Question about 1985 Suzuki GSX-R 750 F

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Charging just before xmas i was out on the gixxer when it spluttered and started to fade, i noticed all the lights dimming as this was happening. nursed it home, put it on charge, consulted the workshop manual, broke out the trusty multimeter and tested the charging system as per the manual, there was zero output from the alternator. bought a second hand replacement from ebay, changed it, still zero output, have since bought another replacement, still zero out put, have i been unlucky enough to buy 2 dud alternators or could there be another issue?

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  • jason
    jason Jan 06, 2009

    have replaced the circuit breaker, replaced some suspect connectors, still no luck, as i said before the bike was running fine then all of a sudden started to fade, as if a switch had been flicked, it kind of felt like it had dropped a plug, so just to rule them out i replaced them, and just to eliminate them also changed all the fuses, i have checked all connections and terminals for continuity but still no good....

    any more ideas would be greatly appreciated as i am running out

  • jason
    jason Jan 08, 2009

    so yes it is a resetable circuit breaker,
    same voltage at the fuse box as the battery,
    brushes are good, not sure what the regulator IC is tho,
    all earth connections are good,
    what should ohmeter be reading on the fuses?

    i'll tell you what i have noticed tho, the output from the alternator is 70ACV, which i have been informed is correct, the wire goes to the starter relay, where it is crimped into the main red wire that goes to the battery, from this point it only shows 24ACV, could it be the relay? and if so could i not take the wire straight to the battery from the alternator?



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Hi jagga
I hate that when you don't know if a parts good or bad! I suspect that there may well be a problem elsewhere in the bike. Here is a link to get to a Haynes workshop manual for the machine. There are troubleshooting guides within that will assist you to sort it out. I suspect rectifier/regulator is the issue. The manual should be able to guide you to it. If you determine that the alternators are ok, bump em back to ebay again. Good luck with sorting it. electrical problems can be trying. If you need a friend to talk to about it, I am happy to help you out. I too am downloading the manual. Thanks for using FixYa
regards robotek

Posted on Jan 06, 2009

  • 2 more comments 
  • Graeme Ross
    Graeme Ross Jan 06, 2009

    Oh... like an idiot, I just read that you have a manual... still downloading mine, will comment back to ya when I have it :)

  • Graeme Ross
    Graeme Ross Jan 06, 2009

    OK, I have the manual now, Just wonderingwhat checks you have made on the alternator. I understand that you have checked to see if the charging circuit is working, but have you made any checks on the alternator/rectifier itself. On page 196 of the manual I linked you too, there is detailed instruction on how to  determine if the operating condition of the alternator, brushes, also tests to check the operation of the regulator. There is not much external to the alternator except for a fuse and basic wiring ascociated with the charge circuit  that may prevent charging from occurring. It is really bad luck to have purchased 2 faulty alternators, unless perhaps you have become unsuspecting game of some bikie cleaning out his workshop of layabout suspect parts. 

    I am really trying to assist you with your problem.  I am pretty savvy with electrical things(being a tech and all), Although I appreciate your rating, the  "the thanks for trying" rating is generally reserved for useless solutions, and has a negative impact on my ratings here.  I have gone to some lengths to help you, and prepared to go more...any chance of an upgrade?


  • Graeme Ross
    Graeme Ross Jan 06, 2009

    Have you checked the resetable circuit breaker to the charge circuit. Page 183 of same maual??

    Circuit breaker

    7 A circuit breaker (where fitted) is mounted
    behind the right frame cover or under the seat
    (see illustrations). If an overload occurs in
    the main circuit, the red button on the circuit
    breaker will pop out approximately 1 to 2 mm
    (0.040 to 0.080 inch).

    8 If the button pops out, let the circuit breaker
    cool for about ten minutes, then push the
    button back in.

    9 If the circuit breaker continues to pop out,
    check the wiring harnesses for a short. Never,
    under any circumstances, bypass the circuit
    breaker or replace it with a breaker of higher
    capacity - the overload could damage

  • Graeme Ross
    Graeme Ross Jan 07, 2009

    Hey Jagga

    Ok, lets go through a Q and A and check things from the ground up. If you could answer a few questions we can eliminate things as we go. 

    1. Is the circuit breaker you replaced a resettable type with the red button.

    2. With the bike running lights on, check the voltage on the 10 amp fuses at the fuse box. Are they the same as you can meter at the battery

    3. Have you checked the brushes in the alternator, and also that there is a regulator IC fitted to the ones you purchased off ebay

    4. check all the major earth lugs to chassis for corrosion

    5. are all the 10 amp fuses metering ok with an ohms meter.
     The circuit for the charging circuit is relatively straight forward. If you can check the above and get back to me with what you find.There are other things we can do, just need to know these things first. 

    How bout the upgrade to FixYa rating for my efforts :) Cheers




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