HOW-TO: Cruise Control Amp Repair 14-pin
 

Hello everyone,

I decided I'd try to fix the cruise control on my 190E and 420SEL. I figured I'd write up a how-to for all of you out there. Special thanks goes out to forum member sidoog for helpful info and tips.

APPLICATION: 1987+ All Cars that uses the 14-pin VDO unit with Coding Plug.

1. TESTING THE ACTUATOR--PART A
First we must test the actuator and make sure it is within normal operating limits:

-Locate and disconnect the actuator connect inside the engine bay
-Perform the following on the actuator side of the connection

-Get an ammeter and a 2-amp battery charger.
-Connect the ammeter in series with the 12V supply
-Connect the positive probe to PIN 4
-Connect the negative probe to PIN 5

Observe the current draw. It should be within 120mA and 160mA.
The Actuator should make an audible spinning sound.

My 190E was around 130mA with my good meter. My 420SEL/560SEL measured 200mA with a cheapo meter. I blew out the fuses in the good meter before I could test the 420SEL/560SEL.

If the actuator is within this range, you can go to the next step. If not, it has the possibility of damaging the amplifier.

2. TESTING THE ACTUATOR--PART B

Next you need to test the solenoid in the actuator. This is fairly simple. Take your battery charger, and briefly tap the positive to pin 7 while maintaining ground on pin 6.

If you hear a click, then you've passed this test.

3. REPAIRING THE AMPLIFIER UNIT

If your cruise control amp looks clean and healthy (i.e no black spots indication a servo failed and hurt something) the following has a fairly high chance of success.

You'll need to open up the unit and replace a few electrolytic capacitors.

http://i.imgur.com/CvY9ol.jpg

I ordered mine from Mouser.com. As long as you get a capacitor of the same capacitance and the same or higher working voltage you'll be fine. I ordered enough for 3 boards.
Here's my parts list:
http://i.imgur.com/nDExbl.jpg

The first step in replacing these is to clean off the coating VDO has on the back of the unit.

I used this varnish remover, it worked out pretty well. After it was done I took the board to the garage and used the air compressor to blow of the remains.

http://i.imgur.com/0gzEnl.jpg
http://i.imgur.com/kyxZWl.jpg
http://i.imgur.com/eRywel.jpg

Here's the old and new capacitors:
http://i.imgur.com/PtuOml.jpg
http://i.imgur.com/tveBNl.jpg


All replaced!
http://i.imgur.com/11hVtl.jpg

Next Step is to re-flow the solder points. This step take quite a bit of time. Its not difficult just time consuming.

You basically want to tap the soldering iron and solder to each and every solder point on the board. Don't stay more than a few seconds. Especially on the large IC chips. They're sensitive to heat. Once you've done that you should be good to go!

http://i.imgur.com/Hkbznl.jpg

On my first board I used my de-soldering iron and removed all the old solder, then re-applied new. This is a bit much as all I did on the second board was reflow the joints and it worked fine.

---------------------------------------------------------------------

Repairing 14-Pin Non Coding Plug Version ~1980-1985:


Earlier Mercedes were outfitted with these 14-pin engine/chassis specific units. They do not have a coding plug on them and as far as I can tell cannot be used on other Mercedes of the era. They do have the same pin-out as the Coding Plug variants. So testing is exactly the same.


The procedure is pretty much the same as above. Strip, Replace, Resolder.

http://i.imgur.com/7FMcGl.jpg

http://i.imgur.com/pMmK5l.jpg

http://i.imgur.com/y3kYkl.jpg

http://i.imgur.com/6EkJrl.jpg

http://i.imgur.com/JI9HVl.jpg

I've not had the ability to test this unit yet as both of my 300SD's are missing their servos and mounting brackets. I have a spare servo but no good way of mounting it for testing. So tomorrow I'm going to go to the junkyard and see about finding one so I can test.



INFORMATION ON CODING PLUGS:


According to Auto Haus AZ. The coding plugs often fail before the amplifier itself. I've not experienced this yet the 420SEL, 560SEL and 190E's plugs were all intact.

Here's some pictures in case yours is bad and you need to replace the resistors.

http://i.imgur.com/KlUU4l.jpg
http://i.imgur.com/met1Bl.jpg
http://i.imgur.com/qOJkbl.jpg


If you have any questions or comments let me know.

Repair
 

You have a lot of patience! Congrats!

Until we got the 420SEL, I've never driven with cruise control on a Mercedes.

I think Monday I'll venture out to the junkyard and try to cobble together cruise systems for my 300SDs.

If anyone is interested, I'd be happy to repair your cruise control amp. I enjoy soldering. lol.

I have a sneaking suspicion that with this, you have crossed the threshold into starting a new business. You might not be aware of this yet.

You have now:
1) fixed the LCD temp readout, a perenially malfunctioning item in almost all the older MBs still on the road
2) fixed the cruise amp, another common problem

Not only have you successfully repaired these items you have shown the rest of us how. It doesn't seem like it's particle physics either! Brilliant!

There used to be a guy on the left coast who did this stuff, General Development Labs. I don't know if he does it anymore, who knows. At any rate, this kind of repair is in demand.

Next, you should try to figure out the CCU pushbutton unit! There's one for you. Although a common pattern I'm seeing is that it's those caps giving up the ghost every time.

You should throw a simple web page up and advertise repair services for this stuff. I'm sure there are a lot of units out there needing some similar repair across all makes of European autos. The electronics in these cars are ridiculously primitive, for a modern electrical engineer a cakewalk. Most people would sooner buy a rebuilt unit than replace individual components on the PCB.

I'd take you up on your offer to fix, but I've been lucky that my cruise amps have remained operational. I will however use your information to repair my LCD temperature readout. I like to solder too.

HVAC push button repair on Gen. I W126 would be awesome.

I bought a new one 5-6 years ago and it broke just recently. If I press the middle or second from the right button, the fan doesn't kick on. I've got to press the fourth from the left button to get the fan to kick on and then click EC or the middle button if I desire those settings.

Based on what I've read on the forums this is a common problem with the units. I got a few from the yard to try out and they all exhibited the same problem!

I've tried soldering numerous times on two different units with no success.

I'd love to try fixing a first gen 126 climate control unit. Sadly I've got no spares to work on. The ones in my 300SD's work fine.

One forum member on here has already contacted me about fixing a unit for his 124.

I think I might head to the junkyard on Monday and get a few cruise control units and see what I can do. I dont think there are any first gen 126s at the yard though.

I probably wouldn't want nearly as much as the other places to fix these. I've seen prices up to $200+.

I've been looking into the possibility of using the newer "with coding plug" style units on the older cars.

Here's what I've come up with:

The coding part sets the impulse per kilometer range for the unit (As evidenced by: VDO Catalog Tempostat Coding Plugs) This range differs from transmission to transmission it would appear. The VDO numbers on the two plugs I have don't match up to that image at all. I've cross referenced MB stuff a bit and came up with the following:

My 300SD uses a 722.303/722.416 transmission.

These amplifiers work in it 002 545 16 32, 002 545 82 32, 003 545 86 32.

These units also work in a variety of other chassis, namely the 201.122,
124.120. The 190D 2.2 and the 200D/E200 Diesel respectively, both use the 722.403 transmission.

In the 190D 2.2, the amplifier was replaced by the newer 14-pin coding plug type with plug 005 545 11 32

So there is a chance that this 005-545-11-32 plug coupled with the 14-pin newer style cruise unit could be used in all 722.303/722.416 enabled cars.

I don't have this plug on hand, and its $40 from the dealer! So if anyone has this on their car. I'd love to get a peek inside at the resistors so I can order up some resistors and test this theory out!

I a picture of mine:

https://lh6.googleusercontent.com/-2.../P08524812.jpg

The bottom "resistor" is just a straight through wire.

I don't recall what number is on my plug :(

-J

-J

Is that from your 350SDL ?

I'm 99% sure it is. It is possible it's from the 420SEL's cruise amp I got at one point, but I really don't think so.

-J

Yep. Those resistors dont match up to the V8 plug I have in the first post. Must be for the 350SD/SDL's 722.361 transmission.

Here's the FSM info on these cruise controls: http://www.startekinfo.com/StarTek/outside/12253/program/Chassis/54-500.pdf

Kris, you best purchase your bits from Mouser.com! My woman has been there nearly a decade... so going to Digikey is like a stab in the back to me! :D

I have a 1st gen unit I will mail you soon. It is a late 90s reman from Programma. The lack of low speed fan is irritating.

I found a large reference table and it looks like I can redo the coding plugs for any specific model that I need.

So far I have a 100% success rate repairing these units. I just repaired a unit for a 85 300D for 79Mercy. I've got enough spare parts to repair probably 5-6 more units if anyone is interested. Send me a PM.

I got my amp back today from JamesDean my cruise control works flawlessly, used it to and from work tonight, about 20 miles each way and it held perfect constant speed the entire time. All other functions work properly, all thanks to JamesDean!

Looks like I will mail him my SDL c-amp too. :)

How much would you charge to repair an amp?

I charge $50 for the actual repair work. Shipping is done via usps flat rate boxes, its only $5.35 each way.

I've started keeping a spreadsheet of what I've repaired. So far I've done about 5 of the newer 005 545 models with success and one of the 002 models (79Mercy's) with success.

Thanks....PMs sent.

The comment about coding plugs failing prior to the amp surprised me.

Me too. I read it on Auto Haus AZ's website. I've yet to see a failed plug. I test them to make sure they're good too.

I asked Peter at GDL about it. He said that, in 25 years of repairing MB cruise amps, he's never seen a bad plug.

So I was in the garage today looking for my MityVac to test some vacuum pods and I stumbled across a cruise control amplifier. I thought it was from my gold 300SD as its and early model and I've only ever removed one (first gens were a pain to remove).

Evidently its from a first gen v8. Part number 001 545 76 32. EPC crosses to 380 and 500 SE/SEL/SEC's.

I decided to replace the capacitors and go over it like I've done the rest. I tested it out in the testing jig and it seemed to work, so I threw it in the green 300SD and voila cruise control back.

I actually took out the green SD's cruise unit and its a different model. There are few difference between the two boards though, namely three resistors that are on raised solder points. I believe these are akin to the coding plugs of the 005 variants.

I'll post up pics later. Interesting stuff.

I was taking apart my 420SEL's cluster to repaint the needles and found this:

8075 Impulses per Mile. or
12,920 Impulse per kilometer

http://i.imgur.com/DQfk7l.jpg

This seems to agree with my original claim that the coding plug has to do with impulses and "setting" things internally for the signal type.

Based on this listing in a VDO PDF Catalog:

http://i.imgur.com/5vEakl.jpg

I'll have to pull on the of the SD's clusters and see what it says on the back of it. Probably will have to be the gold SD as the green one is a DD.

I found this on my 300SD:

K=10,240. It doesn't say miles or Kilometers. If we assume its in miles as the 420SEL was, then you get K=16,384 impulses per kilometer.

So in theory, If i sourced with the x4 or x5 one of them should get a newer coding style unit working on my SD..

http://i.imgur.com/GwyBil.jpg


If anyone has their cluster out of their car, can you let me know if you have a K value sticker on there?

None for the 124 cars?

Thanks

I have several 124 car coding plugs. I can take pictures and post, which car are you interested in specifically?

The 1991 124.030

Thanks!

Here you go!

http://i.imgur.com/XpLMVl.jpg

What do these coding plugs tell the controller?

I have used different ones in my 300E and they all seem to work....

I'm sure James can shed more light than myself, but I fully expect that the combination of resistors basically sets up the unit, for a particular gear ratio or some such.

The ignition system on the early 124 gassers works a similar way. There is a resistor that plugs into a socket near the master cylinder. The resistance provides a setting for a particular maximum ignition advance. Remove it and you get max ignition advance but premium fuel is required. Different resistances retard ignition to different levels for use of different fuel grades.

Some ROW cars have a dial in the resistors place so that you can set for different octane ratings. This is a more necessary feature in some countries were high grade fuel is difficult or impossible to obtain.

Sorry for the diversion from the thread subject.

I have a couple of questions, JamesDean. About to replace caps in one of these. See photos below, please. In one corner on the back of the board, there is some really sloppy soldering. This box had never been opened before. Have you seen anything like that? Seems like all that shellac goo they put on there would insulate the heat sinks on those transistors, preventing the heat sinks from dissipating heat? All my components are pretty well glued down to the front of the board. Does that paint remover of yours work pretty well getting the goo off? Thanks!



http://webpages.charter.net/mycamera...a/SAM_0394.JPG

http://webpages.charter.net/mycamera...a/SAM_0395.JPG

http://webpages.charter.net/mycamera...a/SAM_0398.JPG

Brewtoo,

That board looks like most of the ones I've worked on. I would be sure to touch up the solder points that you think look suspect.

The transistors are supposed to dissipate a maximum of 25W at full power, however these guys are operating at maybe 5-8% of maximum so I doubt they dissipate too much heat.

Yes the varnish remover easily removes the coating. I only apply it to the rear of the board when I do work on these as there no real need to remove it from the other side. The capacitors, once de-soldered, come out with minimal effort of the pliers.

Hope this helps! If you've got any other questions post up!

Just wanted to let you know that I replaced the capacitors in several of these units. I had several I had bought from junk yards. All dead.

Now, every single one works perfectly.

BTW, I only replaced the caps - I did not re-solder the rest of the board on any of them.

One of mine had been "refurbished" according to the sticker on it. Inside, I studied the board and the parts were all original. It appears that the refurb consisted of nothing more than re-soldering all the joints. I say that because there was a good bit more solder on these joints than on any of my other boards. Also, the shellac had been stripped and a thin coat had been sprayed back on. Anyway, it too was dead. I replaced the six caps and it works great again as well.

Thanks for your help!

Glad to be of help!

Someone shipped me in a core that had a "refurbished" sticker on it as well. It looked like someone half-stripped off the coating and re-soldered in a few spots. Didn't replace anything. I came across this same company's website and they had a price of some $300+ for that particular model!

BTW, how are you testing your units? Can they be bench-tested somehow?

Sorry I didn't see this post earlier!

Yes they can be bench tested! I've got a custom built harness that essentially is a mock-up of the in-car cruise control system. All of the components are there, I just have to provide it with power and a speed signal then test out the various functions.

I ordered the three different types for a 005 545 05 32 board. Unfortunately (or maybe not so) the 10uF caps I ordered are non-polarized. Does that make a difference? Will they work just the same?

Its OK to use a non-polarized capacitor in place of a polarized one. Its NOT OK to go the other way around, to us a polarized one in place of a non-polarized one.

So, in short, you'll be OK.

Great! Many thanks Sir.

Is anyone still repairing these? Or maybe tell me what typenof soldering iron is best for this. I would give it a shot but my iron might be to big for the board.
Thanks

Hello there! I am still repairing these. I've been a bit delinquent in replying to my pm's and emails so if you have sent me one I do apologize for the delay l. If you haven't feel free to drop me an email at jamesdean59@gmail.com and od be happy to help out.

We've had a death in the family and my regular job has been running in "crisis" mode the for past few weeks so I've just not had a lot of time to work on cruise repairs and whatnot. However, things have finally called down and I'm getting back into the swing of things.

-Kris

Thanks for your reply. PM sent.
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Anyone know if using an amp with the wrong coding plug can cause any damage?

I bought two used amps from the junkyard, both from and for W201 2.6. One was good and working, and the other didn't do anything. I put the good amp back in the car and it worked perfectly while driving to another yard. I exchanged the dead unit for one from a W124 in the next yard and tested without swapping the plug which did nothing in the car. I put the correct coding plug for the W201 on the amp and again it did nothing. After putting the good working amp back in the car with the correct coding plug now it's not working.

Happy St. Pat's. :beerchug:

The coding plugs are just a collection of resistors. In my experience swapping them around won't kill an amplifier. The amplifier in question may have been marginal to begin with. If you would like you can send the unit in and I'll test it out for you, see how its doing.

--Kris

My original plan was to just send you the original one that was in the car rather than play whack-a-mole with amps from the junkyard, but I figured I'd take a chance and buy the warranty for a few bucks which guarantees me a working unit so long as I can find one at any of the PYP's within 30 days.

Thanks for the reassurance about the wrong plug and the offer to test the unit. I'll test the actuator to take it out of the equation. Unfortunately I returned my original amp for core value that would engage for a few seconds, which would have been nice for troubleshooting, then hopefully find a working amp in a parts car. If I can't get one within the warranty period I'll send mine over for testing.

Surging...
 

Has anyone had any experience with their cruise control working, as in it holds the correct speed and everything, except it surges? It's like the throttle inputs are not very smooth. It has done this with the 2 different actuators I have tried.

Could it just be the amp giving up? I wanted to get your opinon before I cracked it open to try to repair it.

Yes. When that happened to me the cause was a bad amp.

Thanks for the info. I wasn't sure if they could fail in that manner. I guess I'll be ordering some new parts for it.

I have only once ever had a w126 module fail that couldn't be repaired by either re-soldering cracked joints, or replacing aged electrolytic capacitors.

Of particular importance when you replace the capacitors is to choose ones with the highest temperature rating possible. 105C should be the minimum temp rating for automotive use. Also, be sure to observe polarity!

Good thread, i'm in the process of getting my cruise control to work.

Hilariously, I can make the car move faster with the cruise stalk but the speed never sets which leads me to believe it's a bad amplifier.

I'm going to go to the salvage yard tomorrow to try and pick one off of a car. Here's hoping I can find a good one!