Many owners of early-model (74-78) 240s live with broken dash clocks. What you may not know is that repairing the clock is often both easy and cheap, provided you have some basic skill with a soldering iron.
In this article, we are going to replace the two 100µF/16V (that's 100 micro-Farad, 16 volt) electrolytic capacitors found in the clock. You will need to start by acquiring the following items:
Parts and tools list
- 2 x 100µF polarised electrolytic capacitors ($0.36 each in Australia)
- 1 x soldering iron
- 1 x spool of solder (the original solder is tin/lead solder, so ideally you want to also use tin/lead solder)
- 1 x solder removal tool (sometimes known as a "solder sucker")
- Some small imperial ratchets (about 7/32) or a pair of pliers
- 1 x flat head screwdriver
You will first have to remove the clock from the car. To do this, remove the rubber trim below the panel that houses the clock and two centre air conditioning ducts. This panel simply slides downwards with a small amount of force.
This will reveal two screws. Remove these, and the centre panel should lift out.
Here's the panel, with the clock indicated by a very patronising arrow:
Next, we need to remove the clock from the dash section. To do this, remove the two nuts indicated in the next image:
Once that's accomplished, simply slide the clock assembly forwards and out of the dash.
Before removing the rear panel of the clock, we will need to desolder the pin marked by an exclamation mark in the image below. This pin connects to the Printed Circuit Board (PCB) behind the clockface, and provides the ground connection for the circuit.
Use your soldering iron and solder sucker to remove the solder holding it in place.
Next, remove all the bolts and screws indicated by the other arrows in the image.
At this point, I recommend wearing a pair of very clean latex or nitrile gloves. This will prevent you accidentally putting fingerprints on the clockface. In general, try your best to avoid touching the clockface at all. Hold the clock by the edges of the face, or do as I did and leave it sitting inside the front housing.
Now we need to remove the protective foam that covers the circuit board. There is also a brown plastic piece that shrouds the earth pin. Now, on my clock, the solder on that pin had broken, and it came out with the backplate. If this happened to you, just desolder the metal pin from the housing and put it aside for the time being.
Okay, we have now arrived at the guts of the clock. If you look from the side you will see two brown cylinders on one side of the clock. These are the capacitors. If you see any white spots around the tops of the caps, they are almost definitely blown. Even if yours look fine, you're this far, and two replacement caps will set you back about 70 cents. Peanuts!
In the image below, I have indicated the capacitor pins, along with their polarity ( + / - ). The other pin refers to the ground pin. If yours hasn't broken off, just ignore this. If you look closely you will see the negative terminal of the capacitors is also printed on the PCB itself, so when in doubt, check the PCB!
Using your soldering iron and solder removal tool, remove the two capacitors from the board.
Here are our culprits:
Now that they're out, we can take our new capacitors, which should look like this:
and put them into the circuit. Once you've positioned them and soldered the pins, clip off the excess wire.
IMPORTANT: remember, the capacitors are polarised. This means if you put them in backwards you might blow the circuit up. Capacitors normally have a stripe on them indicating the negative pin. It looks like this:
At this point, if your ground pin is broken, resolder it onto the board, in the position indicated in the images above (the arrow with the "earth" symbol on it). You may need to clean up the pin to get the solder to bond properly. You can do that with some 1200grit wet and dry sandpaper, or a knife, or just about anything abrasive. You're just trying to remove the dirt and oxidisation from the surface of the pin.
When attaching it to the PCB, make sure you get it positioned perpendicular to the board surface. This way it will line up easily with the hole in the clock's rear housing.
Now you are ready to re-assemble the clock. In true Haynes style, assembly is the reverse of disassembly. First replace the foam padding, then the plastic ring around the ground pin, then slide it carefully into the rear housing of the clock, making sure the ground pin slots through its hole. Replace the three flat-head screws holding the rear housing on, and then the four bolts that hold the front housing on, making sure you get them in the right spot (so that you can secure the clock assembly to the dash panel with the two remaining nuts).
Now that everything is securely in place, solder the earth pin to the clock rear housing.
If you're feeling confident, just re-install the clock in the car and listen for a ticking sound. Otherwise, a 12V battery trickle charger or simply wiring the clock directly to the car battery will allow you to test that it is functioning correctly.
If your clock still doesn't work, I first recommend re-checking your work. If you find no problems, it might be that your clock's motor has seized, or the IC or quartz crystal has failed. I did not disassemble my clock far enough to discover what IC controls the clock's movement, so you will have to venture out on your own.
Still, aside from the gears and motor, every electrical component in these clocks should be fairly trivial to replace.
