Repairing a Marelli Microplex | FerrariChat
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Repairing a Marelli Microplex

Discussion in 'Technical Q&A' started by alhbln, Oct 28, 2015.

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  1. alhbln

    alhbln Formula 3
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    #1 alhbln, Oct 28, 2015
    Last edited by a moderator: Sep 7, 2017
    I've started this thread to discuss how to repair and rebuild Magneti Marelli Microplex ignition controllers. Microplex units were used in the Ferrari Testarossa and Ferrari 412 (Microplex MED120B), in the Ferrari 328 and Mondial 3.2 (Microplex MED806B) as well as in the GTB Turbo (MED807B). They are not potted and use standard through-hole components, so a repair is relatively straightforward. To make the diagnose a bit easier, i've created a set of documents with detailed information about the Microplex.

    Only two of the electronic parts are NLA (the Motorola 6805 controller and the custom build vacuum sensor), my plan is to design a modern embedded replacement board for the Motorola chip as well as a vacuum sensor replacement based on modern components.

    I'll also try to give easy step by step guides how to test for common defects (bank failure, vacuum sensor problems) in future posts. If you have access to a scope, you might want to start with the "circuit board test points" document as below for a first diagnosis.

    I'll begin with the Microplex MED120B circuit board diagram with component list, circuit board test points, connector pinout and vacuum sensor voltage map, which are available here:

    Magneti Marelli Microplex Support Documents

    The circuit board is quite detailed, so the recommended way to use it is to open it on a computer and zoom into specific areas you might be interested in.

    Also a big thanks to Steve Magnusson for his excellent support.

    Enjoy,
    Adrian
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  2. Badman

    Badman Formula 3

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    #2 Badman, Oct 29, 2015
    Interesting project. I know that Ferrari Service of Bedford, who make new Digiplex boards (I've got a set in my car), are very soon releasing new Microplex boards using a completely modern design, with a 32 bit arm processor and a modern vacuum transducer. Might want to get in touch with them instead of reinventing the wheel.
     
  3. alhbln

    alhbln Formula 3
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    #3 alhbln, Oct 29, 2015
    My scope is to preserve the existing instead of replacing it, so it's not really reinventing the wheel for me. The Microplex design is robust and quite clean, and it does the job. A repair is quite feasible and most defects would only require to exchange one or two cheap components to fix it, so i think it's worth the effort.
     
  4. Wade

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    #4 Wade, Oct 29, 2015
    Last edited by a moderator: Sep 7, 2017
    So glad that we don't have to deal with this!
    .
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  5. Badman

    Badman Formula 3

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    #5 Badman, Oct 29, 2015
    I suppose, although this pcboards are getting on 30 years old, a lot of the ones I've seen have pretty poor traces on them. Personally, if my box died, I'd want a fix that not only used modern power protection and noise suppression, but that would work for another 30 years without something else failing.

    I suppose there's room for both approaches to the problem...
     
  6. Wade

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    #6 Wade, Oct 29, 2015
    Enjoyment and self-satisfaction for a few dollars on one hand vs. modern plug & play for $$$$ on the other. But yes, both solutions are needed.
     
  7. theunissenguido

    theunissenguido F1 Rookie
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    #7 theunissenguido, Oct 30, 2015
    Thanks for putting so much efforts in those projects....seems to me you did calculate wrong in the beginning...way to cheap for doing all this.
    What about the Med 803A for mondial 3.0 QV ?

    Guido
     
  8. alhbln

    alhbln Formula 3
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    #8 alhbln, Oct 30, 2015
    Last edited by a moderator: Sep 7, 2017
    The MED803A is a Digiplex, which is difficult to repair due to the circuit board being a hybrid design.

    I designed a new automotive grade replacement board (picture for people who like to look at circuit boards below :) for the Digiplex some years ago, but stopped working on it when Ferrari Bedford announced their remanufacturing offer, as the problem seemed to be solved by that.
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  9. andyww

    andyww F1 Rookie

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    #9 andyww, Oct 30, 2015
    Looking at the Microplex parts list there are 4 electrolytic capacitors on there. They would likely be the first components to go out. If any problems it would be worth changing those 4 as a matter of course.
     
  10. alhbln

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    #10 alhbln, Nov 13, 2015
    Updated the following Microplex MED120B PDF Documents:
    - Circuit Board Diagram / Component List
    - Circuit Board Test Points
    - Connector Diagram

    Magneti Marelli Dinoplex Repair and Restoration Documents

    If i have some spare time i'll clean up and finish the MED806A documents next, and then post a bit of text about common defects and repairs.
     
  11. TacElf

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    #11 TacElf, Nov 18, 2015
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    Ferrari Service of Bedford is making progress on their replacement Microplex boxes. The first-revision PCB boards are done and they have a full bench setup of a Ferrari 328 ignition system to hook it up to. They also have the Microplex (US spec) box out of my 328 in which to compare against.

    Beta testing will commence once they are satisfied everything is in order.

    To whet everyone's appetite, here's the waveform produced by the new boards.
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  12. synchro

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    #12 synchro, Nov 18, 2015
    What is the common mode of failure when these go bad?

     
  13. alhbln

    alhbln Formula 3
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    #13 alhbln, Nov 18, 2015
    Jeff, with all due respect, this is a thread about repairing and documenting the original Microplex. If this is not of interest i am fine with stopping to post updates.

    Scott, i'll post most common failures and diagnostics in the next days (if of interest).
     
  14. synchro

    synchro F1 Veteran

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    #14 synchro, Nov 18, 2015
    Thank you,
    Always impressed at the level of detail in your threads, this is like a novel and I'm jumping to the last page, apologies
    Excellent background on the need
    Scott
     
  15. SeattleM5

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    #15 SeattleM5, Nov 18, 2015
    Adrian, I am most interested, as I'm sure many others are as well. Please proceed!

    Thanks again for going to the trouble of sharing this with the community, it is much appreciated.
     
  16. Wade

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    #16 Wade, Nov 19, 2015
    +1
     
  17. alhbln

    alhbln Formula 3
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    #17 alhbln, Nov 25, 2015
    No problem, i'll finish the documents on the 806 and then start with the repair documentation.
     
  18. chinook

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    #18 chinook, Nov 25, 2015
    + 1 Thanks for your time and efforts, Adrian.
    Regards from spain
    Eulogio
     
  19. DGS

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    #19 DGS, Nov 25, 2015
    +1 on both.

    While I'm interested in documentation of the original, I'm also interested in the Bedford replacement, if it's really "plug-in" compatible.

    I once looked at building a plug-in replacement ignition, using the stock flywheel sensors, but I got carried away, and started looking at a coil-on-plug solution.
    ... And then realized that no shop would be able to deal with a custom ignition.

    So, yes, both approaches have value.
    Perhaps the replacement could be a separate thread.
     
  20. Stefan Elshout

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    #20 Stefan Elshout, Dec 15, 2015
    Fantastic, i'll follow these threads with great interest! Really valuable to me at least.
     
  21. Stefan Elshout

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    #21 Stefan Elshout, Dec 16, 2015
    Do you know if there are any programmes available for diagnosing these microplex ecu's? These unit's are also used on Thema 8.32 and it has a 3-pin superseal diagnostic socket and can be 'diagnosed' with a fiat/lancia tester (most likely the same thing as a Ferrari tester). I just did something similar on a delta evo with a IAW system, and that system also uses a 68 series microcontroller. With the correct program, an OBD to Fiat-3pin and a ISO-KKl interface you should be able to monitor the parameters realtime.
    For these delta's someone wrote a simple DOS based program which showed all necessary parameters.... would be fantastic to have something like that for diagnosing these ignition systems.
     
  22. Mark 328

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    #22 Mark 328, Dec 17, 2015
    Adrian,
    Great post; its so great that you take the time to do this. I am a tinkerer and would prefer, if I had a failure, to work thru your documents/tests.
    I can't wait to see your 8 Cyl documents.

    Thanks,
    Mark
     
  23. alhbln

    alhbln Formula 3
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    #23 alhbln, Dec 18, 2015
    Reverse engineering the serial protocol is on the roadmap, the protocol supports engine rpm, current advance, advance curve selection and current manifold vacuum.
    Keep in mind that this is seems to be only supported on the MED120B/D, i haven't been able to coax the MED806A or MED120B into activating the debug output yet.

    I'm a bit behind schedule but hope to finalize and post the MED806A documentation between xmas and new year.
     
  24. Stefan Elshout

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    #24 Stefan Elshout, Dec 20, 2015
    That would be really helpful!
    I have a list here with some 50 different microplex ecu's (only Fiat/Lancia) and the required 'tester module' needed for each one of them. They show 2 different modules in total to diagnose all microplexes so they might have changed the protocol somewhere along the way. I also notice that these 2 modules are the same ones used to 'diagnose' almost all available digiplex units.
    Can't really see any logical clarification yet for the A/B/C/D/E/M units, do you have any idea if and what they would mean?
     
  25. alhbln

    alhbln Formula 3
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    #25 alhbln, Dec 20, 2015
    There might be even more protocol versions as Microplex units have a slightly different circuit board for each application/sensors and sometimes even a different (Motorola) CPU than the MC68705R3 used in the 120/806/807 series, but i don't think that there is that much difference between them.
    I need to get hold of a MED120B/D to start reverse engineering the protocol, the MED circuit design supports a tester since the 806A but the embedded software apparently does not except for the 120B/D.

    MED (Type) (Version) / (Option)

    MED120B/D is for version B of Type 120 with the Option /D for the serial tester.
     
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