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I have just picked up a CB750 C and within a week of riding it around the charging system has called it quits...
I have narrowed it down to the rotor as the first part I will replace, I believe the R/R is also toast though.
Looking around I have found there is a permenant magnet conversion for the XS, is there one for the CB as well?
Those that have replaced their rotors and R/R's have you had any repeat offenses? I am hoping that this system is the original and that I only have to do this once. I typically ride 100km/day and need it to be reliable.
There used to be a web page by Mike Nixon to troubleshoot the DOHC charging system but all I can find now is the book he sells.
The factory manual which you can down load also has a step by step fault finding process. From memory the rotor should be between 2 and 5 Ohms you need push the meter probes in very hard to get a good contact and accurate reading. There should be no short to ground from any of the 3 fields coil connection. There is a way to disconnect the reg / rec each side so you can test AC volts in and Dc volts out but I cant find it on this pc so may be on my work pc.
I like the idea of the mosfet regulator, it means I would need to install a separate rectifier though. I have read about some folks using an old dodge one but it looks a little big... mtf.
the 750 uses a field excited alternator, not a PM. In addition, the alternator has brushes and conductive rings for the brushes. the problems, solutions for a permanent magnet alternator don't apply for field excited alternators. Different animal.
Lack of charging can just be worn out brushes, or dirty rings on the rotor.
You should always trouble shoot, check condition of parts. A new regulator will not fix worn out brushes, and you may kill the new regulator.
One thing Honda did on my 91 NH750 is created a field excited alternator with no brushes. The field coil is stationary, inside the rotor. The rotor turns, but without brushes, they eliminated the mechanical wearing part.
Part of my issue was the test leads I had purchased from Princess Auto came with some built in resistance! Changing them out for some more expensive ones improved the readings to the point where I was able to identify a bad rotor and regulator. I also found that the rotor and regulator from my parts bike was still good!
Thanks Sonreir and Notlob for the great troubleshooting tips.
Also, if you haven't tried the rear axle rotor puller trick, it works just dandy!
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