How to test your CT90 Rectifier

Discussion in 'CT90, CT110, ST70, ST90 Discussion' started by MikeCT90, Jun 28, 2018.

  1. MikeCT90

    MikeCT90 New Member

    Joined:
    May 10, 2017
    Messages:
    20
    Likes Received:
    8
    Malm likes this.
  2.  
  3. b52bombardier1

    b52bombardier1 Well-Known Member

    Joined:
    Dec 26, 2010
    Messages:
    1,890
    Likes Received:
    137
    Great write up. Very good explanations and pictures. However, I tend towards a simpler method. With the bike running at around half throttle, I test for the presence of AC voltage at the battery posts. Much more than about .1 to .2 volts AC (a tiny amount) means that one or more of the diodes in the bridge rectifier is leaky and passing AC to the battery - not good for the battery. Time to change the rectifier to the flat square type with the four post blades in your post. The trouble with my method here is that cheap, autoranging multimeters often display confusing results with small amounts of AC.

    For pennies extra cost, I usually go with the 1000 volt peak inverse voltage rectifiers. There is absolutely nothing coming out of a 90 CC Honda stator that can harm a 1000 PIV rectifier. It'll just laugh.

    Your test is certainly more thorough than mine but I'm the lazy type . . .

    Rick
     
  4. Malm

    Malm New Member

    Joined:
    May 28, 2011
    Messages:
    7
    Likes Received:
    0
    Thank you for the write up, I need to test rectifier, condenser and coil on my newly acquired ST90, as I have no clue why I am getting no spark... this will help me a LOT.
     
  5. Malm

    Malm New Member

    Joined:
    May 28, 2011
    Messages:
    7
    Likes Received:
    0
    My rectifier checked out ok.... but you state: For this coil the reading is 9.43K ohms which is good and is under the 10K ohm limit typically used. My coil checked 22.8K ohms....
     
  6. b52bombardier1

    b52bombardier1 Well-Known Member

    Joined:
    Dec 26, 2010
    Messages:
    1,890
    Likes Received:
    137
    Coils, by themselves, rarely fail on these bikes. I'd hazard a guess that the resistance has gone high in the high tension spark plug lead and / or the plug cap - all replaceable at www.dratv.com.

    Do you have a no kidding good six volt battery? With the key on, good battery and the run / start switch to run, do you have six volts available on the flat points spring?

    Rick
     

Share This Page