The connector from the AVR had four wires in the connector, the two yellows were separate, I only unplugged the four.
White to lt green was 114VAC
Red to white was 110VAC
The battery I was using wasn't fully charged (12.3V)


No problem, it is a busy time of year for everyone.

 

With the tests you ran, the results are consistent with a low battery. By manually exciting the field (jumping the 12V), we have proven that the rotor and stator windings are good. The set will produce electricity when voltage is applied to the brushes. The problem is that the voltage going to the voltage regulator is not being rectified to DC to excite the field, so that means the voltage regulator is bad. Replace the voltage regulator and you should be good to go.

 

You will be able to order one directly from Mitsubishi.

For Parts and Service, please contact Mitsubishi Engine North America, Inc
Ph(NNN) NNN-NNNNFax(NNN) NNN-NNNN/p>

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