Just found out today that my Microplex MED806A has partially failed - the vacuum advance side is not doing anything. Fortunately for now the electronic timing control part still works, but I'm afraid the whole thing will die. I fully realize these are unobtanium - and the last 'dealer price' was around $3300 USD !! I did a search and couldn't find any results - but grasping straws here. Does anyone know if there is a rebuild place anywhere? Seems to me it's just a box with parts inside. I've been an electronics geek for decades - we all call it a computer, but I highly doubt there is a true CPU - probably a bunch of discrete components - surely should be repairable... For now my F-wrench has tweaked me to a compromise safe running setup, but obviously without advance my 328 is not going to be at its prime Any suggestions or help on this dilemma would be greatly appreciated. I'm concerned the rest of it will die and leave me stranded with a tow truck en route... Original Ferrari part 187422 according to an old post I found in the archives. Thanks Jedi ps - yeah, this item too was not listed on my PPI - just add it to the list of crap I've been sorting out since March.
How did you determine the vacuum advance portion is not working? If it has failed it is no doubt the vacuum module itself (electro-mechanical) which I would not associate with the expected lifespan of the electronics. In other words if the vacuum module no longer works (moves) I would not assume the electronics are on their way out also. However, I think it would be safe to assume the car will not be running anywhere near as well as it should if you're only running on a default ignition map instead of all nine.
The vacuum sensor transducer is mounted inside the Microplex case. So that just shifts the question to finding a vacuum transducer of unknown make, model, or specification, and then dissecting the Microplex to swap it out. There was a thread, a while back (either here or in the 3x8 section) where someone opened up his Microplex to try to identify the vacuum sensor, only to find that the vac sensor in his computer was missing completely. Most people, these days, find it easier to convert to an aftermarket system like Electromotive. There are also a thread on conversion to individual plug mounted stick coils. (COP or "coil on plug") But the aftermarket systems tend to require mounting their own flywheel sensors, rather than using the ones already built into the 328.
I just removed my Microplex from my 88 Mondial as it was replaced with a different ignition system. If interested, drop a PM. Good luck! rt
One other option (although I'd guess that the shipping/customs+turn-around-for-repair+shipping/customs might be fairly lengthy) is this firm in the UK (and getting Russ's used unit would be a good find -- IME the failure rate is higher than the crash-out rate so not easy to find a used MicroPlex): http://www.the-ecu-doctor.co.uk They actually show a MicroPlex from a 328 as a past patient (although maybe that was for some other fault). Has anyone used them lately? I've got an injection ECU that I'd like to send to them (this was easier to find used so turn-around time not a big issue in this case being a spare), but I'm not too keen on sending my stuff to an address from a website without some prior contact, and they haven't answered my email yet -- anyone know them, or can confirm that they exist at that address?
My F-wrench happens to have another 328 in for a Major, so while I was there yesterday he swapped Microplex units - that's how he confirmed that mine is not functioning. Yes, it's not running fully up to par. He has tweaked it for a 'good compromise' timing that runs smooth but obviously is NOT at peak performance. It's not bad - just not great at higher revs. And now that I think about it, my assumption of failure of electronics is in fact not connected to a failed vacuum transducer, which is largely mechanical. Given the green-brown mud found in the trunk bay (hidden under new carpet, missed in 2 successive PPIs in the last year), it's highly likely that the mud / water got in the transducer. I may try taking it apart for a good cleaning and see if that has any effect. Can a Microplex safely be opened? I don't have the car here so can't look at it. But is it riveted shut? Welded? Or does it have screws that allow a look inside? Jedi
Wow. It's not potted in epoxy! That unit should be fixable... I'm a long time electronics geek, and will dig into the old one (as a spare) once the new one is in. I don't see anything that looks like where the vacuum line would connect... seems there should be a small black (or whatever!) module that would contain the vacuum sensing transducer itself. Can you shoot another photo (closeup if you can) showing the exact gizmo that the hose feeds into? Anybody by any chance have a schematic for that bad boy? Repairing something like THIS is in my ballpark! Can't do diddly on engines, but electronic stuff? you bet! So now the quest for a schematic... Jedi
If it's something like a 3 terminal voltage regulator (small outline), then that's not such a big deal. If it's a big 40 pin IC of unknown function with bizarre "in house" numbering that is not sourceable (big outline), then trouble looms ahead. If you can't get a copy of the schematic, (which is highly unlikely because Ferrari probably considers that a confidential item), then repair is going to be very difficult. Image Unavailable, Please Login
Agreed on all points. My thought is that the vacuum advance portion of the unit is simply a mechanical sensor - very likely has an optical mechanism, that as the vacuum level changes, so does the light level falling on a photo resistor (much like in a vintage optical compressor module of the same era). I would expect that the mechanical bits and optical bits are in a small housing that theoretically could be opened and cleaned. That (theorized) optical (or other) device simply feeds a continuously varrying resistance to the electronics in the circuit, which then alters the advance appropriately. I don't suspect that my vacuum advance problem in in the electronics - given that mud was found in the trunk I suspect the mechanical bits have been fouled and just don't move anymore. But it's certainly a reasoned guess, and boy wouldn't the F-chat crowd love to know that you COULD fix that part of the unit! And yes, house numbered chips suck. I can draw the schematic if I have to, but if the chips can't be ID'd then there would be no hope of repair. It's a LONG shot. A VERY long shot. But hey - once my new/used box is in place, I can freely experiment with the old one with no loss worries. I'll keep you posted when a new unit turns up and I can start digging into this. Jedi
If one had the patience to flip the circuit board back and forth a thousand times, it is possible to draw out a schematic. (I did it one time on a VCR power supply of similar vintage and board size.) With a schematic suitably drawn out, it would be possible to determine the function of the unknown IC by their position in the schematic diagram. I spent a lot of free time many years ago drawing out some diagrams of possible ways to drive a solenoid fuel injection system WITHOUT having to use a factory module and use my own module of my own design, which of course would be very cheap to build. Mass Airflow Sensors and vacuum sensors feeding voltages to monostable multivibrators and comparators was all part of the fun. Toss in plenty of pulse width modulation and some start enrichment pulse modifiers and then your brain gets tired and time to go eat lunch or watch TV!!!
No, it's not that 360 part shown -- the 328 MicroPlex is further down the page. Amen Horsefly -- big custom ICs "of unknown function" are a real obstacle. The device converting the vacuum signal to an electrical signal is on the top of the PCB (between the PCB and the outer case) in the raised rectangular area so you'd have to remove the PCB to see it. Haven't looked at one myself, but the two things I've learned are: 1. It is physically smaller than what was in the Digiplex, but 2. It still has a troublesome internal diaphram that fails (used, working MicroPlex for TR are hard to find IME). Image Unavailable, Please Login Here's the larger (round) unit inside the DigiPlex: Image Unavailable, Please Login
Marelli pretty much disavows all knowledge of the units. Ferrari wouldn't have had the schematics to begin with, I think. And I'm not so sure about that complex, nine step advance map posted in the Ferrari tech specs, either. As far as I can tell, the flywheel sensor produces 144 pulses per rev. That's only 2.5 degrees of resolution of crankcase angle. With a modern CPU (like a Renasas M32), I could extrapolate between pulses with a 12 bit timer (and a 4K x 12 bit map) and get a close rendition of the published advance curves (8bit x 8bit is somewhat choppy). But how would they do that with 1970's components? That sits in the engine bay? (We couldn't get industrial temp spec CPUs till the '80s.) And the specs I have only show the maps for the US version. With three personality pins on the box, there could be up to eight sets of maps programmed. If someone could run a good one through a curve check, we could probably come up with a plug replacement using modern parts. But designing one and building one that would run for 20 years in a hot box are different things.
Uggghhhh,.....I see potting compound, the bane of repair work. Put there under the pretense of waterproofing, but more likely to thwart efforts at repairing a $3000 ignition module and forcing you to buy another one. Too bad it's not a '66 Corvette transistor ignition system; the schematic is right in the shop manual along with troubleshooting procedures.
This all reinforces why I prefer pre-1980 electronics when REAL men built REAL devices out of REAL integrated circuits and transistors! We didn't need no stinking microprocessors!
Hi Steve, I have a friend who lives in that part of the UK (over 4 hours driving time from me) who is also a Ferrari owner and in the motor trade. So if they are known he should be able to let me know if they are as good as they say they are on the their website, I will get back to you with any comments ASAP! Regards, Phil.
Just came accross this thread and realized I have a used "good when it came off the car" Magneti Marelli MED 801 A digital ignition advance system. I am sure it is from the 308 range so not sure if it is entirely compatible with the 328. I am going to list this on ebay along with a few other ferrari parts but if anyone on here is interested I am looking for $850.00 for the unit. drop me an email, [email protected] and let me know thanks Paul
Different set-up entirely than used a 328 (single unit), but still a very fair price for a used spark box. David
Hi, Fiat Uno Turbo has the same exterior....308 and mondi are using 2 digiplex so each for 4 cylinders. Maybe 1 Fiat digiplex has the same interior used for 4 cylinder also... Anybody has a fiat Uno Turbo digiplex ? Enzo52 Image Unavailable, Please Login
If you'd like your buyer to be able to make a more informed decision, what you have is a Magneti Marelli Digiplex MED 801A as used on 1980-1982 US Version 308i-2V.
