My cruise control works intermittently. What I mean is that sometimes when I turn the car on, the cruise works, and works well, until I shut it off. Then the next time I start it up it may or may not work.

Seems like it is something simple, where should I start?

Thanx

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1987 300E

Most of the time (99%), if the switch is good, the cruise amp is faulty. The amp is the control unit. It is located under the driver's kick panel. It is a silver box. They do offer rebuilt units, but you will need a coding plug for the newer control unit.

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Benzmac:
Donnie Drummonds
1991 GMC Syclone
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

I have the same problem. What is a "coding plug"?
P E H

There is now a universal cruise control amp but, you need a special coding plug to configure it for your specific car.
Another option is to get a rebuilt amp that is an exact replacement for your old amp.
We have both in PartsShop.

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Bill Wood - Webmaster
MercedesShop.com, LLC

I used to have that problem with my Cruise Control as well – now it works perfectly, without a hitch! The solution was to resolder the CCA board. Many others have done this procedure with the same results.

The CCA seems to be another of those problem areas that everyone inevitably has to deal with after 10 or 15 years. Fortunately, like so many of the systems on this car, you can fix it yourself at minimal cost. In this case, 50 cents worth of solder and a couple of hours of your time.

When you pull the CCA and examine the board you’ll probably find that it looks ‘like new’, with no signs of burned components or broken traces. Nevertheless, what has likely happened is that one or more solder joints have loosened up due to deteriorative aging. The defect will Not be visible. You should systematically resolder each connection on the trace side of the board using the appropriate tools, solder and practices for electronic circuit boards. Then (using a magnifying glass) carefully inspect the board for solder bridges and remove them with desoldering braid.

I’ve done boards where I’ve also replaced the ICs, but this is usually to correct a total failure. Your symptoms suggest a deteriorated, intermittent solder joint. You could also replace your ICs (either 1 or 2) for about $1 while you’re at it.

After reinstalling the board in its case, you should also clean the external pins and apply a contact conditioner (available from computer and electronics shops).

Good luck, let me know if you have any questions.
Barrie

Is there a special tool to open control module to gain acess to the circuit board or will a screw driver and pliers do job? I have my module out of the car but I did not want to potentially damage module trying to get to board.

Spine Doc did you try Barrie's suggestion or buy a rebuilt? Johnny

Yes I actually did resolder the board. My Aunt works for Digital and makes motherboards and circuit boards for a living. After resoldering and checking all the diodes the cruise control works PERFECTLY! No intermittent, etc. Note that even with special magnifying glasses you will not see any breaks in the solder. My understanding from my Aunt is that there is not so much breaks in the solder, but the solder itself flexes and "unattaches" from the circuit board and the solder point itself. When you solder a bad solder you will see it "suck" the solder in, as my Aunt describes it.

I also resoldered my climate control unit fixing this, and saving me a couple hundred bucks.


Barrie---where do you buy the IC's? My Aunt said you could not test them since you would need a propietary diagnostic tool connected to the amp. And by the way there are a ton of IC's on these units. She also said the IC's were most likely programmed, so if you replaced you would just be replacing with blank IC's. Tell me if you know anything different.

Glad to hear the re-soldering fix was successful!

The last CCA in which I replaced the IC was for a model other than a 124. It contained only one IC (an LM2901, which is a readily available 'quad comparator' at 50 cents).
When I did the CCA on my 124 I only did a resolder job; since that fixed the problem I didn't even look at the ICs. If you let me know the part no. and number of pins for each IC, I'll try to source them for you.

Barrie

Johnny,
You don't need anything special. Screwdriver and pliers work fine to lift (and reset) the tabs. The case is soft aluminum.

Hey guys. Re-soldered CCA board and unit works fine now. Thanks for the assistance. Johnny

I am now going to replace my non-functioning Radio Shack soldering iron and do mine next weekend. Oh wait, going to meet with the Cobra club next weekend. I am really getting too addicted to cars. My wife is going to kill me. I am babbling again, aren't I?

[This message has been edited by Q (edited 08-26-2000).]

My Cruise control pulses. I expect it just needs to be rebuilt like the ones you guys describe. I know I should just do it, but I wanted to post the question. Will I need any new circuits, or will a rebuild do the trick.
Thanks

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Kyle De Priest
1986 300e
1972 BMW R75/5 (Best there is)

The general consensus is to heat the solder joints to get them melted. If there was a bad joint, it should be fixed. If that doesn't fix it, try replacing some of the readily available chips that are on the board. If your skills aren't up to it, you will have to get a rebuilt unit.

I have written an article on soldering basics for another forum. Feel free to take a look for tips. http://elitecaraudio.com/tips/car_audio/soldering1.shtml

To whom it may concern:

When I took my Cruise amp apart, I found that one of the power transformers had gotten hot and burned up. I gave the board to a friend of mine at TRW/Lucas to see if he could get new components, but he was unable to locate the parts.

I have two questions:
1. Why did the transformer burn up?
2. Where can I get the electronics to repair it?

Sincerely,

Kevin E. Ryan
Winona, MN

Are you sure it's a power transformer?? What model do you have? CCA part no?