My blower motor stopped working and the ecc showed the error code: starting current too high. So I started to find out what is wrong. The blower motor looked fine and was easy to turn and worked in position defrost and full power (RL1 closes). So I had a closer look at the power stage. As I am only good in mechanics, I draw the layout/circuit diagram of the circuit board to talk to a friend who is good in electronics. The board has a printing:
ALPS MA97H08
We found out that the capacitor C1 (big black one) leaked some acid and damaged the isolation of two conducting paths which leads to a short circuit so that the transistor TR1 pulled the basevoltage of TR2 down to ground before this one could begin to open. I cleaned the board under the capacitor C1 and replaced it. Now the blower motor works fine again.
Some more words about what I have understood so far:
The two operational amplifiers are for controlling the transistor TR1 which pulls the basevoltage of TR2 down to ground to shut down the blower in case of too high current of the blower motor. The op-amp of pins 1-3 sets the base level of the allowed current which is dependent on the wanted speed. The op-amp of pins 5-7 compares the allowed current-level with the used current and decides to let TR2 work or shut it down if the current is too high.
Some data for the communication of the ecc with the power stage without engine running:
Blower control: <-> Voltage on CN2/4:
0 <-> 0 V
1 <-> 1,5 V
2 <-> 1,68 V
3 <-> 2,04 V
4 <-> 3,82 V
5 <-> 5,57 V
I do not know in which other Models this power stage is mounted too. Therefore I attached a photo of the power stage. On the photo C1 is soldered out. As it took me several days to understand what the circuit board is about and for measuring, I would like to hand out my circuit diagram in this forum which has helped me many times. I hope somebody can use it and save its power stage.
Björn