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Thread: '73 R75/6 Generator Problem?

  1. #1
    Registered User pandry1's Avatar
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    '73 R75/6 Generator Problem?

    I haven't been able to ride much this summer due to constant daily rain here in the mountains of NC. However, the sun came out today! I charged my battery and jumped on for much belated spin around the neighborhood.

    Problem - when I turn on the ignition, the generator light comes on as it should. After starting the engine, the light goes out - as it should. However, as I increase engine RPM, the light come on dimly, then gets brighter as RPM increases. Can someone help me diagnose this problem? Diode Board, Rotor, Battery? What do I check first? Please e-mail me at pandry1@frontier.com if you have suggestions. Thanks!

  2. #2
    Administrator 20774's Avatar
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    Changed the battery and now the light comes on!! Interesting coincidence! Be sure and check all your battery connections.

    I'd first put a voltmeter across the battery terminals just to confirm what you're seeing throught the light. More than likely, you're not seeing any voltage increase at the battery.

    There are specific steps to isolate the problem. One source will be Snowbum's website...he has a section on troubleshooting the alternator. The second is Rick at Motorrad Elektrik. He has a booklet that walks you through the various tests. The third is to look at the Resources and Links section of the forum under the Charging and Electrics section...there are other resources there.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  3. #3
    Registered User m_stock10506's Avatar
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    Note, that the OP says he CHARGED the battery - he didn't change it. It could be as simple as loose wiring connections or some corrosion at the connections. I would check the battery terminals for both issues, then follow the wiring and check for tight clean connections. If that doesn't clear it up, then go to the web sites just mentioned and follow the diagnostics there.
    Michael Stock, Trinity, NC
    R1100RT, R100, R60/6

  4. #4
    Administrator 20774's Avatar
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    Yup, missed "charged". Still, it sounds like the battery is the first place to look. It might not be holding a charge or it might be weak. Watching the voltmeter across the battery terminals while starting might tell a lot.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  5. #5
    James.A
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    I experienced that very same symptom once on one of my R75/5's. I can't remember if it turned out to be the alternator rotor or the diode board. What happens is that the light gets brighter as the battery gets deader.

  6. #6
    James.A
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    Quote Originally Posted by 20774 View Post
    Watching the voltmeter across the battery terminals while starting might tell a lot.
    This is a GREAT idea! It will also reveal a failed charging system. You can observe the system from resting voltage, to voltage drop when the starter engages to, charging voltage where the system is replacing electrons just used to roll the starter. If you use an analog meter, it will show the needle sweeping up to the output limit of the voltage regulator which would be around 13.5 volts. If you do this and the needle/indicated value returns to "resting voltage', you'll need to investigate further.

  7. #7
    Registered User donmitt's Avatar
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    My R80RT had a similar problem as the rpms increased, the light came on brighter. My problem turned out to be the springs for the brushes were not holding the brushes down tight enough to the rotor. when I wrapped the spring one more time around the anchor the problem was fixed. This of course may not be your problem but it is something else to check.
    Don
    Don Mitchell

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