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Thread: mileage indicator does not work

  1. #1
    Randy Guest

    Post

    I have a 91 Buick Regal. The speedometer is digital and it works and my cruise control works. For some reason my mileage indicator does not.

    __Does the mileage indicator run on a cable or is it electric?
    __Any ideas as what I should check?

  2. #2
    Mopar Guy With A Buick Guest

    Post

    The odometer on the Buick is driven from an AC frequency that is fed to the computer. The freq. is generated by a sensor on the tranny. The computer then sends a negative going square wave to an 8 pin DIP located next to the odometer. The chip then sends a stepper motor drive signal to a small motor which in turn drives the numerical display. The problem is the 8 pin chip is prone to failure because it is underrated. The chip is a Cherry Semiconductor CS8442. It is next to impossible to buy in lots less than 100. To overcome this problem I bought a NTE 1857 16 pin dip H stepper motor driver for $12.00. The chip will sink a load at 350 ma versus the Cherry unit at 85 ma. By removing the digital display and referencing a schematic a negative going pulse can be added along with ignition voltage to make the unit work on the bench. Tie pin #10 of the NTE chip positive for ccw generation. Tie pin #9 low for full step motor sweep. Heatsink the center pins (4), insulate the new circuit board and use prints (can be found on-line) for both the old chip and new chip to run four wires from the new chip to the old board to drive the motor. This is nothing more than a simple H configuration stepper motor driver circuit. Cherry Semi apparently wants to keep all automotive electronics out of the hands of the common guy. This work around solves that problem.

  3. #3
    Join Date
    Sep 2004
    Posts
    383
    Rep Power
    20

    Post

    a (really)low tech alternative would be to buy a junkyard piece

  4. #4
    Mopar Guy With A Buick Guest

    Thumbs down

    This was my thinking on the first two attempts. Trouble is the junkyard pieces are just that. I couldn't understand why the junkyard cars had such low milage. Turns out the chip failed in the same manner. Getting a new display doesn't help because you still have the lame chip. What the engineers didn't figure on was the temperature extremes the enclosed chip would be subjected to as well as the inevitable dust which makes the odometer turn harder after it gets dirty.

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