Cruise Control - PeachParts Mercedes-Benz Forum

Dewhite2485 · #1 12-26-2007, 10:22 PM

Well I thought I had the cruse fixed, took the servo apart and it was trashed inside so I got another used one and was able to make 1 good one from the parts, motor moves, ohms correctly, solenoid pulls in, pot reads as it should threw the scale, so it should be in working order. so then I checked the switch on the, it all works as it should, so I moved on to the amp and I found a couple problems in there, I found 2 resistors so far that are toasted. What I need is some one that has a amp thats not toasted where mine is to tell me what the color bands are supposed to be on the 2 toasted resistors you can see the 2 in the picture I posted

Dewhite2485 · #2 12-27-2007, 11:41 PM

well I think I got it figured out on my own, one is brown green brown, and the other is brown black brown, I replaced them both and now it does work but at speed its jurkey it will speed up slow down speed up slow down so Im not sure if I have a dirty/poor signal from the speed sensor, a bad cap or another component thats floated from its valve, if I have a high resistance solder joint, or my other thought when I cleaned and rebuilt the cruse control actuator if the some of the grease got in the variable resistor and it just needs to wear off
any thoughts at to what I may need to do ?

dieseldiehard · #3 12-28-2007, 12:56 AM

Those resistors don't (didn't) look toasted to me, I think you are seeing the varnish used for waterproofing has discolored. Did you read the resistors on a Ohmmeter before replacing them?
The resistors that usually fail are really burned and they are at the dc input to the module and have a capacitor to ground, that cap tends to short then it draws excessive current thru the series resistor, which as I recall is a 10 Ohm resistor and it gets charred.

Troubleshooting this sort of thing is difficult without a lot of test equipment on a workbench. I usually send my modules to General Dynamic Labs (GDL) for verification before I open one because if it does go to them later they may refuse to accept it if the seal was opened and it was "messed with".

see this thread:
Cruise Control - Hesitations

Dewhite2485 · #4 12-28-2007, 08:22 AM

the one that has the case blown open in the picture was for sure bad it was it was almost a dead short, and the other with the side burnt you can see in the picture is was open so it was also bad. I have plenty of electronic test equipment O-scope, frequency counter, function generator, variable power supply, bench top multi meter, cap meter, soldering station, desoldering equipment, a few draws of new parts, and a box full of old boards for spare parts. So testing and repairing things shouldnt be to much of a problem just takes allot of time with out a schematic

dieseldiehard · #5 12-28-2007, 07:35 PM

OK, I see the one with a cracked body, I take back what I said about not overheated, its clearly been overheated!
hmmm I wonder if there isn't something else shorted?
I've heard that a shorted actuator will cause a failure on the module board. I would suspect the cruise actuator too. You could snag a module off a wrecked car at a junkyard cheap and try it, but if the actuator is shorted then it too might get damaged.

Dewhite2485 · #6 12-28-2007, 07:44 PM

the actuator that was on the car to begin with looked like it had a small explosion go off inside of it Im sure its what killed the resistors, I replaced the actuator with a used one that I took apart, cleaned and tested the actuator works just fine now reads as it should and works as it should, Im now Im just working on trying to get it to be smoother when its working it tires to adjust it self all the time speeds up then it holds for a moment then it will slow down
and hold again for a moment and then it starts all over again over and over again it never actually holds the constant correct speed