Cruise Control Brain

[Otto]

Otto's has these in stock at $150.00 for a rebuilt exchange unit plus shipping.
The warranty is three years.

[Wavey]

Uhh.... rebuilt by Loren, correct?

[cgarr]

Rebuilt or repaired?

[Tim Polzin]

I've studied the board a bit more. Looking at the component side of the board with the connector to the right, the mosfet and capacitor in the lower left corner appears to be part of the sample/hold circuit. The cap is a high quality metalized polypropylene film capacitor 0.1ufd used in conjunction with a very high resistance input on the mosfet. I'm still not sure of the function of the coil immediately above the mosfet/cap, perhaps to filter the input.

The black rectangular box center right is a relay. The two chips are simple quad comparators.

The board appears to have been dipped in shellac. Nail polish remover seems to lift it nicely, but tends to remove some of the printed numbers on the parts.

I'm going to try building a test bed to bench run the board this weekend. If I can fake the board into thinking it is working, I'll be able to learn a lot more about how it functions.

Perhaps more information next week. I'll post what I learn.

Tim

[Rot 911]

Tim your tests are really going to help a lot of us that would like to keep their CC working.

[rusnak]

I've been reading up on this a little bit at a time. I came across this site
http://www.pca.org/tech/tech_qa.asp

and this came up:
"I don't have a Bentley manual, so don't know what they left out. Here is a quick check of values at the plug to the control unit while plug is disconnected:
1. 11-17 ohms between 3 and 7. If not, check relay for continuity between 30 and 87a. If OK, servo is bad.
2. 12 is ground. Also, relay should activate when clutch is pushed. 12 is the ground side of the relay activation circuit.
3. Ohms between 11 and ground. Roll car. meter should deflect periodically. If the speedo doesn't work, no cruise
4. Open circuit between 6 and ground.
5. Turn key on. With brake pedal depressed, should have 12 volts between 6 and ground. If not, check brake switches.
6. 12 volts at 8 with switch lever up.
7. 12 volts at 5 with key on. If not, check fuse.
8. Ohms between 8 and 5. Normally closde, goes to open when switch pulled to off.
9. Ohms between 9 and 5. Normally open, goes to closed when switch pulled to set.
10. Ohms between 10 and 5. Normally open, goes to closed when switch pulled to reset. Failure of steps 8,9, or 10 indicates a bad switch. Failure of all three may also mean switch wiring disconnected. Print this out, write down what you get. Let me know if you have not found the problem. Good luck!

Chris Powell - PCA WebSite - 12/29/2005"

apparently our 911s (1984-89) use a 928 cruise control module. People looking into this might have some success using "928" under their search terms.

[Tim Polzin]

I started a new thread with current information

http://forums.pelicanparts.com/porsche-911-technical-forum/394659-understanding-vdo-cruise-control-amp-post3789513.html?posted=1#post3789513

Tim

[dshepp806]

Originally Posted by Tim Polzin

I started a new thread with current information

http://forums.pelicanparts.com/porsche-911-technical-forum/394659-understanding-vdo-cruise-control-amp-post3789513.html?posted=1#post3789513

Tim

FINALLY: some schematics and one helluva discussion!!

Many thanks!!