Problem: CCM kept throwing up ESD Regelt error for no apparent reason
Solution: bad resistor; FIXED
For those who have cracked the cases on the CCM, you'll no doubt recognize a highly symetrical design.
This is for a reason... there are about 30 separate, but identical test circuits in the CCM that check everything from your brake lights to the key in the ignition.
Every single one of these test circuits is set up as what is known in the business as a "current loop".
That means that the system sends a current through the closed loop of the and measures the voltage drop across a precision resistor.
If the drop is out of range, you get an error. Not to difficult.
Anyway, to debug my CCM, I took the cases off and put it back in the car and started the engine. Immediately I got the ESD Regelt error.
Using my multi-meter, I started testing the voltage at the precision resistors. All were the same... except for 1.
Hmm. I pulled the CCM and put it on the bench.
Again using the multi-meter, this time in ohms mode, I measured the precision resistors.
Each bank of precision resistors has 4 2K ohm resistors and 1 1K ohm resistor... again, nice symmetry.
Problem was, one of my 2K ohm resistors was 2.7K ohms... since I did not have any spare precision resistor networks laying around,
I instead calculated that an 8.2K ohm resistor in parallel with the suspicious 2.7K ohm resistor would bring the value back down to the required 2.0K ohms.
30 seconds of soldering and the new resistor was in place. I left the case off the CCM and plugged it back into the car.
ADDENDUM -- added Nov' 6, 2009
There is some dispute over this statement Ð judging from the circuit diagram below there are several different resistor packs
with different numbers of resistors. Rick 540 found a failed resistor pack with originally NINE 1 kilo-ohm resistors -
he replaced the pack with a set of EIGHT 1 kilo-ohm 1% resistors as
shown below.
Hey, no more ESD-Regelt!
I checked the voltages and all were exactly the same - as they should be.
Anyway, thought I would post this since this is one of those gremlins that could be hard to track and cure... it's sort of analogous to the capacitor fix for the cluster.
Of course, this problem could have been solved by purchasing a new or refurbished CCM... but then again, we're all trying to keep that cost of ownership down!
This info was posted by Kevin on RF March 30, 2002 -- photos below are from the Japanese BMW group - many thanks guys
location of CCM
remove the back panel
Serial number for this unit
Board mounting view -- appears to be glued to the back plastic plate.
Squeeze the bayonet pins to release the board
top view of the board -- the poster replaced the capacitors but this
did not
eliminate the weird CCM warnings. Get your digitial voltmeters out and
start checking the resistors.
NOTE: different CCM models will likely have different parts arrangment!
But diagnosis is same.
Problem: CCM kept throwing up Brake light error for no apparent reason
Solution: cracked solder joint: FIXED
This is a translation from the Japanese report written by JB1, an Alpina freak of the best kind.
This is the schematic he used
His analysis was that the Brake light warning was thrown because P2 on IC2
was NOT HIGH.
This was due to some problem with the resistor group R60.
R60 checked out ok, so he figured that the common supply was at fault.
topview showing R60 and the common supply
bottom view showing common supply pin
fixing the solder joint
Voila, pin P2 on IC2 is now high and the problem has disappeared.