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Old 11-28-2003, 08:06 PM
Q Q is offline
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Join Date: Aug 2000
Posts: 839
W126 Cruise Control Repair

I've managed to repair my third circuit board by resoldering. So far, I have resoldered my Idle Speed Control, Fuel Pump Relay, and now my Cruise Control Module. This one was by far the hardest. Not because it was so hard to solder, but because there was an anti-corrosion coating that got in the way.

My symptoms were surging or non-functioning cruise control. Sometimes, it would work fine and then it would flake out again. I could put my foot on the gas pedal lightly and feel it moving in extremem opposite directions (not well regulated).

To repair, I pulled the bottom dash panel by removing the two covers on either side of the steering wheel down where the change well is. I also had to remove a screw and a friction fastener (one was missing) from the underside. The panel then slides forward and out quite easily.

From underneath, you can see two metal boxes with electrical connectors that sit side by side. The larger one is the cruise module. It is unnecessary to remove the boxes, as you can simply uncrimp the soft metal tabs that hold the circuit board in. The board slide easily out.

On the circuit board, you will find a piece of foam glued on. I peeled mine off and then dripped Goo Gone on the remaining tape strip to soften it up. It picked off easily after that.

The most important thing to do when reworking this board is to burn off the corrosion coating before you start soldering. It took me a while to figure out that this was the best way to get the solder to stick. I highly recommend getting some soldering flux for this job, as the corrosion coating played hell with my efforts. The brush on flux would have saved me a lot of grief.

Heat each joint briefly so that the solder melts and you see the corrosion coating liquify. You will notice that the solder almost pulls right off of the pad on the circuit board for some of the joints. The board design was pretty bad, as those holes are FAR too large for a lot of the pins and require too much solder to make the connection.

Once you have heated each joint, brush some flux on a small area and use a fine tip iron and some fresh solder to rewet each pin and pad. It will take a while to do the whole board, so find a comfortable place to work. Be careful of that hot iron and your surroundings.

If you do not own any soldering equipment, you can pick up everything you need at Radio Shack for under $20, I am sure. Contrast that with the $230 part replacement and you can see that it is worth the effort to give the soldering method a shot.

Good luck and message me if you need some help.
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