Digiplexes --- several on Ebay currently

You don't see these come up available very often, so I thought I would pass this along in case anyone is looking to replace / rebuild their units.

Interesting variety ---- US, Euro, NOS, used, rebuildable...

Ferrari 308 Magneti Marelli Digiplex | eBay

Magneti Marelli Digiplex Ignition Module Med 801 A Ferrari 308 Mondial | eBay

Ferrari Mondial 8 308 Gtbi Gtsi Digiplex Orig 115977 | eBay

Magneti Marelli Digiplex Ignition Module Med 801 A Ferrari 308 Mondial | eBay

Ferrari 308 Euro Digiplex Ignition MED803 118451 New | eBay

Magneti Marelli Digiplex Ignition Module Med 801 A Ferrari 308 Mondial | eBay

 

There is this outfit in Florida that claims to be able to rebuild / repair them --- but, I don't know anything first hand about their capabilities.

Ferrari 308 QV ECU Magneti Marelli Digiplex MED 805 A - Specialized ECU Repair

 

Frank ----

Which model is your unit ? ---- should be an 801 if your car is a US-spec MY'80...

One of those Ebay listings is for an 801 ---- used, but good working order, asking $495. Not cheap, but a helluva lot cheaper than any aftermarket ignition setup currently out there --- not to mention easier to install.

Seller is an F-Chatter, "Colorado Tiger", I believe. He recently did a 3.5L / ignition upgrade, so is getting rid of his stock system ---- seems like a good, stand-up guy from all his posts.

Also, AW has a "new" 801 unit listed for a BIN price of $1,265 / offer......but, at that price point, some of the aftermarket systems probably have to appear in the trade space .

 

I don't know what Brian's experiences have been, but I can share mine.....

Many years ago, I started "collecting" failed units because I had the idea I would play around with them, and see if I could repair them. Alas, that "project" evaporated among the constraints of not enough free time, not enough sustained interest, and too many good alternative solutions becoming available on the aftermarket. So, I ended up with a box of partially dissected as well as intact (but fried) units .

++++++++++++++++++++++++++++++++++++++++++

What I did learn from playing with them was the following, as far as most common failure mechanisms ---

1) Rarely (if ever) does the most important component (the CPU / EPROM [MCU, if you prefer]) fail. And when it does, it typically burns along with several other discrete components and ICs as a result of some power overload ---- either from improper attempts to jump start the car (a big "no no" with these cars), or some improper manipulation of the car's electrical system that spikes / shunts power to the ECU harness (particularly vulnerable if the ECU ground loop is compromised --- which happens often). Obviously, when these ICs are fried, it is catastrophic and cannot be repaired (unless you have the ability to spec, and source, all the components and burn a new EPROM with M-M's data / code ).

2) The APS sensor (if you can call it that as it is more of a generic pressure transducer) is a very crude design LVDT-type device actuated by intake manifold vacuum. Internally it has a conductive rod / plunger (moving within 2 coil windings) attached to a rubber diaphragm that reacts to changes in vacuum pressure. The diaphragm often ruptures --- it is un-repairable and un-replaceable. If a healthy one were properly characterized mechanically and electrically, an alternative device could likely be found and substituted, I suppose, if one were so inclined and properly motivated to go to the effort.

3) However, of all the dozen or so units I took apart, by far the most prevalent failures were within the structure of the PCB. These PCBs are poorly constructed and are mounted / sealed in such a way within the case that they are subjected to excessive heat and significant moisture. As a result, from corrosion and repeated thermal cycling, the connections (traces) themselves fail (open circuit). This is a simple failure to isolate and the connections can be easily repaired ordinarily, however and unfortunately, removing the boards or attempting to expose them in order to locate the failures (and have access to repair them) is extremely difficult to accomplish without doing a lot of collateral damage to the PCB --- they are simply too delicate and it takes too much "aggression" to remove the potting material. The result is that you typically destroy (effectively) the board while you are trying to access / repair it ---- rendering it into shards of hopeless.

++++++++++++++++++++++++++++++++++++

Based on my experience, and IMHO, the best way to "repair" a bad board would be to actually build a new one from scratch, and to pull off and re-use the key ICs and main CPU from the old one. For someone who has a good knowledge of PCB design and construction, this would not be too difficult ---- as the board circuitry is reasonably simple (and only single layer).

FWIW

 

Actually, MM used the old-school RCA 1800-series, gold / ceramic, 40-pin, processor for these applications. Although you can still find these things available (NOS) laying around in vintage electronics inventories, if someone were to do a rebuild, it would certainly be a good idea to replace it with a better, more modern, processor .

You would not even have to go through the effort to decode and extract the data from the original CPU or even fully characterize how it is operating. Something very "handy" for someone looking to create one from scratch is that Ferrari supplied charts (in the 308 / Mondial workshop manuals) that have all the ignition curve data (degrees vs. rpm vs. vacuum load) for all the various iterations --- 801, 802, 803 & 805 MED units --- and, they are simple, perfectly linear curves, divided into just a few discrete on / off / next segments (a no-brainer for programming) .

Precisely --- that is the scheme. IIRC (and don't trust my memory too much..... I'm getting old ), the LVDT is not instrumented directly as it would be in a proper test application --- whereby it would supply an output voltage. Instead, low current (again IIRC, it is rectified to DC prior to input) is passed through the coils and it (output current) is increased / decreased as the magnetic plunger position changes and varies the equivalent inductance of the coils. The output current then feeds into a Current-Controlled Voltage Source OP Amp (off-the-shelf item) which generates a variable voltage signal to the CPU --- this gives the CPU operating points for engine "load" to select the appropriate advance curves from the function generator element.

Correct --- the earlier units ('80 to early '81') had the PCBs potted in a white silicone, but from then on, for some reason, they switched to a black silicone. The white is easier to remove, btw .

 

Peter ---

Actually, that unit is fully sealed / potted ---- in the "white" silicone. The PCB is entirely hidden, but some of the tops of the surface mount components protrude partially through the coating The CPU (that is the earlier version 801) just happens to have a white-colored package casing, by coincidence.

 

Oops....my mistake....thinking of something else! Told you my memory is fading It IS the 89711 chip, 24-pin.

Correct ---- there are a couple more discrete amps on the board

For reference on the CPUs used, I dug up these old close-up pics I took ---- first one is the earlier version CPU (and entire unit), second one is the later version. In both, you can more clearly see the potting scheme --- white vs. black.
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