Table of Contents


This part was taken from a Motronic M1.7.3 engine control unit (ECU), which was commonly used on 1.6L & 1.8L 4-cylinder BMWs of the mid-E36 generation. While this chip was likely used on a number of ECUs, the specific one in this case had Bosch PN 0 261 203 661.

This chip is believed to be a National Semiconductor LM2903 dual differential comparator. Functionally, it is used to detect fault conditions with the ignition coils. When the primary current to an ignition coil (basically, a high-ratio transformer) is switched off, a voltage spike is produced which the switching transistors clamp to ~325V. This spike is divided by resistors and fed to this comparator. If the spike is more than ~200V (in this implementation) it will cause the output of the comparator to latch high, until the ECU's MCU reads the signal and issues a reset pulse via the other comparator circuit.


Label (top):

[National Semiconductor Logo] 59BB
B57678 (Bosch internal PN)


Decap Steps:
(Bic lighter + water quench) x 2 cycles
Selective crushing with pliers and bench vise

Capture Details:
Imaging device: Keyence VHX-2000
Magnification: 1000X


Imaged using normal / center lighting:

Imaged using edge lighting, for enhanced shadow contrast:

Note: The metal layer got a little smudged in some places during mechanical decapsulation.

felinefriendly/bosch/b57678.txt · Last modified: 2018/07/27 22:40 by e30tuner
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