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Start with checking condition of the (4) brushes. If worn down past about 1/2 they don’t charge right. Yamaha still sells them at $40 each, but there is a fellow on EBay Fromm Singapore who has them at 1/4 that price.
I cleaned up the brushes and the armature and believe the brushes are making good contact but are close to the limit marks so I ordered a set on ebay that may not be here for another 6 weeks. Still no charge. Bike starts and runs fine just not putting out any amperage. Any thoughts on what the problem might be given this?
I would test the regulator any way. It should charge even with the brushes at the line. Check the wiring at the stator, are the brushes good and loose in the channel, is the black wire grounded to the stator. These are problems I`ve found working on these in my shop.
When I tested the Dynamo it called for removing the green and the white wires and from the connectors and grounding the green side out and checking the voltage at the white terminal. This produced the .46 volts. Although it said to disconnect all the wires at the green and a white connectors I'm wondering if the small eye witb the light guage green wire that goes through the case and into the Dynamo coils I believe should have been left hooked up so basically power would go from the orange wire which is a field circuit and does have battery voltage with the key on, back through and out the green wire and then be grounded out to get a reading at the white terminal is this sound correct? I substituted a voltage regulator that I got from a salvage yard and it didn't make any difference.
Is the starter working?, it'd be unusual to have 'that' working & not charging as well even though i suppose the starting is reverse of what happens when it charges [another guess]. with the lid of the regulator you should see the cutout close--or close it by hang & see what happens. too many years ago for me [we sold AT1 electric starts in about "70 but sold more magneto models but of course they never played up except for brushes eventualy wearing out. Sooo--if you close the cutout with motor 'not running' 'i think' if you do it quick then the motor armature should give a slight kick--purely to prove if there's anybody home on that side of things. Someone will tell me off put me right but that's ok--just thinking how i'd go about it [smoke--so not that]. Test the continuity of your field coils & also the armature between segments & nothing to earth. Is the charging light on--on the dash & for that matter would a blown warning light stop the charging system--i think not. No blown fuses--only one main fuse by memory. Have seen BATTERIES in back to front--or charged back to front when they've been left for so long they don't know which way is what, so double check 'that' as DC systems don't SMOKE when connected in reverse--but won't charge. Good luck & sorry for yelling "Battery". Reading the story i'd say you're much more onto it than me!!. I just wait till everyone's run out of ideas & think what's left lol--cheating.