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Modern replacement for seat motor controls.

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  • Errcl65errcl65
    Participant
    Post count: 15
    #14105 |

    This is going to be on going issues with most of the 780s.   The full motor drive current

    is being run across the 4 switches.   Over time and use, the contacts are going to arc and

    build resistance and increase the current drawn to drive the motors.   All of these will

    lead to motor burn out or control burn out.    I am going to design and build bridging

    board with sealed relays to actually deliver the power to the 4 motors and use the existing

    control head just for control.   Likely use a bank of 1-wire relays,  an Arduino (Nano) to

    process the commands from the control head to switch the relays.   It should all fit in

    under the control head.

    LagerLager
    Participant
    Post count: 91

    Sounds wonderful! Please send the results here once everything is ready!

    Johan VlagsmaJohan Vlagsma
    Participant
    Post count: 71

    Actually on mine there are already relay’s under the seat. The switches control the relais through the black box under the seat. I’ve had a black box fail but not the switches. Mine is a 1990 model 2.

    Errcl65errcl65
    Participant
    Post count: 15

     

     

    I have totally disassemble the power seat controls and black box on the 89.

    The black box under the seat augments the forward/backward travel for the
    fold down feature. It does not process the other 3 controls, only
    forward/backward.

    This board is really scary old complicated TTL analog tech. It intercepts
    the forward/backward control from the stock head units and adds forward control
    when the switch releasing the fold forward is depressed and held. There is
    also a limit switch at the back of the seat (ball bearing which contacts the
    side console) to stop the forward motion (forward position reached).

    This board can be completely by-passed with the loss of the fold forward
    feature, returning the seat to a stock 760/960 style. One just has to manually
    more the seat forward.

    I think my black box is shorting out the seat motor 30A fuse. I manually
    test all the 4 motors (using a battery to power each motor in both directions)
    and they are good.   I had the control head out already, and took the opportunity to rebuild it.

    I separated the control head (remove all the button, arms, ball bearings), and
    desolder the board to reveal the 2 relays and 4 diodes. I remember doing this 25+ years
    ago with my 740 Turbo to fix one of the bad relays. Just go slow with low wattage
    iron (solder sucker and wick), slowly pry the board up and away from the housing as
    you desolder. Start from one end and work (pry up) towards the opposite end.
    The board is essentially fasten to the housing via the solder joints (23 of them).

    The relays in the control head are $5.00 parts from Digikey. New version are
    pin compatible and seal! Digikey part is 1393277-4 (Open K Relay, 12VDC, 45AMP).
    The diodes 1N4007 don’t break typically, but they are pennies.

    If the fold forward feature is really important, it can be mimic-ed using
    an Arduino PLC and some relays.   This is low on my restore priority.

     

    DaviesDavies
    Participant
    Post count: 124

    Thank you for this excellent write up. Please continue to show these helpful repairs. I know there are other 780 folks out there with similar issues.

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