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Clock Repair Procedure

for Mercedes-Benz Automobiles

Introduction

The technical material for this FAQ (Frequently Asked Question) was provided by various Mercedes-Benz enthusiasts (primarily Jim Mahaffey), was edited by Richard Easley of Baylor University, and is provided as a service to the subscribers of the Mercedes-Benz Discussion List.

To receive similar quality tips as described below on a daily basis, consider subscribing to the Mercedes-Benz Discussion List, which is located at the following site:

http://hsb.baylor.edu/html/easley/mercedes/welcome.html


Assumptions

Using the categories of mechanical ability from the Mercedes-Benz Discussion List <http://hsb.baylor.edu/html/easley/mercedes/subscribe.html>, you need to be at the level of "Medium Do-It-Yourselfer" at minimum, to repair your Mercedes-Benz clock. If you are below that level, you may want to provide these instructions for someone who is at the medium level or beyond.

 

Introduction

Most later model Mercedes-Benz clock failures are due to a bad capacitor (or capacitors) on the back of the clock. Removal of the instrument cluster to gain access to the clock is a simple process with the use of two special tools that can be made from common household items. You do not have to be an electrical engineer to do this procedure. The electronics on the clock consist of only 4 or 5 components, so identification is easy.

Tools needed for repairing late model Mercedes-Benz clocks
  1. High powered flashlight or shoplight.
  2. A small low-wattage soldering iron.
  3. De-soldering tool (not mandatory, but nice).
  4. Rosin-core solder.
  5. A miniature screwdriver set (flat blade).
  6. Meguiar's Plastic Cleaner.
  7. Meguiar's Plastic Conditioner.
  8. Dash removal tool (Special tool: handmade). To make, fashion a non-OEM factory instrument panel tool out of a a thin coat hangar by doing the following: a. cut the long bottom strip to use as the tool. b. put a 75 degree bend at one end with a couple of inches of extra wire. c. cut the bent wire about 1/4 inch from the bend with a pair of wire cutter and leave a "sharp" edge with the cut. At the other end of the coat hanger, fashion a circular handle out of the excess, leaving the whole tool around 4-6" in length.

    Parts needed for repairing late model Mercedes-Benz clocks

    1. Radio Shack part number 272-1028. You will need two of these capacitors, and they only cost around $1.00 each. These are the only parts needed.

    Instructions
    1. If your car has a telescoping steering wheel, fully extend the wheel (as far away from the dash as possible). (If it doesn't have this feature, you can still probably do this without removing the steering wheel by judicious wiggling.)
    2. Using your instrument panel (IP) removing tool (which you built with pride), slide the tool in between the IP and the left side of the dashboard at the 10 o'clock position, with the hook facing down and parallel to the side of the instrument cluster. Push the tool all of the way in. Turn it 90 degrees to the right so that it engages the instrument panel. Grabbing the tool's handle, pull the left side of the IP out carefully, until the tool's hook just clears the dashboard.
    3. Repeat step 2 on the right side at the 2 o'clock position.
    4. Put a large clean towel on your workbench.
    5. You should now be able to grab the IP by hand. Pull it out at the right.
    6. Start unplugging things. If the oil pressure gauge has a "live" oil line, unscrew it and cover the open line with a piece of rubber-banded plastic. You'll want to mark the bulb assemblies with numbers if they are not already marked (mine were -- I'm not sure if from factory or not.). Unplug everything.
    7. Remove the IP from the car to your bench.
    8. Lay the IP face down and carefully note ordering of instrument "pods." Mine had three.
    9. Remove the pods carefully and place in a non-scratchable location.
    10. Using the Meguiar's products, clean and condition both the inside and outside "glass." It'll take a while, but you'll be pleased with the result. Somehow, the inside glass accumulates dirt over time.
    11. Plug in the soldering iron to let it warm up.
    12. Now, to the clock. The clock's hands remove easily with your fingers (notation of positioning is unimportant at this point), but the tachometer's needle is better left alone.
    13. Remove the three flat screws on the front of the combo which hold the tachometer to the instrument facing.
    14. Put the combo face down on the towel.
    15. Remove the rear screws which hold the tach and the clock.
    16. After removal, you should now be able to separate the combo enough to remove the clock as a component to work on.
    17. Don't forget to "save" the rubber gasket on the back of the clock for installation at the proper time.
    18. Place the clock face down on the towel. Find the capacitor(s). They are about 1/2 inch long and round. (the only other electrical components are: 1 resistor, a crystal, and an integrated circuit).
    19. Note the direction of the capacitors (there should be a "+" on one end.)
    20. Using the soldering iron, and a large miniature screwdriver for leverage, "de-solder" the capacitor (or capacitors), placing the screwdriver blade between the capacitor and the circuit board for leverage. You'll have to do this in stair-step fashion, since the solder will probably harden before you can remove the whole thing at once. After removal of the capacitors, "clean" the wire holes by heating the solder and shaking it off. (Note: a "desoldering" tool will work more effectively during this step, but it is not mandatory.)
    21. Install the new capacitor(s), without cutting their "leads." Note that the Radio Shack replacements have a "-" instead of a positive marking direction.
    22. Cut the leads at the edge of the solder joint.
    23. Reassemble and reinstall everything.
    24. When putting the clock the clock hands back on, align them both at 12 o'clock.
    25. Turn the hands for a few revolutions using the setting knob and align as necessary.
    26. Finally, let me know if you complete this procedure successfully; it took a while to type this, and I'd appreciate knowing when each person has completed the repair! Please e-mail me at richard_easley@baylor.edu

To receive similar quality tips as described above on a daily basis, consider subscribing to the Mercedes-Benz Discussion List, which is located at the following site:

http://hsb.baylor.edu/html/easley/mercedes/welcome.html

 

©1998
Richard Easley, Waco, Texas and Stu Ritter, Denver, Colorado.

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