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I don't use my XJ 600 so often and a few months ago, it wouldn't start due to an empty battery. The battery was old. I got a new one, and a SC10 "smart" charger to take good care of it.

Two weeks ago, I recharged the battery (charger in fully charged / maintenance mode) then used the motorcycle a few times until the other day the battery ended up empty again and I couldn't start at all.

I charged the battery to full charge (it took a few hours) and now the motorcycle starts again.

I'm trying to figure out which part is broken.


During those last two weeks, I noticed the speedometer light bulb didn't light and I figured it needed a replacement. Since the battery is charged, it lights again. I guess it was due to a low voltage battery.

The full battery has a voltage of about 13 V. Once I start the motorcycle, the voltage doesn't rise, even when I open the throttle up to 5000 rpm. From what I was told, this would indicate a faulty alternator.

I did a few tests (from this french webpage).

I opened the alternator and saw no obvious defect on the stator.

I unplugged the alternator to check the voltage at its connections. There is about 30 V between phases, going up to 60 V when opening the throttle. Those are approximate values but at least the 3 coils seem to behave the same.

I also checked each connector was not grounded and I measured the resistance of each coil at about 0.6 ohm.

From what I understand, this would indicate the alternator is fine and point at the regulator.

Is there any check I can perform to ensure the regulator is the broken part before I try to replace it?

Is there a fuse I'd need to check? (No idea, just asking.)

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From my own research, the tests reported in the question do point at the regulator.

I ordered a second-hand regulator with the same reference (SH640D-12) and since the replacement the voltage does rise up to 14 V when opening the throttle.

I consider the case close.


To anyone facing the same issue on the same motorcycle, the regulator is on the left side behind the small plastic fairing close to the tank (no need to remove the bigger one under the seat, only the screw closest to the front since it also holds the small fairing under it). Easy access. Easy replacement.

The stator connector used to test the alternator is on the right side, above the engine, under a small plastic/rubber protection. No need to remove anything.

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