Somedays it is good and some days it is bad. After reading online it seems that this symptom is usually caused by the amplifier. The question is, what is the common failure of the amplifier? Is grounding the first thing i should be checking (or change the grounding alltogether?)or is there some common area that the amplifier usually fails on?

Thanks!

Two most common failures are capacitors on the board and failure in the solder joints. Other failures can be connectors and actuator. I tried to fix mine as well as one on the donor car and was unsuccessful. JamesDean is the resident expert and fixed mine so it works perfect.

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Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica

Ya, bad caps. Easy to fix if you are familiar with soldering. When replacing, only uf rating is important. Voltage rating just need to the same as original or higher. Most are over-rated anyway.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

Tantalum caps go bad over time (usually tan, pear-shaped). They were widely used as bus terminators on PC motherboards so people worried about the life, but most PC's get replaced within a decade anyway. Cars have a much longer useful life. Electrolytics (cylindrical cans) can last longer if they don't see heat, but have liquid inside that can dry up. Ceramic are a better choice today, but most are surface-mount.

The under-hood actuator also gets erratic. People here have opened then and re-greased to good effect. I have mine off now so need to try that.

No rush for me since I rarely use cruise control, even in my newer cars where it works fine. I don't like the "run-away train" feeling. Wonder how I'll feel with the new driver-less cars, or even modern cars that can be hacked to affect brakes, accelerator, and steering. I prefer direct control of those mechanisms, but perhaps I am getting old.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

but if the caps were to go bad... why would the cruise control sometimes work?

The fact that it seems erratic would suggest something is loose/ground needs work. If a cap was bad.... i would assume the effect would be black or white (still work.. or never work).

They don't normally fail catastrophically (unless of course the magic smoke that makes them work gets out ) They start to dry out and become unreliable and become affected by heat, load and other environmental factors.

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Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica

Ambush - I agree with you. In my '81 300SD I notice that I can turn on the cruise and nothing will happen; then maybe five minutes later, magically it comes on and works fine from that point forward. So is it heating up and some metal is expanding to make good contact or what?

In the case of a bad solder joint, yes, heating can cause a bad connection to connect temporarily. In the case of old capacitors, heat can change the capacitance just enough so that the circuit will start working.

One additional note is that later cruise controls (late 124 and into 210, for example) seem to be more reliable. In part that is obvious—they are newer than stuff from the 123 era—and the rest is due to real improvements in the design and construction of the electronics.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

Times two.
I've had several repaired and am a satisfied customer.

Jim

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14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles

Those cruise amplifiers are just naturally flaky as they age. To test for intermittency get a known working one to test with. Intermitents can be tricky. For example if you sent that one out for reconditioning and it performed the same after. One would wonder if the rebuild did not catch the fault or it is something else.

We used to use thermal techniques to deal with intermittents a lot. Cold spray in a can was one our favorite tools. Personally I was never a lover of any European electronic fabrication. From the perspective of gambling. Chances are it is probably the amplifier.

Thee are two after market cruise Control systems the forum members have used successfully.
The Audiovox-ccs-100 and the Rostra Global

The Official Audiovox CCS-100 Install Thread

Rostra Global Cruise Install Thread

Instead of messing around with the old MB units, this might be the way to go for you.

Charlie

sent from my pos computer

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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

Figured I would weigh in too.

Most of them its cold solder joints that cause the intermittent behavior. Especially on that 14-pin connector. That area of the circuit board is not conformal coated.

I replace the electrolytic capacitors as part of my standard procedure to help extend the life. Sometimes they are bad other times not.

I have never seen any failed tantalum capacitors. So I've not bothered replacing any of them. Now in my audio gear tantalum caps get replaced, especially if they are in the audio signal path.

I'd be happy to help out if anyone is interested. I only charge $70 for an amplifier repair, any testing I do is free. Feel free to drop me an email. All things being equal, I think you'd be hard pressed to install an aftermarket system for under $70.

I've got nearly 70K on my repaired 005 545 05 32 unit in my 300D. Originally done around 2012 when I bought the car.

-Kris

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Cruise Control not working? Send me PM or email (jamesdean59@gmail.com). I might be able to help out.
Check here for compatibility, diagnostics, and availability!

(4/11/2020: Hi Everyone! I am still taking orders and replying to emails/PMs/etc, I appreciate your patience in these crazy times. Stay safe and healthy!)


82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
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