Charging Problems....

So I have a 1983 XJ750 that will not charge no matter what I throw at it. I have replaced every component save two, the carbon brushes (that are clean and in spec.) and the alternating rotor. My rotor measures three ohms which I understand is below spec. but damn I am getting Nothing at the battery. Does anyone have a source for a NEW alternating rotor I can buy and put this bike back on the road? My e-mail is batardpaiens@gmail.com and my cell number is 1-904-534-7220.

 

Have you checked all the ground connections? Delete your personal info (trolls roam here) and start a conversation with Chacal (Len); he's our parts guru.

Gary H.

 

did you use an eraser to clean the surfaces where the brushes make contact
there are 2 parts to the alternator
rotor and stator

also you will need to test the voltage regulator and clean all connections

download this set of manuals

haynes 650-750 free down load
http://www.manualslib.com/manual/837861/Yamaha-Xj750.html

 

page216 of haynes

 

Check the connections where the alternator plugs into the regulator/rectifier (three white wires, plus a black, a brown, a green, and a red) under the left side cover. These connections tend to oxidize, heat up, and melt the connector (as well as losing contact). Clean or replace them if they show signs of oxidation or melting. This is a common cause of charging problems in these bikes.

 

Thanks for the good advice guys! I have a simplified the wiring harness and the grounds are solid. I am just not getting any voltage from the three white wires. I believe I simply need a good rotor as mine is below spec. I will hit up Chacal and see if I can get a good one.

 

Did you three phase test it? Just asking.

Gary H.

 

You did check on AC when checking for voltage on those wires, right?

 

rotor, stator, one spins one don't. can something really go wrong with the rotor?

 

The laquer on the rotor coils can fail from heat or age and cause a short, or cause the wire to corrode through.

 

yes i did check for AC voltage

 

I always like to cut that connector off.

This is worth doing even if your charging system is working. (in my opinion, some may not agree)
First, test the voltage at the battery when the bike is running.
Second, cut off both ends of the connector.
Third, splice and solder the wires together then heat shrink or tape the wires. (make certain you keep each wire separate from the others)
Fourth, recheck battery voltage with the motor running.
I bet you'll see an improvement.

Toolman

 

If there's no AC voltage between any two of the three white wires, the problem pretty much has to be in the field coil. If the field coil (Brown to Green) measures in-spec from the connector, and is getting 12V or so when running, then something is missing in your test process. If it measures in-spec, but is not getting much (DC) voltage between Green and Brown, then you probably have a bad regulator.

 

Any luck on this? The 3 ohms on the field coil does seem like the problem so either a good used one or rebuilt one would be good advice.

I am local (Jacksonville) and have a little bit of electrical experience if you get stuck. I also have the tools for removing the field coil and a spare used field coil that you would be welcomed to borrow if needed.

If the measurements of 3 ohms are accurate on the field coil, I would suggest not hooking another regulator up to it until the field coil is replaced. I have no idea what the maximum current rating is on the regulator, but it might be possible to damage the regulator with low ohms on the field coil before blowing the ignition fuse.

 

Can't hurt any doing this.

 

Eliminating the connector does make some other repairs a bit more difficult. I'd reccomend replacing it with a new, waterproof connector to eliminate the oxidation buildup that leads to the wires burning.

 

anything is better than stock