PeachParts Mercedes-Benz Forum - 10-Pin Vacuum Type Cruise Control Analysis

Hey everyone,

Part Number: 001 545 21 32. 1978.

Component Side:
http://i.imgur.com/kKyftl.jpg

Rear:
http://i.imgur.com/2SnXKl.jpg

Someone was kind enough to send in a vacuum 10-pin cruise unit for some attempted repair work. The gent that sent this unit in reported that it did not work at all.

I figured this would be a good opportunity to do some analysis and post up some results.

I'm not all that familiar with these types of units, I've done some minor background reading, nothing too in depth. But from what I gather the output signal to the vacuum actuator is a PWM (pulse width modulation) signal.

Pinout of 10-pin cruise:
http://i.imgur.com/COx8Xl.jpg

Here are some shots from my oscilloscope:

Yellow = Function Generator (Speed)
Blue = Observed from Cruise.

In this picture, I have the unit:
-unpowered
-observing pin 3 with respect to ground.

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

When I varied the speed, this output matched the change.

In this picture, I have the unit:
-unpowered
-observing pin 7 with respect to ground.

http://i.imgur.com/CCt2K.jpg

This output did nothing while the unit was without power.

Turning power on we get the same output from pin 3 (not pictured ) and nothing from pin 7 (not pictured). But when we send 12V to pin 5, we get life from pin 7. Pin 5 is the "accel set" function.

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

So it seems somthing is happening. That something only happens when the unit is commanded to accelerate. My experience with the newer design suggests that once commanded it should perform on its own.

Also the output does not look very clean. Hopefully fresh capacitors will resolve some of the issues. This unit appears to use two 47uF / 16 V rated capacitors.