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'80 cb750k Charging system troubles

nickajeglin

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So, the new bike isn't charging.

I checked the stator, all three leads continuity to all the other leads.
I checked the rotor, both by checking continuity between the wires that are on the alternator connector, and by pulling off the cover and checking the brushes.
Is it true that the rotor in this bike isn't a permanent magnet, but has a field excited in the windings by those brushes?
Since both of these checked out ok, I moved on to the regulator/rectifier.

Continuity between all the yellow wires, and green one way, but not the other.
Continuity between all the yellow wires, and red/white the opposite way, but not the other.
My small ability to read schematics tells me that this is how it should be, is that correct?

All the connections look great, but since I don't have an ammeter I can't really check like the manual says, by hooking one up in series.

I put a voltmeter across the battery terminals though, and reved it a bit, and there wasn't really any response, all the way up to 5000 rpms. So I'm assuming that means that something is bad on the charging system. (plus.... the battery dies after a while of riding, so that's a red flag.)

Now that I'm away from the bike and thinking a little more systematically, I'm realizing that whatever is sending an excitation current off to the rotor could be malfunctioning, which would make the alternator not work.

Now wait, maybe I'm backwards here..... Does the rotor get an induced magnetic field, which is transfered to the stator, which then charges the battery, or is the stator induced, the rotor picks it up, and then charges the battery? It has to be the first, right? That's why the three phase yellow wires go to the rectifier. rather than the wires from the brushes.

Grr. I don't so much love electrical problems.

Thoughts on what I may be missing? I'm pretty inexperienced, so I often miss stupid simple things.
 
Ok, I've been fighting this all day, but I think I found it. The two copper contact rings on the rotor had connectivity, so I assumed they were ok, but it seems that they actually should show ~4 ohms of resistance, and mine only reads ~.01 ohms, I think that this implies an internal short in the rotor. I've got a friend with a pretty badly crashed cb750, so I'm going to go check out the rotor tonight, may be that it will be good. Otherwise, ebay here I come.
 
I was going to say check between the rings on the rotor.

Check out bikeboneyard.com, I just bought a stator cover from them, $35. Most wanted 40-70, I'd use them again in a heartbeat.

On our bikes it's a common problem, charging system that is. I found out on here that if your regulator/rectifier goes it could quite pissibly mean you need a new stator.
 
I would like to know what you find out. I have a 79 that tonight decided it was going to no longer charge the battery and left me on the side of the road for a while.
 
check the field coil wires. i had an issue where one of the field coil connections had come loose. resoldering it fixed it right up. before that I was getting an intermittent charging issue (the headlight wouldn't brighten with revving the engine).
 
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