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Thread: Autohelm 800 power transistors

  1. #1
    Join Date
    Jan 2015
    Posts
    1

    Default Autohelm 800 power transistors

    Hi,
    Our trusted Autohelm 800 started a mutiny, and after opening her up the problem appeard to be fried power transistors.

    Two of the four transistors on the position TR4 and TR8 were fried beond recognition
    the others were;
    BDW 93B 8923 on position TR7
    and
    BDW 94B 8917 on position TR 6(?)

    My question to the gathered wisdom here is; what were the typenumbers of the unrecognisable transistors?
    Bonuspoints question ;-) whith which type of transistors could all four of them best be replaced?
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  2. #2
    Join Date
    Aug 2009
    Posts
    20

    Default

    A little googling shows that the 93B is a NPN while the 94B is a PNP darlington transistor. An H-Bridge circuit would make sense for the motor driver and this circuit takes 2 NPN and 2 PNP very commonly. Using the pinout from the data sheets you could probably trace the power, ground and motor wires to see which goes where: PNP would be connected to the +12V and the NPN would be connected to the (-)


    Some references:
    http://www.nathandumont.com/blog/h-bridge-tutorial
    https://www.fairchildsemi.com/datasheets/BD/BDW93C.pdf
    https://www.fairchildsemi.com/datasheets/BD/BDW94C.pdf

    Tell us how it goes!
    -Mike
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    Last edited by breezetrees; 01-16-2015 at 04:16 PM.

  3. #3
    Join Date
    Jan 2008
    Location
    Santa Rosa
    Posts
    545

    Default

    An underlying question is "why" the transistors failed. A power spike? Before just replacing the transistors, I'd look further back in the system. -- Pat

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