Topic: 78 CB750F - Charging Issues.

[therager]

I've had this bike for a long time and work has kept me away from this project, now im back at it and having the same old charging issues that have plagued this poor bike since I bought it several years ago.

I've done a fair amount of research and performed the following tests for the rotor/stator:

RESISTANCE: (Unplugged the rotor and stator and measured the lead resistance)
Rotor: 8 Ohms between white and black leads. (seems a bit high from the ~4 Ohms i've read it should be)
Stator: 0.7 Ohms per yellow wire pair, no shorts to ground.

VOLTAGE: Bike running at around 3000 RPM
Rotor: DC voltage on leads ~ 12V
Stator: AC voltage ~ 12VAC between any yellow wire pair, ~9VAC between yellow wire and ground.

It seems like the AC voltage is very low. From what I've read on the forums, it should be somewhere in the 50VAC range. Is this correct?

I am still getting around 12.4 volts on the battery, independent of the RPM. If I unplug the headlamp though, I get a proper ramp up to 14V on the battery as I go from 0 to 3000RPM.

Any ideas of what the problem could be?
Thanks in advance.

[surveywaters]

If unplugging the headlight allows proper charging then I would start with, as said by many people on here, cleaning all of the connections on the bike and applying dielectric grease to prevent the reformation of corrosion. A dirty connection acts as a resistor and many resistors inline can cauce significant voltage drop.

[therager]

If there is a current leak somewhere, that would explain the inability to charge properly, but shouldn't the voltage on the AC leads of the stator be 50VAC regardless?

[Jerry Rxman Griffin aka MuthaF'er]

The rotor is a big chunk of metal and it carries no voltage. Field coil perhaps?

Stator output is dependent on the voltage regulator supplying the proper current to the field coil. If field coil and stator have correct resistance and voltage regulator is working properly then the AC output should be fine. I'll assume your rectifier is working properly since you can get 14V with the headlight unplugged? Pull your headlight fuse vs bulb and take the reading.

[Thousandson]

Watch this video, he might be a little crazy, but it is one of the best out there. Grab your muilti meter, and you can start checking wires.


HONDA cb750 charging system explained

[therager]

I'll on the road again for several days but i'll measure as soon as I get back.
Thanks for the ideas.

[bruzer59]

 hi ,listen when it comes to the stator & the field coil on the cb750 YOU MUST have a fully charged battery ..

[2wheels]

I would check the 2 white multi pin connectors down behind the side cover.  Mine looked not bad but the crimp joints had overheated and were causing problems for me.  I cut the wire back a bit and soldered the wire to the connector pins.

As for the AC measurements, some multimeters are meant to measure 60 Hz like what comes out of your home AC plug.  Your bike is spinning at 3000 RPM so the frequency you are measuring is at least 3000 Hz.  Your meter may not like that and give you inaccurate readings.  Or maybe something is failed so this is just something to keep in mind.

[Xnavylfr]

HERE!!!  http://www.hondachopper.com/garage/troubleshooting_charging_system/troubleshooting_charging_system.pdf



Xnavylfr(CHUCK)