guys..i need help with this lcd display used on ebikes pls.

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  • vikivng
    Badcaps Veteran
    • Feb 2019
    • 228
    • uk
    #1

    guys..i need help with this lcd display used on ebikes pls.

    This is an lcd display used on ebikes.
    long story short, there was condensation inside the unit.
    I opened it and thoroughly cleaned the pcb with isopryl.
    The board had no visible corosion.
    It powered on fine and was tested for an hour or so.
    However when connected to the bike,,it did not power on at all.
    I took it home and reopened it to take a look. There are no shorts based on MY testing.
    However,,when I probe the transistor and the mosfet gate in diode mode or contuinity mode, (one probe on transistor collector and one probe on mosfet gate}the unit powers up.
    Aslo with one probe still on collector and the other probe on any of the 2 resistors close to the mosfet ,,the unti powers up.
    If an NPN transistor in installed instead of the PNP, THE UNIT COMES ON AS SOON AS POWER IS APPLIED. However , it can be turned off with the power button in this state but will not turn back on with the power button.I dont know what to do next to fix this..pls help
    The large mosfet and the transistor are picture at the edge of the board.
    I believe htis circuit is the emitter follower circuit.
    I am getting full battery voltage at the gate of the mosfet, 40v at the emitter and 39v at the base.
    I dont understand why the transistor never turns on the mosfet.
    Attached Files
    Last edited by vikivng; 09-16-2025, 01:42 PM.
    Tags: None
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