Repairing a Marelli Microplex

I should have finished the MED806A documents by now but got a bit distracted and build myself a small Microplex tester to help with testing a full car setup.

The tester is meant to be plugged in-between the Microplex and the car wiring (connector for diag cable on the top right), and has another socket (bottom right) for a cable to the round test plug in the engine compartment. On the left side is a DB9 serial connector for connecting a Laptop or PC to access serial debug information and runtime data (e.g. replacing a Ferrari Tester).

Some of the features:

- TDC and RPM sensor coil/wire test and signal output display
- Leds for ignition trigger and spark discharge to diagnose ignition module and coil defects
- TDC/RPM Sync Led to indicate if TDC/RPM ratio is correct (green) or if the sensor is faulty (yellow=too few RPM pulses / red too many RPM pulses per TDC segment)
- Manifold sensor vacuum level display via Led brightness
- Leds for throttle and cold start injector activity
- Map selection (car type selection, EU/US/Swiss maps etc.) is displayed via Leds and can be manually overridden for testing

That was fun! Now back to finish the documents...
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It looks more similar to the MED807 (mostly due to the advance bit resistors going to the cointer) but the architecture is similar to the MED120/MED807, e.g. you should be able to use the test points from the MED120 documentation. Could you mail me a high res image of the PCB to the mail address on my website?

What is the unit on the second photo with the NEC controller for?

 

Unfortunately the Motorola embedded CPU used in the Microplex is a special version with additional input/output ports, so the CMOS 6809 would not be a direct replacement. And then you would still need the embedded software for the replacement

 

The one in question is a MC68705R3, but there were two different versions with different pinouts. And even if you get hold of one, you would still need the firmware image (the program code) from Marelli to flash it to the MC68705R3.

 

But thanks for looking!