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Garage => Mechanicals => Topic started by: ptashek on 21 September 2012, 03:00 PM

Title: Cruise control not keeping set speed
Post by: ptashek on 21 September 2012, 03:00 PM
The cruise control in my 450 has some existential issues. Whenever I set the speed and take my foot of the accelerator, cruise control takes over but is unable to maintain the set speed over any reasonable distance. Basically, the car will slow down something like 5mph every mile. What might be the cause here (vacuum leak?)?
Title: Re: Cruise control not keeping set speed
Post by: jbrasile on 21 September 2012, 03:20 PM
ptashek,

A vacuum leak is a possibility but usually the control unit is what goes bad. Let me guess, it will accelerate fine when you move the lever up but will not hold speed correct? This is typical behavior of a defective ECU.

Tks,

Joe
Title: Re: Cruise control not keeping set speed
Post by: ptashek on 21 September 2012, 03:46 PM
ptashek,

A vacuum leak is a possibility but usually the control unit is what goes bad. Let me guess, it will accelerate fine when you move the lever up but will not hold speed correct? This is typical behavior of a defective ECU.

Yes, that's exactly what happens.
I have one spare from my 350, will it work with a 450?
Title: Re: Cruise control not keeping set speed
Post by: jbrasile on 21 September 2012, 07:02 PM
Yes the 350 ECU should work without any problems.

MT is right, but I just don't have the skills... hehehe, so for the 1980 450SEL I got an exchange unit many years ago from a supplier that used to advertise on Hemmings Motor News, can't remember their name but the system is still working perfectly. In the 78 car I may have a vacuum leak, just waiting for a replacement actuator to arrive from LA.

Tks,

Joe
Title: Re: Cruise control not keeping set speed
Post by: ptashek on 22 September 2012, 02:25 PM
That's great news. I have no problems with electronics, and there probably isn't anything surface soldered inside those ECUs considering their age. That should make things easy.
I'll give that 350 unit a try, and if that doesn't help I'll rebuild both. Heck, while I'm at it I might ask some electronics-ninja if the unit could be emulated with something more modern.
Title: Re: Cruise control not keeping set speed
Post by: oversize on 24 September 2012, 04:49 AM
And this is exactly why I won't buy a later MB unless it's under 10YO!!!  How much is a replacement ECU on a W140 anyway??  $1500...  $2K....  $3500??   :o :( ???
Title: Re: Cruise control not keeping set speed
Post by: ptashek on 22 October 2012, 05:43 PM
Right, so I've hooked up the spare unit and it's an even bigger dud then the one I already have. It's proper dead.
I've taken a pic of each side of the PCB, layered the two in Photoshop with a few small tweaks and am working on reverse engineering the thing as far as the schematic goes.
I wonder if this whole pile of junk could be replaced with a MC14460 IC (and if it is still available). It's an almost complete cruise control unit in a single chip.  Looking at its datasheet (PDF) (http://www.datasheetarchive.com/dataframe.php?file=DSAP0010176.pdf&dir=Datasheets-110&part=MC14460P#), it seems doable at least in theory.

Here's the board from my 350SE:
(https://s3.amazonaws.com/MB450SE/docs/cruise_control.jpeg)
Title: Re: Cruise control not keeping set speed
Post by: navigator on 31 October 2012, 04:47 AM
Where does does this ECU live?

I have same problem with my 350
Title: Re: Cruise control not keeping set speed
Post by: ptashek on 31 October 2012, 08:51 AM
Where does does this ECU live?

I have same problem with my 350

It lives just beside the steering column under the dash, at least on RHD models. I guess it's mirrored in LHD. Getting to it is not much of a problem - just unclip the panels. Getting it out is a bit trickier, as there's very little space to get your hands and a wrench in.
Title: Re: Cruise control not keeping set speed
Post by: navigator on 01 November 2012, 04:53 AM
Thanks!!
Title: Re: Cruise control not keeping set speed
Post by: ptashek on 15 December 2012, 12:29 PM
This is one of the best cruise control finds thus far...
The whole thing described properly: http://userweb.windwireless.net/~jimc/vdocc1/vdocc1.html
...and troubleshooting steps: http://userweb.windwireless.net/~jimc/mamerepairs.html#cruisetest
Title: Re: Cruise control not keeping set speed
Post by: ptashek on 31 January 2013, 09:36 AM
OK, so I've finally replaced all the caps on my board, now it keeps the speed but surges a lot.
I guess next step is to re-solder all the joints?

One new find - the Motorola quad-comparator chip next to the Siemens TAA765A op-amp was replaced at some stage, between March 1977 and June 1979 (dates on my modules), with a LM2901N (datasheet (http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00000532.pdf) [PDF]). While the Motorola is almost impossible to get, the LM2901N is readily available for a few cents.
Title: Re: Cruise control not keeping set speed
Post by: oversize on 31 January 2013, 02:10 PM
It's it great that these things are repairable?  Love your work!   :)
Title: Re: Cruise control not keeping set speed
Post by: ptashek on 31 January 2013, 04:52 PM
It's it great that these things are repairable?  Love your work!   :)

It is!

I haven't really done much, beside following existing advice on this and other sites, and sharing what I have found myself.
Compiling all the data, these are the things to check:

- cc amplifier - I'm quite sure mine is in good shape now
- throttle actuator - unlikely, as it does work (as in "pulls the throttle")
- throttle linkage - unlikely, it used to stick but has been well greased since and just works
- speedometer cable - if it is stretched or worn, the needle would wobble making the speed reading inaccurate (mine wobbles slightly at ~50mph)
- speed sensor - ties in directly to the above, as the sensor reads speed off of the cable and feeds it to the CC amp
- vacuum leaks - more than likely given that my central locking works for about 5 minutes after engine shutdown, then all the vacuum is gone

The surge is by about 5mph above set speed, e.g. if I set the CC to 60mph it'll go 60-65-60 all the time.

Are there any household methods to test for vacuum leaks?
Title: Re: Cruise control not keeping set speed
Post by: ptashek on 02 February 2013, 06:43 AM
More updates from the CC repair front...

Quote
- throttle actuator - unlikely, as it does work (as in "pulls the throttle")
- throttle linkage - unlikely, it used to stick but has been well greased since and just works

I've taken the air filter box off today, and have cancelled almost all slack on the actuator linkage before running out of thread on the adjustment screw. The surging is still there, but far less, so a partial win on that front. I guess this is what I need to look more into. Does anybody know if the actuator cable is a replaceable part, or do I need to replace the whole unit? Other option is to cancel the slack by shortening the cable and re-terminating it.

Quote
- vacuum leaks - more than likely given that my central locking works for about 5 minutes after engine shutdown, then all the vacuum is gone
Need to get my hands on some vacuum testing equipment. This is still a likely cause.

I've also taken the car for a test drive on a motorway today, hit the CC stalk at ~60km/h and released it at 100km/h ("accel set"). The car kept accelerating up-to 120km/h, then just let go and did nothing until the speed dropped to ~90km/h, at which point it was trying to maintain that speed. Interesting. Why would it keep going after releasing the  CC stalk, and why would it store a speed ~10km/h less than actual? Could this point at invalid speed data supplied to the CC amp, and hence problems with the spedo cable or speed sensor?

I'm not giving up on this one :)

Below is a shot from my engine bay showing the location of the adjustment screw. Keep in mind this is a RHD model, so if you drive a LHD model element locations are likely mirrored. Click the image to see the full-size version.

(http://s3.amazonaws.com/MB450SE/repairs/cc_actuator_linkage_t.jpg) (http://s3.amazonaws.com/MB450SE/repairs/cc_actuator_linkage.jpg)
Title: Re: Cruise control not keeping set speed
Post by: ptashek on 02 February 2013, 10:44 AM
The Mercedes-Benz crowd should really do a reality-check, or maybe visit a shrink... or both. They're selling new CC amp units (http://wiki.mercedes-benz-classic.com/index.php/A0055451232/en) for 817EUR. I mean, there's like 50EUR of parts worth in there (including the ICs), the PCB is dead-simple and cheap to make on an industrial scale...

A replacement actuator is half-that price (http://wiki.mercedes-benz-classic.com/index.php/A0015450732/en). Not cheap either, but it's a part that one can't just make themselves at home, unlike the CC amp.

I don't get those guys. At all.
Title: Re: Cruise control not keeping set speed
Post by: ptashek on 03 February 2013, 07:51 AM
Does anybody know if the actuator cable is a replaceable part, or do I need to replace the whole unit?

To answer my own question: the cable is a standalone part, sadly NLA.
Part number is A1163002230.
Title: Re: Cruise control not keeping set speed
Post by: oversize on 04 February 2013, 01:52 PM
I'm sure you could have the cable repaired (and shortened) by any company that makes custom accelerator cables
Title: Re: Cruise control not keeping set speed
Post by: ptashek on 04 February 2013, 02:21 PM
I'm sure you could have the cable repaired (and shortened) by any company that makes custom accelerator cables

It's an easy DIY job, provided I can heat the terminating barrel enough to get it off and then back on the cable.
Looking at the cable itself, I'd say I could make one from bicycle brake parts as long as the shield is thick enough.
The problem is the plastic adjustment screw which gets brittle with age, so much so that the one on my donor disintegrated when turned with nothing but fingers.

But I think my ultimate problem is (still) with the amp and most of all vacuum leaks. My central locking keeps vacuum for 2 open/close cycles, but no longer than 5 minutes - and that's hooked up to the same reservoir as the CC is using (the one in the trunk). I have new membranes coming in from Mercedessource any day now.
Title: Re: Cruise control not keeping set speed
Post by: oversize on 04 February 2013, 02:35 PM
I'd sort your vac leaks first.  But they'd be unlikely to cause the car to accelerate beyond the set speed
Title: Re: Cruise control not keeping set speed
Post by: Tony66_au on 04 February 2013, 06:02 PM
I actually toyed with the idea of buying a VDO Cruise control unit and retrofitting it to the SEL which doesnt actually have CC and using the speed sensor unit that comes with the VDO unit if I cant adapt the signal from the rear of the speedo.

I think that short of cleaning the board and replacing all the 30 year old components its always going to give some trouble be they dry joints or devalued componentry PLUS the external push/pull pots could arguably be far better replaced with new aftermarket units.

I did pull down the old unit from my 450SE and showed it to a Russian bloke I used to use for board level stuff (Who worked on the Russian Space program in the 60's weirdly enough) and he said he could remanufacture it but there were better and cheaper ways to go.
Title: Re: Cruise control not keeping set speed
Post by: jbrasile on 04 February 2013, 07:00 PM
Guys, cc amps are available rebuilt from George Murphy at Performance Analysis (http://www.perfanalysis.com) for a fraction of the cost or you can also get them from General Development Laboratories (http://gdl-online.com/begin1.html), I have had one from GDL installed in my 1980 450SEL since 2002, still functions perfectly.

Tks,

Joe
Title: Re: Cruise control not keeping set speed
Post by: powerglide on 07 February 2013, 04:38 PM
Oversize has a really good point: I have a W140, and you cannot afford any OEM parts from DB - they buy from outside suppliers and re-price simply moving the decimal point to the right.  Makes Jesse James and Ned Kelly look honest. Look after your W116 - they're not making any more of them, and good examples just aren't around any more.  Even W126s are drying up, and they just aren't the car the W116 is.  The W140 is a really good car, but you do have to hunt for parts at affordable prices.  On the other hand, it is simply a FABULOUS car.  The cruise works just the same as in the W116 and it works the same as in the latest C series, but of course who knows what microchip horrors are underneath in the later cars?  The word is, if you want a modern MB that is reliable and won't bankrupt you to own, get a Lexus. They have cruise and all ...
Title: Re: Cruise control not keeping set speed
Post by: ptashek on 07 February 2013, 07:14 PM
A few more notes from the front. Having replaced all the caps on two units, I can safely say there's no point in touching the larger polyester-film ones. The only ones gone dodgy between my two boards was  a 10uF 16V, and two of the 0.01uF 100V. The electrolytics were of course total toast (max 20nF charge on a 47uF cap...). Probably next thing I'll do to one of the units will be replacing all the ICs (~20EUR in parts) and the transistors (should be <10EUR).

Below is a list of all the caps, just for reference (since MT's post is gone).

Polyester-film (10% tolerance)
1x 10uF 63V "big Bertha" ;)
3x 100nF 250V
4x 150nF 100V
1x 100nF 100V (axial)
1x 1.5uF 25V
2x 2.2uF 35V
1x 15uF 10V
1x 100nF 100V
1x 4.7uF 10V
1x 10uF 16V
1x 47nF 160V
2x 4700pF 400V
2x 10nF 100V

Ceramic
2x 68pF

Electrolytic
2x 47uF 16V

Keep in mind, that the voltage bit doesn't need to be exact if you can't find a replacement. As long as the capacity is same, and the voltage rating equal or higher than the original, it's OK.
Title: Re: Cruise control not keeping set speed
Post by: ptashek on 15 March 2013, 06:47 PM
Well, gents, I can now report full success in getting my cruise working again!
This was one of those non-trivial cases, where multiple things combined.

0. Door locks got new diaphragms; main heater valve got replaced - this solved most of the vacuum leak problems (some still persist). Also, the actuator cable slack was cancelled.

1. The cruise control unit was not keeping speed because of the two dried out 47uF electrolytic caps - these got replaced first.

2. Once #1 was done, the unit was surging like crazy and still losing a few mph every few miles (hard to notice on short distances) - all caps got de-soldered, tested and replaced. In total 15 got replaced, but all bar one didn't really need to be. More on that below.

3. With #2 out of the way, there was no surging any more, but still some speed loss.

4. All major components got replaced with new parts - TAA765A (op-amp), LM2901N (quad-comparator), BD437 (power-transistor) and BSV81 (IG-MOSFET)

5. All major joints have been re-flowed (not all, as I was fed up with soldering at that point).

It cost me €70 in total in terms of parts, and only because I was rebuilding two units and some components had minimum order quantities. The other unit is as dead as it gets despite all the work (relays).

Some observations made along the way:

- Surging is most likely caused by two things - the power transistor (the one stuck to the housing) is probably burned out, or close to. This points at two things - poor cooling, and/or to much power draw from the actuator. Poor cooling is due to daft design by VDO (plastic as radiator, really?). Replace the transistor even if it's OK. In my 1979 unit this was a BD437, which costs about €0.44. The 1977 unit had a 2N5190, which is about €3.20.  If the actuator is drawing to much current from the amp the power transistor will burn out quickly, so look for a working actuator. You're in for some big expense - new units are available but cost in excess of 400EUR.

- The polyester film caps are rock-solid despite their age. The ceramic 68pF caps are good as well. I've tested all on both my units and had just one dud (the 4700pF 400V one). I've only replaced some of mine because they were dirt cheap.

- If your unit does not engage at all (no response to CC stick), it's most likely one or both the relays. Good luck finding replacements...

- Do not replace the polyester film caps with electrolytic ones.

This is how my unit looks like post-repair. I still need to find a way to cool that power transistor properly.
(https://fbcdn-sphotos-b-a.akamaihd.net/hphotos-ak-prn1/883851_630213280325927_768918095_o.jpg)
Title: Re: Cruise control not keeping set speed
Post by: ptashek on 17 December 2015, 02:40 PM
Prompted by revilla, I've done some more digging on the two relays on the amp board.

AZ1530-08-101 - American Zettler sealed version from A530 series, 12V DC SPDT, 9V/>600mV DC pull-in/drop-out voltage, 1A switching load

Günther 33001176071 -  Günther 33 series, 12V DC DPDT, normally open; 7V/1.5V DC pull-in/drop-out voltage, 0.5A switching load
Title: Re: Cruise control not keeping set speed
Post by: ptashek on 17 December 2015, 02:42 PM
Also, the AZ1530-08-101 may be either a 1A, or 10.1A or 101A... it's unclear from the datasheet. I'm assuming 1A.
I've contacted American Zettler for some more details about this part.
Title: Re: Cruise control not keeping set speed
Post by: revilla on 18 February 2016, 01:38 PM
With a huge help from Lucas I fixed my CC.  I'm not a big electronics guy but learned basic soldering skills that allowed me to tackle the usual suspects in the PCB.

First, the 2 47uF 16V condensers.  CC came back to life but quite unstable. It randomly engaged and disengaged.  Then I re-soldered all the joints.  Things improved.  I thought (many times) problem solved.  Not quite.  After a few days CC became unpredictable again.  I few of these cycles followed (re-solder every joint, test for a few days, performance degraded).  Then one of the relays on the board (AZ1530-08-101) caught my attention as it was vibrating and making a high pitch noise.  Bought a replacement but package was different size and simultaneously I realized the original relay was not well soldered.  Fixed that problem, but still CC randomly disengaged.   At that point I decided to not just melt the existing joints but to remove the old flux and put fresh one.  Soldering skills and confidence improving, I thought. 

CC started performing better for longer periods, but still no permanent fix.  The ProGrama replacement PCB at $155 was more often crossing my mind.  Daniel in Canada reported good results on that option and I was tempted; until shipping cost quote to France gave me courage to keep looking into my old PCB. 

Then this article came across from Lucas.  https://www.dropbox.com/s/u0tz64j1x9ebwgr/The%20VDO%20Analog%20Cruise%20Control%20Module.pdf?dl=0 (https://www.dropbox.com/s/u0tz64j1x9ebwgr/The%20VDO%20Analog%20Cruise%20Control%20Module.pdf?dl=0)

Half of it was Chinese for me but I then focused on K1, K2, U1 and C19 capacitor.  I ventured one step further.  Desoldered and dismounted these components from the board, cleaned contacts and resoldered back in PCB.  Bingo!! 

CC working fine since.  Set speed in right on the spot for long periods.  I took the car for a ride 50+ Kms on highway CC engaged.  No even one glitch.

There was a lot of trial and error, but I guess it came down to bad old solder joints that I couldn't catch by eye nor using a multimeter for continuity test.

Long process yet good results.  Fingers crossed fix will last.

Hope it help others with super basic electronics knowledge like me.  As someone wrote here recently, it's all about learning new things and sharing the passion for our W116s.

Cheers
Title: Re: Cruise control not keeping set speed
Post by: raueda1 on 12 June 2018, 01:29 PM
Hope it's OK to bump this thread.  It's pretty amazing IMO.  I'm bumping cause I'm going to try to rejuvenate my CC module.  I'll report back with the results in due course. In the meantime has anybody else tried the fixes described here?

As an aside, my module had already been hacked by somebody.  The bent flanges holding the case on the plastic connector body had been unbent and rebent.  A bit of a mess.  Yet inside there was no sign of any soldering, unsoldering or anything else. curious. Maybe somebody thought they'd give it a go and then realized they were over their head.
Title: Re: Cruise control not keeping set speed
Post by: ptashek on 13 June 2018, 03:16 AM
Hope it's OK to bump this thread.  It's pretty amazing IMO.  I'm bumping cause I'm going to try to rejuvenate my CC module.  I'll report back with the results in due course. In the meantime has anybody else tried the fixes described here?

As an aside, my module had already been hacked by somebody.  The bent flanges holding the case on the plastic connector body had been unbent and rebent.  A bit of a mess.  Yet inside there was no sign of any soldering, unsoldering or anything else. curious. Maybe somebody thought they'd give it a go and then realized they were over their head.

I've rebuilt two units using all that's documented in this thread. One works near perfect, but the other needs new relays.
Revilla did a rebuild and got his unit working as well.

This thread is really just an amalgamation of multiple threads here and on other sites, combined with my own research into some of the more obscure elements.
Many have reported good rate of success following this process. The result is not always ideal, e.g my own working unit still drops speed over time, but it's still better than a complete dud :)

The only sad part is that the unit is probably rebuildable once, maybe twice.
I don't think the PCB would respond well to more (de)soldering than that.

The best way would be to reverse engineer the thing, and sell it as a self-assembly kit. Fresh PCB, parts and all. Or use a micro-controller like the Arduino.
But given modern human's tendency to sue anyone for anything, I'm not even going to try and do that with a device that can potentially have lethal consequences in a failure scenario.
Title: Re: Cruise control not keeping set speed
Post by: raueda1 on 18 June 2018, 11:41 AM
I just ordered components sufficient to do the repairs listed described above here on 5 CC boxes.  The total was only about $35.  This isn't a very high priority for me so it will be several weeks (at least) before I can get to it.  Stay tuned.....
Title: Re: Cruise control not keeping set speed
Post by: raueda1 on 21 June 2018, 01:11 PM
A few more notes from the front. Having replaced all the caps on two units, I can safely say there's no point in touching the larger polyester-film ones. The only ones gone dodgy between my two boards was  a 10uF 16V, and two of the 0.01uF 100V. The electrolytics were of course total toast (max 20nF charge on a 47uF cap...). Probably next thing I'll do to one of the units will be replacing all the ICs (~20EUR in parts) and the transistors (should be <10EUR).

Below is a list of all the caps, just for reference (since MT's post is gone).

Polyester-film (10% tolerance)
1x 10uF 63V "big Bertha" ;)
3x 100nF 250V
4x 150nF 100V
1x 100nF 100V (axial)
1x 1.5uF 25V
2x 2.2uF 35V
1x 15uF 10V
1x 100nF 100V
1x 4.7uF 10V
1x 10uF 16V
1x 47nF 160V
2x 4700pF 400V
2x 10nF 100V

Ceramic
2x 68pF

Electrolytics
2x 47uF 16V
1x 4.7uF 10V
1x 2.2uf 35v
-----------------------------
Other polarized caps:
1x 2.2uF 35V
1x 1.5uF 25V
1x 10uF 16V
First repair attempt was to replace the electrolytics above and C19 (circled in green on the picture).  Unfortunately it didn't work.  Same problem:  speed doesn't set.  Pushing 'resume' on the stalk does hold speed but only as long as it's held.

I did notice something interesting though.  There seem to be 3 other polarized caps, at least on my board, C9 1.5uf, C4 2.2uf and C18 10uf (circled in red on the picture).  Polarity is indicated on the caps themselves as well as the back of the board.  I edited the parts list above accordingly.  Interestingly however, the schematic only indicates that C4 is polarized! 

Next step will be to try to test relays and replace the power transistor Q1 (which I already have).  Depending on the result I'll likely replace those other polarized caps on principle.  I'd likely go with tantalum caps unless somebody thinks that's a bad idea.  Comments welcome of course!  Thanks and cheers,

Title: Re: Cruise control not keeping set speed
Post by: ptashek on 21 June 2018, 05:21 PM
I've not seen a board with this specific layout before. It's missing a lot of components on the right-hand side compared to the boards I've had in my hands, like the Siemens TAA765 op-amp for example, and seems to be using a radial cap where the 10uF speed reference cap sits normally.

Is the pic above after or before repair?
Title: Re: Cruise control not keeping set speed
Post by: raueda1 on 21 June 2018, 06:11 PM
I've not seen a board with this specific layout before. It's missing a lot of components on the right-hand side compared to the boards I've had in my hands, like the Siemens TAA765 op-amp for example, and seems to be using a radial cap where the 10uF speed reference cap sits normally.

Is the pic above after or before repair?
Pic is after repair.  This reference was posted earlier in the original thread:
https://www.dropbox.com/s/u0tz64j1x9ebwgr/The%20VDO%20Analog%20Cruise%20Control%20Module.pdf?dl=0 (https://www.dropbox.com/s/u0tz64j1x9ebwgr/The%20VDO%20Analog%20Cruise%20Control%20Module.pdf?dl=0) 
Very interesting reading, if you haven't seen it you'll be amazed!   It has a component location diagram and full schematics.  Among other things it describes 3 versions of the board, mine seems to be Rev. 2.  In Rev.1 there was circuitry to hold the last set speed indefinitely. They removed all the circuitry for that, so speed is just remembered while the ignition is on. 

The speed reference cap (C19) was indeed replaced.  According to the above reference it's 0.1uf though, not 10uf, and the original cap on my board was 0.1uf.

Any thoughts on the little red polarized caps?
Title: Re: Cruise control not keeping set speed
Post by: daantjie on 21 June 2018, 06:15 PM
I've not seen a board with this specific layout before. It's missing a lot of components on the right-hand side compared to the boards I've had in my hands, like the Siemens TAA765 op-amp for example, and seems to be using a radial cap where the 10uF speed reference cap sits normally.

Is the pic above after or before repair?
Pic is after repair.  This reference was posted earlier in the original thread:
https://www.dropbox.com/s/u0tz64j1x9ebwgr/The%20VDO%20Analog%20Cruise%20Control%20Module.pdf?dl=0 (https://www.dropbox.com/s/u0tz64j1x9ebwgr/The%20VDO%20Analog%20Cruise%20Control%20Module.pdf?dl=0) 
Very interesting reading, if you haven't seen it you'll be amazed!   It has a component location diagram and full schematics.  Among other things it describes 3 versions of the board, mine seems to be Rev. 2.  In Rev.1 there was circuitry to hold the last set speed indefinitely. They removed all the circuitry for that, so speed is just remembered while the ignition is on. 

The speed reference cap (C19) was indeed replaced.  According to the above reference it's 0.1uf though, not 10uf, and the original cap on my board was 0.1uf.

Any thoughts on the little red polarized caps?

Man looking at those circuit board diagrams gives me bad flashbacks of high school physics :o
Title: Re: Cruise control not keeping set speed
Post by: raueda1 on 21 June 2018, 06:27 PM
At last they can be fixed, LOL.  Now it's all sealed modules, custom chips and inscrutible communications between everything using Java or something like that.
Title: Re: Cruise control not keeping set speed
Post by: ptashek on 22 June 2018, 01:16 AM
Any thoughts on the little red polarized caps?

These very rarely go wrong, but I'd replace them on principle. Price-wise tantalum ones may be overkill for the job. The originals are polyester film, either MKT (Vishay) or WIMA. All still available in their original packages.
Title: Re: Cruise control not keeping set speed
Post by: raueda1 on 22 June 2018, 07:56 AM
Any thoughts on the little red polarized caps?

These very rarely go wrong, but I'd replace them on principle. Price-wise tantalum ones may be overkill for the job. The originals are polyester film, either MKT (Vishay) or WIMA. All still available in their original packages.
I decided to splurge on the good stuff anyway.  Enough for 5 boards, along with the semiconductors (except for Q9), was a bank-breaking US$14.06 including tax and shipping. ;D  It's unbelievable how cheap such components are.  But I still don't get the polarity thing with those caps if they're just polyester film.
Title: Re: Cruise control not keeping set speed
Post by: ianc99 on 26 June 2018, 09:37 AM
Somewhere on this (or another) thread I saw that CC was standard on the 450SELs.  I can't see it on mine.  What should I be looking for?
Title: Re: Cruise control not keeping set speed
Post by: raueda1 on 26 June 2018, 10:29 AM
Somewhere on this (or another) thread I saw that CC was standard on the 450SELs.  I can't see it on mine.  What should I be looking for?
Do you have the control stalk on the steering column above the blinker?  If you have that then presumably you have the rest.  There's a cylindrical servo device under the hood with a cable going to the throttle linkage.  The side and exact location vary depending on LHD or RHD etc.  The control module is more-or-less directly above the parking brake pedal on LHD cars.  I don't know it that's reversed on RHD cars.
Title: Re: Cruise control not keeping set speed
Post by: ianc99 on 29 June 2018, 03:09 PM
Nope. None of that stuff.  I guess I need to just rely on my right foot. 
Title: Re: Cruise control not keeping set speed
Post by: ptashek on 21 May 2020, 06:42 PM
Well, I'm at it again - this time trying to revive the VDO Tempostat 83.601 in my W124.
The amp is more integrated and uses a PIC to run the cruise control. Function wise it's identical to the old vacuum units, but uses the more modern servo actuator as found on early W126 etc.
Dried out caps and cracked solder joints are the main suspects, just as on the W116 units.

If anyone knows anything about that large ITT TMAT-724 chip, or has a datasheet handy please do share :)

(https://aws1.discourse-cdn.com/business5/uploads/mercedes_benz_club/optimized/3X/6/9/69c113a3ba14fcee72e743aeaae1ffde9cb46322_2_666x500.jpeg)
Title: Re: Cruise control not keeping set speed
Post by: UTn_boy on 21 May 2020, 08:40 PM
Lucas, do these 16bit microprocessors actually go bad? I've been repairing fuel computers in post 1986 W126 cars for a few years now.  They have several microprocessors in them, but I've never seen one go bad.  I did procure a 16 bit logic analyzer/tester, but haven't had to use it yet.   
Title: Re: Cruise control not keeping set speed
Post by: PosedgeClk on 21 May 2020, 09:36 PM
Well, I'm at it again - this time trying to revive the VDO Tempostat 83.601 in my W124.
The amp is more integrated and uses a PIC to run the cruise control. Function wise it's identical to the old vacuum units, but uses the more modern servo actuator as found on early W126 etc.
Dried out caps and cracked solder joints are the main suspects, just as on the W116 units.

If anyone knows anything about that large ITT TMAT-724 chip, or has a datasheet handy please do share :)
What makes you think that this is a PIC? I don't think that ITT ever had anything to do with PICs, and PICs weren't all that popular until maybe twenty years ago. Also, this chip does not have an external ROM, and for its age, it would likely have an EPROM with a label over the window if it were a CPU. This is probably an ASIC, and ASICs rarely go bad.

If you have already replaced all the electrolytics, the next step is either figuring out how the thing works or finding documentation that would be provided to a technician to troubleshoot the unit.
Title: Re: Cruise control not keeping set speed
Post by: ptashek on 22 May 2020, 01:56 AM
I was asking about the chip as it's new to me and I'm curious to figure out what it does, but it's not a suspect. I've just assumed it's some sort of very early PIC.

After first checks, the problem is as usual dried out electrolytic caps. All duds. I'll replace the film ones on principle too, albeit I'd be very surprised if any failed. The WIMAs are usually rock solid.

I'm using AEC-Q200 parts, most rated for at least 5000h at 125°C.
Title: Re: Cruise control not keeping set speed
Post by: PosedgeClk on 22 May 2020, 07:35 AM
The chip might be programmable, but it might be a purpose designed/built chip whose datasheets were only ever kept on paper and are buried under hundreds of feet of landfill rubbish now.

I would focus on electrolytics and not worry about the film caps unless there is a good reason to do it. The film caps might be part of an analog circuit that you do not want to risk de-tuning. Many but not all electrolytics in this kind of circuit are for power supply purposes, so you don't have to be too careful about value or tolerance. For instance, you can replace a 220uF electrolytic with a 330uF cap if you are in a pinch in those cases. If you are talking about an analog accumulator or filter though, you want your capacitor values to be spot on.

Tantalums were brought up earlier in this thread. They are far superior to electrolytics on most fronts, but there are some trade-offs. Tants hate reverse voltage and will smoke if stressed in that manner. If you run them close to their rated voltage for years on end, they tend to fail either open or shorted. As an example, some of the old Tektronix spectrum analyzers have a component that has a 16V tantalum on a -15V rail (or somewhere thereabouts, just going from memory). Over time, that capacitor fails, and you end up losing one of your oscillators, and in my case, the entire rail was shorted out which put some stress on the power supply and took out anything else needing that -15V rail. One of the preventative maintenance actions for such equipment is to remove that capacitor before it goes bad and replace it with a tantalum with a 25V rating. You are on the right track with picking automotive grade and 125°C temperature rating.

Is this module doing what I read earlier in the thread about holding the speed when the button is pressed? Knowing things like this provide great clues when taking the cover off a black box.
Title: Re: Cruise control not keeping set speed
Post by: ptashek on 22 May 2020, 08:16 AM
The failure mode on this one is different then the one at the origins of this thread (and two others since), but the reasons are the same. This one is rapidly trying to engage and disengage the internal clutch in the actuator, and that's about all it does. No attempt to drive the servo motor.

As for the film caps, the WIMAs are all still available as-is, so specs are not an issue. Where I couldn't get them in small quantities, I've gone either with Vishay or Kemet, same capacitance, tolerance and at least the same voltage rating.

I've rebuilt a few of the older amps before as well, only failing to revive one.

I need to hookup my scope to the speed signal input and see what the waveform looks like. The amp expects a square, but I've seen more of a sawtooth before replacing the hall sensor in the instrument cluster with a new unit.
Title: Re: Cruise control not keeping set speed
Post by: PosedgeClk on 22 May 2020, 08:34 AM
It would be great if you could post some photos of the waveforms and any pinning out that you do. A sawtooth off a Hall sensor on old, slow digital logic is a recipe for disaster.
Title: Re: Cruise control not keeping set speed
Post by: ptashek on 22 May 2020, 05:41 PM
This is what I have seen when testing the outside temperature display, before the hall sensor was replaced. It's the same source as for the cruise amp.
Not much of a square wave, and a lot of noise: https://www.youtube.com/watch?v=HdaPlZXIhXE

I'll do more testing once the replacement caps arrive and I can re-flow all the joints. Found a good few cracked ones.
Title: Re: Cruise control not keeping set speed
Post by: UTn_boy on 22 May 2020, 07:31 PM
Don't the outside temperature displays work off of a gas filled capillary tube mounted behind the front license plate frame? 
Title: Re: Cruise control not keeping set speed
Post by: PosedgeClk on 22 May 2020, 08:50 PM
Change to DC coupling, and maybe put a 1k or 10k resistor in parallel with the scope probe.
Title: Re: Cruise control not keeping set speed
Post by: ptashek on 23 May 2020, 03:32 AM
Don't the outside temperature displays work off of a gas filled capillary tube mounted behind the front license plate frame?

On the W124/W201 it's a thermistor.
Vishay  NTCLE300E3302SB or equivalent.
Title: Re: Cruise control not keeping set speed
Post by: UTn_boy on 23 May 2020, 07:52 PM
Don't the outside temperature displays work off of a gas filled capillary tube mounted behind the front license plate frame?

On the W124/W201 it's a thermistor.
Vishay  NTCLE300E3302SB or equivalent.

I misspoke.  My apologies.  The thermistor is what i was referring to when I said capillary.....but I know they're different in construction.  Where I was going with this is why would the thermistor need a hall sensor?  I thought all a thermistor needed in this some applications was an amplifier.  Looking through the W124 and W126 factory wiring schematics I couldn't find anything between the thermistor and the cluster aside from wiring and some connection points.  Hence, my confusion. 
Title: Re: Cruise control not keeping set speed
Post by: UTn_boy on 23 May 2020, 07:54 PM
Forrest, are you saying to add on an additional 1k or 10k resistance to a lead that already has some amount of resistance already built in, or is that for a lead with no resistance? 
Title: Re: Cruise control not keeping set speed
Post by: ptashek on 24 May 2020, 04:51 AM
The way the temp display on the W124 and W201 works is something like this:

- when first powered up (ignition hot) it shows the current, live reading

- as soon as the car starts moving, and that's determined through the speed signal fed to the unit, the last reading is memorized

- while the car is moving, a live reading is shown

- when stopped, the last live value is shown until the car moves again

They've done it this way to avoid showing innacurate values when stationary in busy traffic with a hot engine and exhaust from other cars affecting accuracy.

The hall sensor in the instrument cluster is what feeds the speed signal to both the CC amp and the temp display.
Title: Re: Cruise control not keeping set speed
Post by: ptashek on 24 May 2020, 04:54 AM
Change to DC coupling, and maybe put a 1k or 10k resistor in parallel with the scope probe.

I haven't even realised my scope was set to AC coupling on that test...
Title: Re: Cruise control not keeping set speed
Post by: PosedgeClk on 24 May 2020, 08:15 AM
Forrest, are you saying to add on an additional 1k or 10k resistance to a lead that already has some amount of resistance already built in, or is that for a lead with no resistance?
I'm assuming that the probes have resistance on the order of Mohms which looks like an open circuit to most circuits. Depending on the type of transistor logic used, you might need to load the outputs of the device under test to get realistic output from it. ECL logic generally means that there are BJTs involved which are current devices. I have designed some circuits which use LVPECL, and you have to have a load on the other side. With TTL, a resistor at the output isn't going to do as much. CMOS is yet another story. If the device under test is still in the car and he dragged a scope out there, the resistor doesn't need to be considered at all.

One way or another, I would switch to DC coupling because that plot is a classic example of looking at a slow square wave with AC coupling.
Title: Re: Cruise control not keeping set speed
Post by: ptashek on 24 May 2020, 08:46 AM
@PosedgeClk Were you around when I was taking on this project?

https://forum.w116.org/mechanicals/reverse-engineering-the-bosch-k-jet-ignition-module/

Djenka018 helped immensely at the time, and we can always use an extra experienced brain. My electronics knowledge is limited to what I've learned in high school years ago. I'm a software guy :)
Title: Re: Cruise control not keeping set speed
Post by: UTn_boy on 24 May 2020, 02:39 PM
The way the temp display on the W124 and W201 works is something like this:

- when first powered up (ignition hot) it shows the current, live reading

- as soon as the car starts moving, and that's determined through the speed signal fed to the unit, the last reading is memorized

- while the car is moving, a live reading is shown

- when stopped, the last live value is shown until the car moves again

They've done it this way to avoid showing innacurate values when stationary in busy traffic with a hot engine and exhaust from other cars affecting accuracy.

The hall sensor in the instrument cluster is what feeds the speed signal to both the CC amp and the temp display.

What you say about the thernistor makes perfect sense......but in a previous post you stated "This is what I have seen when testing the outside temperature display, before the hall sensor was replaced. It's the same source as for the cruise amp. Not much of a square wave, and a lot of noise."   This made me think you were saying that the hall sensor was somehow tied into the outside temperature thermistor. 

Forrest, thank you for the explanation.  Thankfully, most of what I do requires DC coupling so I never change that setting, but again the AC coupling setting could most definitely causes Lucas's odd wave form issue. 
Title: Re: Cruise control not keeping set speed
Post by: PosedgeClk on 25 May 2020, 09:46 AM
@PosedgeClk Were you around when I was taking on this project?

https://forum.w116.org/mechanicals/reverse-engineering-the-bosch-k-jet-ignition-module/

Djenka018 helped immensely at the time, and we can always use an extra experienced brain. My electronics knowledge is limited to what I've learned in high school years ago. I'm a software guy :)
I was not around at that time. I am not an expert on analog circuitry but occasionally dirty my hands.
Title: Re: Cruise control not keeping set speed
Post by: ptashek on 25 May 2020, 02:59 PM
I've rebuilt the W124 amp today, it worked twice partially, then failed the same way again. Back to the drawing board with this one.

At least the speed signal is clean as a whistle now.
Title: Re: Cruise control not keeping set speed
Post by: ptashek on 05 June 2020, 04:34 AM
I've thrown the VDO junk amp in the proverbial bin, and decided to build my own. Because ain't nobody telling me I can't :)
If you don't hear from me in a few months, please check the nearest ditch...

Quote
The “thing”. An Arduino Nano Every as the brains, and a VNH7100BAS automotive-grade half-bridge controller, to manage the simulated actuator, which is made up of a micro 12V DC motor and a 10kΩ potentiometer. Plus a lonely NPN transistor to drive the simulated wheel, and a tiny hall sensor to simulate the instrument cluster speed feedback sensor. The half-bridge controller is capable of driving up-to 15 amps of continuous load at 28V max supply voltage, without need for active cooling. Thermally speaking, it won’t even notice the VDO actuator load (a measly 1.5 amps peak), so no derating curves to worry about etc.
(https://aws1.discourse-cdn.com/business5/uploads/mercedes_benz_club/optimized/3X/f/1/f1d716f477971b88a298748d30833f801905dfb1_2_999x750.jpeg)