Lorenfb

A lot of posted mis-information in this thread:

"However, there's going to be a percentage that have component issues."

Less than 1%.

"Then there are 2 ICs ,LM 2901, they are not really reliable when they're 20+ years old, and when you reflow solder joints they can perish"

Don't think so.

"There are , in the middle(I am struggling with memory) at least 2 electrolithic condenser, very weak.change them."

Rarely.

"Change capacitors, ICs and diodes for pennies, so there's nothing prone to fail..."

Why not change ALL the components then?

"I could easily program one of these arduino micro's and lay out a board to replace the cruise control unit in a few days if someone gets the needed data. The C++ code would be simple after the last item I'm just finishing programming."

Dream on! Remember it's a control system with feedback which can have stability problems.

"If some one could make a guide and parts list to properly replace known problem part that fail that would be amazing and the easier option."

Most as can be observed from this thread, don't have any idea.

Bottom line: The simple approach is to order a rebuilt unit from 928 International.
They stock and warranty them. Additionally, many don't know how to troubleshoot
the cruise control system and verify whether the cruise control unit is truly the problem.

kevinr

Try the PCA Cayman Register and PCA Boxster register. I have an '06 Cayman S, and there are true experts on that forum (caymanregister.org and boxsterregister.org). On the Cayman forum especially, I've read detailed articles where folks have heavily instrumented their CS's to try track down earlier engine oiling system weaknesses and others that track down the root cause of rod bearing failures -- all using data and actual logic.

They also have a very low tolerance for bad online behavior. Because its a PCA forum, there's no commercial representation however -- so no one like Roger, sadly.

[...and now back to our regularly scheduled programming.]

Lorenfb

"I've read detailed articles where folks have heavily instrumented their CS's to try track down earlier engine oiling system weaknesses and others that track down the root cause of rod bearing failures"

Really? Sounds like more of the typical hyperbole found on the internet.
Ah, maybe some kind of AI system that can communicate with a mechanical system.

jcorenman

If you haven't taken the garbage out, please send them to me. Thanks!

Alan

Indeed it is!

I do use and like CC systems - like anything, you can use if for the right purpose or the wrong purpose. I don't think lack of concentration is ever an option when driving a car... however concentrating on what's actually going on is more important to me than continually monitoring my speed against some arbitrarily set limits.

Alan

siscogts

LM 2901 can stand 260 C , someone not skilled can go over 260C .data taken from datasheets .
I forgot to tell that polistirene capacitors are not very happy with heat, so germanium diodes and transistors.I usually put a crocodile clip as a heat sink between the component body and the solder pin.
about the reliability of 2901: if a capacitors is not more able to smooth varying current flow , LM 2901 can go.

changing them with the other components prone to fail( sorry,prone to age and/or perish) for some euro I think it's good.

despite the other components used on the CC brain, those components are not so easy to be checked with a common multimeter...



I repaired 7 friends cc brains (BMW VDO), plus a ot of ecus and instrument clusters of many bmws(VDO Hella or Siemens)....Always found that VDO used FRAKO capacitors for a very long time.They were always very out of spec or they were pretty gone. my previous post was wrote down by my experience.In my experience I can be sure that capacitors in the VDO cc brain are no exceptions.

1 Why not the car?
seriously, I will never buy a cow cause I want to eat a steak.

there are otu there a lot of tutorial about the gain of changing parts I said before, a lot in german( Google translate better than I was supposed to know) and some in a correct english.
following those tutorials and getting better experience with a solder:For mt it's the suggestion and the key to self repair a cc brain like that.

I agree......




I observed that you have a lot of experience, I am pretty sure you are able to troubleshoot also...and you could make a guide .It takes time to understand electronics for a lot of guys , here , me included.
So you tell what to do, and we do that.
you :the mind and we: the arms.

Ian S4

My CC module is a little different from the one pictured earlier in this thread. The "Set" (i.e., accelerate) function worked, but it would not hold any speed. Traced the fault to a short-circuited electrolytic capacitor, one of the two round "cans" near the center of the board with "FRAKO" on top. I replaced both.

Hold On

I have an 83S and I have three cc units in my garage. All three are possessed and will work or not work at will. I have opened them all up and inspected for anything looking bad or solder breaks. I have attempted to resolder and reflo. As of this morning, my cruise does not work at all. Last week it worked but would only accelerate when I hit "set" That was entertaining. Last month it worked like a charm for a few days than began to spin its head around and spit pea soup !!

JamesDean

EDIT: It just occured to me that it is 2015 now and not 2014! This thread is much older than I originally thought!

Hello All,

I'd like to introduce myself. My name is Kris and I've been repairing cruise control amps for Mercedes cars for about three years now. These cruise amps were made by VDO. Mercedes used the same VDO built cruise control amps that your cars do.

I actually just completed a repair for a 1986 911 last night. The amp is now fully functional.

I run www.CruiseControlRepair.com and to-date have repaired over 500 cruise amps from a number of Mercedes. I would like to extend my repair skills and support over to Porsche owners as well. I keep my prices low as this is more of a hobby and a way to help enthusiasts. At of today I only charge $60 plus shipping for an amplifier repair. I believe I am considerably cheaper than most places.

Your cars employ a 10-pin amplifier to control a vacuum servo. Mercedes used this same system up until 1981 or so. I believe Porsche kept it until 1989.

The most common problem with these system is cold solder joints and failed capacitors.

If anyone is interested in some photos of my work I would be happy to provide links, etc.

If there is anything I can do to help out please let me know. Drop me an email or PM on here and we can go from there. I know I don't have any posts on here but you can look me up (JamesDean) on PeachParts (owned by Pelican) or BenzWorld or 190Rev and see that I've been doing this for a while.




Cheers!

-Kris

ROG100

Hi Kris - welcome to Rennlist 928 forum. Email sent to you. Roger

Fogey1

Hi, Kris. Welcome. And yes, new photos for the archives are always welcome.

Will

syoo8

Hi Kris.

I have two busted CC amplifiers... I'll be sending one to you soon!

yardpro

Funny that they are the same as MB.
My parents had several MB's when I grew up and none of their cruise controls worked either.

The local guy told us that it was unusual for a MB with over 30k to have one that worked