Old projector motor bypass hack

Discussion in 'The Projects Forum' started by Amiga4000, Mar 22, 2017.

  1. Amiga4000

    Thread Starter New Member

    Mar 22, 2017
    Hi, this is my first post :) I do not have a great deal of knowledge with electronic circuits other than the basics so please be patient if my terminology is not quite right :)

    Ok now to my project, basically I've got a few old projectors (Hitachi ED-A101s) two of which are suffering a common fault which is a mechanical failure within the mirror motor gearbox assy. the failure is very common and as such I'm looking to bypass the mirror motor so that the mirror can simply be opened by hand. The perfect hack would be to modify the firmware but reverse engineering lines assembly code would be a nightmarish task.

    Now the problem and project requirements..

    The problem is that the projector monitors the mirror using a changeover switch triggered by a cam this switch (via some resistors) returns a signal to the SoC telling it what position the mirror is in. The movement is also appears to be timed in the firmware so if it's too fast or too slow reaching a position it fails and shuts down. As such we can't simply unplug the motor :-/

    From the service manual schematics it appears that the cam / switch works as follows

    Endpoint 1 - return output ~1mv
    Travelling / Moving - return output 2.43v
    Endpoint 2 - return output 1.59v

    My idea is to take the motor input (+12vdc or -12vdc depending on direction) use it as a trigger input to a circuit that emulates the correct cam switch response allowing us to use our projectors without these dreaded gearbox failures, they are used primarily by our community group who are a non profit group so don't have the funds to replace the gearboxes every time they fail.

    The circuit would need to have a method of adjusting the time delay between endpoints (emulating motor travel time) e.g. :-

    Endpoint 1 (1mv) --> moving 8s (2.43v) --> endpoint 2 (1.59v)

    Endpoint 1 (1.59v) --> moving 8s (2.43v) --> endpoint 2 (1mv)

    Any ideas and or advice, would be greatfuly received.
  2. Amiga4000

    Thread Starter New Member

    Mar 22, 2017
    In order to give as much info as I can this is the circuit diagram for the cam and switch assembly that monitors the mirror motor position.

    The jumper connections are as follows :-

    3.3v = 3.3v supply from the main PCB.
    M-ST = Returns motor position either Endpoint A, Endpoint B, or Moving / Travelling
    GND = GND.
    ANGLE1 / ANGLE2 = Not needed in the project.

    Last edited: Mar 23, 2017
  3. Amiga4000

    Thread Starter New Member

    Mar 22, 2017
    Problem solved, simply used Arduino mini, which was quicker and simpler than building a custom circuit.
    Last edited: Mar 27, 2017
  4. A Homeschoolers Workbench


    Jul 26, 2016
    Good idea:).