Cruise amp repair - Page 2 - PeachParts Mercedes-Benz Forum

WD8CDH · #16 01-20-2009, 10:09 AM

The '81 thru '93 with 14 pin connector store the speed digitally in a counter IC. I have yet to find a schematic for any year. They seem to be a little more reliable than the earlier 11 pin analog CC amps but not by much. They are not interchangable.

Dionysius · #17 01-20-2009, 03:02 PM

Am I correct in assuming that VDO is the designer and manufacturer for this PC board - both versions (the analog and the digital)??

mplafleur · #18 01-20-2009, 09:35 PM

I'd have to believe most failures are due to overcurrent draw from bad motors, bad caps, and corrosion/bad joints. Not necessarily in that order.

lowriderdog37 · #19 01-21-2009, 07:26 PM

I am working on a schematic now. I only knew about the 14-pin, so we will be tackling that for now.

All in all, I am hoping it's just caps. It would be pretty easy to swap them out.

Again, with the 14-pin, the failure does one of two things. Doesn't catch the current speed when you flip the switch, and will speed up if you hold the switch down. The other makes the car speed up quickly when you flip the switch. I have only seen that once, and come to think of it, it might have caused the amp to fail when it did. Who knows...I really don't remember the sequence of events as it was a while back.

Anyways, for now I am working on more background info.

ksmmspt · #20 01-22-2009, 08:20 AM

PM sent. Put me in line when you feel like you have a grasp on the fix. Thanks!

rhodes2010 · #21 01-22-2009, 02:34 PM

Quote:

Originally Posted by Dionysius

Electrolytic capacitors will fail with age - they are prone to a leakage failure mode effect. When people claim they 'fixed' the board by soldering every land what they have really done is just touched the electrolytic lands with a hot iron and rejuvenated them with heat shock but this is a temporary fix IMHO. These caps were manufactured circa 30 years ago in a process inferior to what we would have today. You may find that not all have failed but my posit is the heavy hitter one which serves as the 'memory' in this ancient analog design is the one that is giving the major symptom. This circuit can be restored to its original and very fine original functionality. I admire you for looking at this and I will help where I can. The other caps act as filters (I am having to make assumptions here since I have no schematic) and their failure or partial failure could cause hunting and weird secondary effects. Note that these caps are polarity sensitive. And yes, you should replace all of the electrolytics. The other components are probably ok.

Would it be reasonable then to begin with a parts list of acceptable current off-the-shelf replacements. Like we do for the clocks ?

I have 3 (and counting) not-working amps for W123. I would love
to try and replace aforementioned caps as an experiment.

Would it be difficult to list specs for these caps ?

mplafleur · #22 01-22-2009, 05:10 PM

When you say flip the switch, do you mean setting the cruise speed by hitting the decel or accel switch?

When you do this, you capture the voltage generated by the speed sensor circuit on capacitor C19. This one is the most likely to be bad. It's the .1uF electrolytic standing up in the far corner next to the rectangular .2uF cap.

colincoon · #23 01-22-2009, 05:16 PM

I think my circuit board is fried on mine, it's warm to the touch at all times. I took a cell phone shot of the back of it, but I'm pretty sure it's fried. You tell me though, I have no idea, I'd be interested in this as well if it looks repairable! I'm fearing for the worse though...

lowriderdog37 · #24 01-22-2009, 09:46 PM

You definitely fried something in there. How about a shot of the other side? That is different from the one I have in my car, so I wouldn't be able to test it. At this point though, it's impossible to tell if you just blew a resister, or what...let alone if it destroyed anything else in there.

lowriderdog37 · #25 01-22-2009, 09:50 PM

Quote:

Originally Posted by mplafleur

When you say flip the switch, do you mean setting the cruise speed by hitting the decel or accel switch?

When you do this, you capture the voltage generated by the speed sensor circuit on capacitor C19. This one is the most likely to be bad. It's the .1uF electrolytic standing up in the far corner next to the rectangular .2uF cap.

That's exactly what I mean. I am going to start x-shooting as soon as I get one of the fried amps in. I have a few people sending me test dummies already, I just have to get home early enough one of these days to check the apartment office for a package.

Thanks for the pointers. I haven't been able to take a look at any of that info yet. It's been a busy week.

colincoon · #26 01-23-2009, 12:38 AM

Quote:

Originally Posted by lowriderdog37

You definitely fried something in there. How about a shot of the other side? That is different from the one I have in my car, so I wouldn't be able to test it. At this point though, it's impossible to tell if you just blew a resister, or what...let alone if it destroyed anything else in there.

I'll get behind the glove box this weekend and try and get another shot of the front with a proper camera. I had a hard time pulling it off of the wires connected to it though, so I gave up quickly. I'll get it out though, just need a little elbow grease!

It looks dead though, and the "warm to the touch" feeling is a bit concerning as far as proving it's super dead.

It's in Norm, the 1980 300TD.

lowriderdog37 · #27 01-23-2009, 06:57 AM

It doesn't look like yours died like the rest of ours. Most amps there isn't any physical evidence showing failure.

It's a real pain to get in and out of there...you can't give up with anything on these cars, there is always some pain in the butt obstacle to get over.

colincoon · #28 01-26-2009, 02:25 PM

You know what, I made a bonehead mistake and that is the Climate Control amp if I'm not mistaken. I was looking at them on Fastlane, and was like "Hey...that's not a cruise control amplifier!!"

Horray, I fail. But then again, I think I know why my AC doesn't work now!!!

sidoog · #29 01-27-2009, 08:51 PM

GO TO THIS SITE REGARDING CRUISE CONTROL OPERATION & REPAIR
http://gdl-online.com/differences.html

79Mercy · #30 01-27-2009, 09:08 PM

Quote:

Originally Posted by colincoon

You know what, I made a bonehead mistake and that is the Climate Control amp if I'm not mistaken. I was looking at them on Fastlane, and was like "Hey...that's not a cruise control amplifier!!"

Horray, I fail. But then again, I think I know why my AC doesn't work now!!!

I was looking at your pic and I was thinking to myself, he thinks thats the cruise amp.