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XS650SG Alternator wanted

Discussion in 'The Garage' started by Dangermouse, Feb 13, 2020.

  1. Team Junk

    Team Junk XS650 Addict XS650.com Supporter Top Contributor

    Just a couple of items of note here.
    1) Your bike was probably built in the fall of 79 as one of the first 1980 models.

    2) What kinda shape is your battery? Have you charged it off the bike and what voltage do you get with it fully charged disconnected from the bike? You should have full battery voltage on one of the brushes.

    3) Check both the stator and charge coil resistances with a good VOM and compare specs.

    4) Not sure which fuse box you have but the glass fuse boxes are notorious for crumbling and falling apart.

    5) To test the key switch, jumper from red to brown on the key switch connector in the headlight bucket and see what voltage you get on the brushes.

    Keep us posted.
    Jim likes this.
  2. Team Junk

    Team Junk XS650 Addict XS650.com Supporter Top Contributor

    Looked at partzilla and yes it appears you have the glass fuses. Weak spot. Would be my first thing to check after battery condition.

    Really like the frame color on your bike. Stands out nicely.

    gggGary and Jim like this.
  3. Thanks, replaced the fuse box with modern fuse box (bladed fuses) when I first got the bike as the old one was broken.
    New battery on bike holds its voltage well. No increase in voltage at the battery when rev bike.
    will get the garage guy to do all the checks on the troubleshooting page.
    The frame colour is what got me in on the bike as it is exactly the same colour as the XS I had back in 1982 only that was a 1976 bike.
    Jim likes this.
  4. Jim

    Jim Beyond the edge, is the unknown. Here be Dragons XS650.com Supporter Top Contributor

    Mine was registered in Oct of 79 as a 79SG... when it's actually an 80 model year SG. That's just the quirky way some states did it back in the day.
    gggGary likes this.
  5. Ah that's re assuring, over here we have 2 registrations a year, March and September. just to confuse matters
    Team Junk, gggGary and Jim like this.
  6. Team Junk

    Team Junk XS650 Addict XS650.com Supporter Top Contributor

    Has the bike been charging fine and suddenly stopped charging ?

    Try disconnecting the connector to the alternator and see if the voltage on the brown wire on the bike side of the connection increases. If it does then something in the charging system has shorted. Testing the resistance of the stator and charging coil will eliminate them.
    The diodes in the regulator can be tested on the 3 white wires on the regulator.
  7. Unfortunately always been like this since I got it last year. didn't do many miles last year and carried a spare battery. Bike was off the roads for 6 years, previous owner part restored then sold (now I know why!). Still it was a bargain.
  8. Bushyeyed1

    Bushyeyed1 Cafe Racer

    I have a spare tci alternator but let me double check the resistance to make sure it is within specified tolerance.
  9. Team Junk

    Team Junk XS650 Addict XS650.com Supporter Top Contributor

    You snagged a nice one.
    I think the 1980-83 models are the best.

    Suspension and brakes are as good as it got for the stock bikes.

    Solid state regulator that was used on quite a few later Yamaha models that is pretty easy to source.

    The TCI ignition was a great improvement that is fabulous right to the point when the igniter box smokes. I'm working on adapting another TCI box to it that would be easier to source.
  10. Cool. Thanks Bushyeyed, you guys seem to know your stuff, I am just starting on the classic route. Will do more DIY mechanics as my confidence grows, electrics still a dark art to me. Ride a Triumph 1200 Speedmaster as my usual ride, tour Europe etc. Love riding the Yam, Enjoyed tinkering with it in my shed over the winter.
    Put in new clutch, changed both oil filters , serviced the brakes, chaged the oil, (that was interesting, so many different views on here as to what oil.) Will be taking the bike to a few shows this year, the bike seems to make people smile when they see it.
    lakeview likes this.
  11. Team Junk

    Team Junk XS650 Addict XS650.com Supporter Top Contributor

    Your shed must be warmer than mine.
  12. Bushyeyed1

    Bushyeyed1 Cafe Racer

    The rotor brushes will need to be replaced but it checks out. Passed the stator coil, rotor coil, and pickup coil inspection resistance checks. PM me if you want it $50 usd plus shipping.
  13. Thanks Bushyeyed, have PM'd you I think......
    Thanks Junk....My shed is good in the winter, although our winters are mild, rarely goes below freezing. Rare to see snow on the east coast, salt air keeps it away.]
    Bushyeyed1 likes this.
  14. Jim

    Jim Beyond the edge, is the unknown. Here be Dragons XS650.com Supporter Top Contributor

    You have a thread goin' for that?
  15. Team Junk

    Team Junk XS650 Addict XS650.com Supporter Top Contributor

    Working on it. Have discussed it some on my old brown thread. Working on getting a scope going so I can see what is going on the pickup coils.

    Do have mine running on a XJ700 TCI. Just can't get it to advance. I suspect the shape of the magnet is not giving enough duration to the pulse.
    Jim likes this.
  16. 59Tebo

    59Tebo 59Tebo Top Contributor

    Welcome to the party, Cal!
    Stay tuned! There's a lot of really smart chaps on this forum! It makes me wonder, sometimes, why such talented people are messing around with old motorcycles. I've said before, I stand in the shadow of giants. (Actually, I stand around the corner from the shadow of giants... :doh:) You've had other motorcycles, so you're aware the importance of having a manual(s). There's practically nothing you can't fix on these! Keep us updated, and send lots of pictures (we're nosy! :laugh:). Best of luck, cheers, and again, welcome! :cheers:
    Jim likes this.
  17. XSLeo

    XSLeo XS650 Guru Top Contributor

    An 8o being first registered in 79 isn't hard to under stand. Like most manufacturers, they start making a model year months before the year starts. On one list that has the year and model codes it, it tells the manufacturing year. This year starts August 1 and ends July 31. So anything built after Aug 1 of 79 are 80's. This lets them get the bikes in the show rooms in September or October. If an 80 gets bought as soon as it gets in the show room it will be first registered in 79.
    Do you have a multi-meter and know how to use it? if so follow the steps in the Charging system guide. It's not hard to check the system.
    Getting full battery voltage at the brown wire at the reg/rec and at the brown wire to the brushes is very important. Using a wiring diagram it's not hard to trace the power flow along the path from battery positive to the reg/rec and the brushes.
    Once you establish this power flow is at or very near to battery voltage on the brown wires is acceptable, as in with in about .2 volts of the battery and still get no charge when doing the jumper from green brush to ground, then you can check the ohms of the rotor and stator.
    I don't recall if the guide mentions it or not but when doing the stator ohm checks unplug the yellow wire to the safety relay. If not you will get a high reading when checking the white wire ohms, Some where around 20 ohms instead of .9 ohms The actual reading may not be .9, it may be a bit off. As long as all three white wires read the same is more important.
    Just a thought, do you understand how the charging system is supposed to function? It helps to know this so you can better determine what's not functioning right. A run down on the function is battery power is supplied on a brown wire to the reg/rec and one brush. When turn the bike on the regulator part of the reg/rec reads the battery voltage on the brown wire. If it reads low which it will untill you start the engine, the reg turns on a transistor, this grounds the green wire. This sends power through the rotor and this creates a magnetic field in the rotor.
    This magnetic field excites the stator to produce an AC current flow to the rectifier part of the reg/rec on the three white wires. The rectifier converts the AC current to DC current to charge the battery.
    When the voltage at the brown wire reaches the regulators preset level of about 14.5 volts it turns the transistor off, stopping the power flow through the rotor stopping the charging till the voltage drops below the 14.5 volts.
    This on/off cycle repeats itself very quickly. This maintains the battery at full charge.
    If the brown wire doesn't have the proper voltage, as in it's low, the reg/rec will think the battery is low even when fully charged. This is not good for the battery.
    Read the guide and follow the steps. You may find it's a low voltage issue on the brown wire or bad brushes. Only testing will determine the problems.
  18. Thanks for the info. Have ran a boat load of tests already.
    Rotor is 0 ohms.
    across brushes = 8.8volts , new brushes
    good battery
    No change in voltage across battery when rev engine to 3k
    Ground rectifier has no affect.
    Bike is in a garage. Have found a good stator and rotor, replacing them see what happens.
    Will update when know more.
    Jim and gggGary like this.
  19. 5twins

    5twins XS650 Guru Top Contributor

    If the rotor is reading zero ohms, that's probably the issue. Rotor failures are pretty common on these, unfortunately. When you get the new parts, I'd start by just installing the new rotor. That may be all you need.
    gggGary likes this.
  20. Bushyeyed1

    Bushyeyed1 Cafe Racer

    If it is your rotor @Jim is in the business of rewinding and does a mighty fine job. I got one of his rewound rotors and feel it was a better job than oem.
    Last edited: Feb 15, 2020
    Jim, gggGary and azman857 like this.

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