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Thread: K75 Tach Problem

  1. #1
    TESLAESQUE
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    K75 Tach Problem

    Hi all,
    I'm having some trouble with the tachometer on my K75. That is to say, it doesnt work at all.

    I had an instrument cluster light that was improperly seated, and sometimes the cluster would be partially unlit...so i'd tap the crystal until it came on. I went a little overboard at one point and cracked the clear plastic over the tach. The next time i rode in the rain, it went haywire for a while, then died. I've purchased a used tach that was sold to me as working, and have swapped them but to no avail.

    I have carefully inspected all of the circuitboards inside my cluster, and see nothing "fried".

    (1) Am I correct in assuming that this problem "MUST" be the result of the broken tach?
    (2) Is there a way to troubleshoot this systematically through each component in the instrument cluster?
    (3) Has anyone had something like this happen before?

    Thanks in advance.

  2. #2
    A bozo on the bus deilenberger's Avatar
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    Quote Originally Posted by Teslaesque View Post
    (1) Am I correct in assuming that this problem "MUST" be the result of the broken tach?
    Must seems such an absolute. I'd say no. You don't know the tach IS broken - you know it doesn't work.
    (2) Is there a way to troubleshoot this systematically through each component in the instrument cluster?
    Practically - probably not. I've never heard of a troubleshooting guide to the components in the cluster.
    (3) Has anyone had something like this happen before?
    Yes. People have. Causes have varied.
    Thanks in advance.
    I'd suggest visiting http://www.ibmwr.org - and look for the K-tech pages. There are several writeups there on instrument cluster repair. They may have some helpful info for you.

    I suspect the problem may be in the pod - but perhaps not the tach assembly.

    The circuitry inside the K pods is a bit strange to begin with using flexible circuit boards and push connectors. It was probably really high-tech in the late 70's when it was designed. You want to make sure all the circuit interconnects are good..
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders
    '12 R1200R - I love this bike!

  3. #3
    TESLAESQUE
    Guest
    thanks for your help. I wish i could get my hands on some more technical information that isnt available on ibmwr...like what kind of a multimeter reading i'm supposed to get at the wire that drives the tach, etc.

  4. #4
    TESLAESQUE
    Guest

    Tachometer fix?

    Just thought I'd give an update...and to make a record for future searches on such a strange problem...

    There is a wire, visible on the wiring diagram in the riders manual, that goes from the #1 cylinder coil, straight up to the instrument cluster. It functions to send a pulse, every time the coil discharges, to the tachometer to let the rider get a reading.

    This wire is black and blue. It corresponds to the fourth pin from the top on the speedometer side of the instrument cluster housing.

    After removing the cluster, and circuitboard therein, there is a rubber mat that fits over the pins inside. I removed the mat to find the corrosion that kept it from sending power to the tach.

    I've tried to attach a photo to illustrate the problem. The power impulse from the coil to the tach comes in from that 4th pin from the top on the right side. Then, the 4th pin connects through the ribbon cables up to the connector in the top left corner of the image (those three brass circles in a horizontal line). Specifically, it goes to the one on the right.

    I'm off to attempt a repair with a soldering iron...which is uncharted territory for me.
    Attached Images Attached Images

  5. #5
    Registered User
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    Why don't you just find an electronics tech and pay them to do a proper soldering job on it.
    '03 R1150R, '03 F650GS, '97DR200SE,'78 Honda CT-90, '77Honda CT-90

  6. #6
    TESLAESQUE
    Guest
    I did my own proper soldering job on it...fixed it myself and learned something in the process. Thanks for your help.

  7. #7
    BMW uber alles! Zagando's Avatar
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    Good on ya, Teslaesque; I was just about to advise that you clean the circuit board and whatever you were going to solder very well with rubbing alcohol before you solder---looks like it all worked out for you already.

    Thanks for posting the photo and info; I'm sure it will come in handy to others here at some point. Corrosion and the breakdown of the pod gasket seems often to be the culprit in many early K-bike maladies, doesn't it?
    ---Jeff

    ex: K75S Berlina R100GS/PD , K100RS , R75/5 , R60/2

  8. #8
    mrich12000
    Guest
    Post this to the ON great story..

  9. #9

    checked all the above, then....

    I dismantled all the above and found no corrosion on any of the connectors so.... cleaned all the connectors at the coils and bracketry, checked for continuity from the Black/blue coil wire to the 3 brass circles in the pic above, reassembled all and now have a functioning tach on 3 different rides over 2 days. I'll call this a success story.

    I tried to pull the tach needle off to look further into the tach but couldn't so thought to leave "sleeping dogs lie."

    Next problem to remove a seized grub screw in the ignition switch. Simple job until the screw wouldn't turn, now it's a drill out job.

    After 5 years of outside winter west coast storage I'm glad it's a beemer.
    thanks
    bricker2

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