Voltage Regulator Failure?

Hi,

I have a 1982 XJ750J Maxim.

Been working on it over the winter, thanks for the answers to my carb issues in the past. It has run like a dream. Got it out and working but ran into an electrical gremlin.

3rd day of using it, it left me stranded at a gas station. Just stalled and lost all power when I went to pull out. Jumped it and was able to make it halfway home - just shut off white riding, jumped again and got it home. Ran fine the rest of the day. I did notice the idle kept going up and down oddly, like sometimes fine then randomly drop - adjust and then it would randomly go too high.

Everything below I followed the shop manual and other threads.

I dove into the electrical system more to check out why the battery must have died. I was idling at 12.8v and only going up to 13.4 at like 5k rpm, so well under the spec. I dove deeper. Found the 3 white wire connector from the alternator to the RR was melted and smoked. I cut out the connector and replaced the ends with spade heat shrink connectors. No change in the voltage.

I then checked the brushes, they appeared within spec but ordered new ones since they did look worn down. Stator slip plate showed 5.2 ohms across surfaces. I installed them a couple days ago, cleaned the inside and its all shiny and smooth.

Checked the white AC wires leading into the regulator - now this 8 pin connector is pretty burnt so I once again cut it out and redid the connections. At idle I am getting 19 VAC and then up to over 65 VAC when revved, across all wires. But only when I disconnect the red wire, when its connected it the white wires wont go over 11 VAC. But here's where the plot thickness. Its gotta be something with load, because when I disconnect the red wire the idle goes up and as soon as its powered on it drops down. It runs flawless without the red wire connected, when I connect it - it feels like its under a load. Like when you turn the AC on in your car if that makes sense.

After doing all the this testing with the bike running I noticed the headlight kept brightening. I checked the DC at the battery. At idle was 13v, hmm higher than before, but when revving it went up to 14, 15, 16, 17 VDC, I shut the bike off after that, only to start when I check voltages again, as I know I risk damaging stuff.

I checked the signal wires and they are also within spec to the alternator brushes. They are the green and brown wires. I checked the diodes and they are between 578-600 mVDC across all white wires in 1 direction and OL on the other directions.

I think the RR died on me and left me stranded and is now overcharging when it gets hot. LIKE SUPER HOT. Any other suggestions? I bought a CALTRIC off eBay and it just didn't work - like plugged in and nothing. They are sending a replacement as it might have been defective. I also ordered a used/tested one off eBay, maybe with it being so old the newer replacements don't have the tolerance/threshold of voltage. That should be in, in a couple days.

Does anyone else have any other opinions?

Notes,
Yes does not have the original fuse box, has blade fuses.
Battery is only a couple months old. Sealed AGM battery.
All lights and ATARI work - including the fuel sender believe it or not. (I discovered the one white wire needs to be connected for to trigger the display).
It was running fine when I worked on it in the walk in basement, but I did keep it on a charger so may have never noticed the voltage issues - sadly didn't even check it until it left me stranded.

Thanks in advance.

 

Sounds like you might have found the issue. At 3k rpm you should be around 14vdc, anything in the 15 or higher range and it will cook your battery. So, you said you have a good battery, you might not after your last ride that left you stranded on the road.

While you are waiting, I would go through all the connections on the bike. One at a time and just inspect, clean and dielectric grease on them just to make sure. The melted and warn plastic is found not just on the XJ bikes but most metric bikes in general.

Not sure if you have a manual yet? If not get one. It would be a great help for you to post some pics along with your written description of your troubleshooting.