pcb Need help with identifying diodes in a 1970s automotive circuit

Posted on Feb 7, 2014

An old ignition module from a 1978 W116 model Mercedes-Benz, and I`m trying to `reverse engineer` it. The original circuit diagram is not available to mere mortals, so I have made one based on the PCB itself. I believe it is, beside being ugly, electrically correct. Thus far I have identified all resistors, caps and transistors (bar one). What I have a huge problem with are the diodes, and any help would be

pcb Need help with identifying diodes in a 1970s automotive circuit
Click here to download the full size of the above Circuit.

appreciated. ZD4, ZD5, D1 to D8 are unknown. ZD4/ZD5 are not shorted, but I`m getting nowhere with these with my 30V power supply, so they`re probably rated above >30V. D3, D5 and D6 are fried. D4 is just beside R4. The two left-most black diodes are D1 and D8 (both marked "703"), the one underneath them is D7 (marked "1849" and "714"). The missing T5 transistor is a TO3 packaged power transistor marked "1120008" and "7/32". I haven`t cracked this one myself, but have been told a BU426A is a direct replacement for it. T1 to T3 are BCY58IX, T4 is a BSV15-16K.

Leave Comment

characters left:

Related Circuits

  • New Circuits



    Popular Circuits

    very stable BUG
    AC Motor Speed Control circuit
    12Vdc Mobile Battery Charger
    Continuity Checker
    Speech Scrambler Circuit
    motor control
    TENS Circuits
    30 volts panel volt meter using pic mcu
    High voltage direct current
    555 monostable circuit trigger solenoid
    fm radio receivers
    DC bridge amplifier circuit