The Dinoplex in my L-series is dead, no humming of the transformer so it was time to pull it out of the car and do something about it. I'd previously cleaned it up, taken it apart/put back together but not bench tested it in the hope it was functional... it was not and we've been running in the "Emergenza" mode. The L-series Dino had a very re-buildable Dinoplex unlike the later cars with all potted internal components and following Adrians excellent advice on dinoplex.org, I was encouraged to try and fix it since it's a good strong system providing excellent spark. I started this thread with the hope other folks rebuilding these might benefit from seeing where all the internals are and a few potential issues/pitfalls. I may even get a few tips along the way to help me out. I had previously renovated the original coil, the 4 pole BZR-205A was leaking so this was repaired, repainted and refilled with dielectric oil. Image Unavailable, Please Login Image Unavailable, Please Login
The coil was running fine in emergenza mode so I'm concentrating on pulling the Dinoplex apart. I plan to buy a decent LCR meter since most of the diagnosis Adrian recommends below is out of range of my cheap, regular DMM. Since I have everything apart and de-soldering components, it's worth checking each one is still serviceable. Magneti Marelli Dinoplex C AEC 101/AEC102 Diagnose and Repair Firstly taking apart, there is a compressed fibre gasket about 1.5mm thick. I probably need a new one since it's soaked in a varnish (presumably to waterproof it) which is disintegrating. Has anyone made these? Image Unavailable, Please Login Image Unavailable, Please Login
Transformer with resistor board on the side. I'm hoping this is in good condition, we'll know once we replace some components and measure the current to the unit. The varnish insulation on the transformer windings breaks down causing shorts, the current goes up and it fails to operate as a transformer. Adrian put a guide as to how much current it should draw depending on condition. Image Unavailable, Please Login Image Unavailable, Please Login
Main board: There is a 160uF capacitor under here which is circled in red that has a high probability of failure so I'm just going to replace it. The new one I have is a slightly larger electrolytic, I bought some 5min epoxy to fix it to the board after scraping off as much of the old epoxy as I could. Curiously, the leads into the board were also epoxy'd down, I guess it was 1960's stress relief of the lead. Image Unavailable, Please Login Image Unavailable, Please Login
Transistor board: There is a plate on the back under which are the 2 power transistors that need to be replaced. After doing power checks, no humming and all dead so these need to come out. These transistors are mounted on a thin ceramic heat sink with a blue plastic mounting pad on the other side. There are 2 machine screws and 2 soldered leads holding this in. You need to be very careful getting the old transistors out not to break the ceramic heat sink. I think the best way to do this without fully disassembling the plastic mount is to de-solder the leads and then cut the 2 leads off each transistor and carefully pull straight out. Image Unavailable, Please Login Image Unavailable, Please Login
Hopefully, these are the only broken components, I will also clean and re-solder all the connections. A new LCR meter is on the way so this weekend I'll check some other components are in spec then try to fire it up.
This reminds me of my radio amateur career some 40 years ago re-building old VHF equipment. Good luck with the cool project Andrew! Best Peter
Thanks! New LCR meter arrived and all the components and the transformer inductances checked out ok when measured at 1kHz. The new transistors went in with some thermal grease (there was none before, was just screwed straight to the ceramic heat sink). I connected everything up again including a well grounded spark plug, switched over to "Normale" mode and applied some power with the case off and it hummed away quite loudly, good news! I think the only issue was the blown power transistors. Next, I measured the supply current and it was under 2A in the idle state. According to the guide on Dinoplex.org, this unit is lightly used and still in good condition so no transformer rebuild required. Nearly ready to re-install... Image Unavailable, Please Login Image Unavailable, Please Login
Andrew, Congratulations on the repair of both the Dinoplex and its rather rare coil. If I could suggest a safety feature, I would recommend putting a 1Mohm to 5 Mohm resistor in parallel with the main discharge capacitor to ensure it always de-energises when the unit is off. Use a carbon composition(edit, not carbon film) of 1 watt or a couple of 1/2 watt 300V rated resistors in series. Some cheaper resistors won't take the high voltage pulses over time. The resistor will also help save the SCR from over voltage spikes and also prolong the life of the capacitor especially if you have changed it over to a more modern polypropylene film type that can hold a charge for well over a month. Well done! Fred
Andrew, my suggestion might not be required. Look at the circuit diagram on Adrian's site. R10 is 470kohm and as long as the coil is in the circuit, it provides the protection I mentioned. Fred
Fred, Thanks for raising this issue and putting some thought into the solution. I checked and there is a large 470kohm resistor on the main board underneath to discharge the capacitor, so I ran a test. Firstly, I measured 527V on terminal C in Adrian's schematic and the RC time constant is about a second. After switching the unit off, it took 7 seconds to fully discharge the capacitor, I also checked with the DMM disconnected as I'm not sure what the input impedance of that is. Got the same answer. It seems only someone powering it with the lid off would run the risk of a shock! Regards, Andrew
Nice work, good photos, Andrew. From your description It sounded like it was just the power transistors, but good that you were able to verify that the transformer was OK too. Adrian has done us all a favor by sharing the detailed reference measurements of currents and inductances with us. The AEC 101 seem so eminently rebuildable. They can probably be kept functioning forever in essentially stock configuration. With the potted AEC 103 boxes we dont have that option. Your restored ignition coil looks very good too. Did you find someone who works on these coils or did you attempt it yourself? Repairing and refilling 40 kV ignition coils is not a completely trivial matter, I imagine. Regards, Lars
Hi Lars, Yes, Adrian has done all the heavy lifting and I just follow the instructions... I liked the fact the Dinoplex system on early cars is rebuildable and reasonably robust. The only other modification is using zener diodes or something to protect voltage spikes killing the power transistors in case of jump starting or battery disconnect whilst running. This was identified as the only issue I'm aware of, need to think about it some more. I cleaned up the coil, fixed the leak. I didn't need to take the whole unit apart. There is a filler screw inside the top HT terminal, just unscrewed it and a few days of suspending upside down to get the oil out with alot of shaking. A note here on PCBs: http://www.ferrarichat.com/forum/206-246/456563-leaking-ignition-coil.html It was repainted by my body shop in Polane which resists most oils etc. Getting the new dielectric oil back in was fun - the filling hole is small so I used a syringe and forced the oil in, compressing the air inside and letting it bleed out. Next time, I'd find a proper syringe with a thick needle. Regards, Andrew
A small correction for Adrian, I noticed on V1.6 of the circuit diagram, C2 is 150uF and not 150nF. thanks, Andrew
Andrew, I'm curious as to why the transistors end up failing with that design. I wonder if it is heat or degradation from voltage spikes, or a combination of both? I'm surprised they didn't use a smaller transformer core and a much higher frequency power supply. I suppose that it lasted as long as it did is quite acceptable compared to modern throw away electronics. Fred
Fred, The owners manual states that the Dinoplex will be damaged if the battery is disconnected while the car is running. The alternator would spike the voltage since the load disappeared, probably similar issues when jump starting, there is no over-voltage protection I can find in the Dinoplex and the ~100V rating on the power transistors could easily be overcome. I'm looking into adding a TVS diode to the car or Dinoplex but I'm not sure where to put it yet so it's most effective. Thanks, Andrew
Fred, I agree with Andrew that voltage transients rather than heat is what caused the failures of the Dinoplexes. This has also been confirmed in previous discussions in this forum. Adrian, who has repaired a number of Dinoplexes reported that often the capacitor across the input was shorted and fried as a result of such transients. In the mid 1960´s designers knew very well how to calculate heat dissipation, but transient absorption was less understood and the components we now have available for that purpose were simply not available. Andrew, I would put a transient absorber from B+ 12 V input to ground right where it enters the Dinoplex box. If it were my unit, I would also replace capacitor C2 with a modern type with at least double or triple the voltage rating. Electrolytic capacitors in vintage equipment are notoriously prone to failure and should always be replaced as a precaution, in my opinion. They are also very poor at absorbing voltage transients (modern ones much better but still not ideal), so I would also put a 0.1 to 0.47 uF switching type capacitor (polypropylene or similar) in parallel with it, to absorb very fast transients. Lars
Andrew and Lars, Thanks for the information. I had assumed a slow death of the transistors from heat, but a slow death from voltage spikes can also occur as can fatally quick ones. Does anyone here know how high the voltage spikes can be with the battery disconnected while the engine is running on the Dino? I am aware that modern alternator diodes are actually zener diodes and clamp the voltage to 30V or so if left unregulated, and that some voltage regulators absolutely require the battery to be connected for them to function. Thanks, Fred
Well, I can try... Yes, alternators are much more foolproof now, and they limit themselves to safe voltage levels even without a load. But that is under steady-state conditions. That is not the problem here. Instead, the damage is done by the very short high voltage spikes generated when you interrupt a high current through an inductive load - without providing a discharge path. This could happen for example when you disconnect the battery while the alternator is charging it. Something very similar could happen when you disconnect the starting battery during a jump start. The violent voltage spike created by the magnetic field in the alternator coils will fly right through the forward biased diodes out on the 12V feed. I do not believe that the Dino alternator is equipped with zener diodes - or anything else to stop such voltage spikes. I could be wrong of course, but it just seems unlikely. (Any alternator rebuilder out there who could verify?) But even if you never disconnect the battery and never jump start the car, you will always have some of those high voltage spikes in the system. They are just part of life in automotive electrics, particularly in vintage cars. In the Dino, for example, spikes are generated each time you release the starter solenoid with the ignition key (no discharge path, no freewheeling diode!). So the best way to deal with this problem is to make sure that anything connected to the 12V system can handle the voltage spikes. And that includes the Dinoplex. Lars
Thanks Lars, Pretty much what I thought. I don't use zeners or TVS diodes in the unit I build. I use parts that are all rated for high voltage and provide diode protection where required and some other techniques so that if high voltage spikes are encountered, the power supply doesn't multiply them and damage other voltage sensitive parts. Of course, a good filter network at the input is important too as you already mentioned. The lowly resistor is actually a good suppression device too if you don't mind some losses. It's also proportional to voltage so its effectiveness at suppression increases with voltage, without a sudden turn-on like zeners or TVS diodes can create issues and possibly even more spikes when they turn off. Fred
The more I think about, the damage to the transistors most likely occurs from within the unit rather than without, not that damage couldn't result from external voltage spikes. Internal voltage spikes and localized heating in excess of the ratings are most likely occurring every time the oscillator switches. That is, given the nature of that type of oscillator and the slow switching speeds. It's an iron core (if I'm not mistaken?) and will have a very sharply bent hysteresis curve. I'll bet the voltage spikes on transistor turn off are huge and the heating from operating in the saturated region too long is also huge. Fred
Fred, no doubt there are some things that could have been done better, but had there been any serious issues with the design, they would not have lived as long as they have. For a 1967 or -68 design, it looks quite respectable to me. The power transistors available at the time were slow, analogue devices. The high voltage switching transistors we have today simply did not exist, or were prohibitively expensive. The designers did the best they could at the time, and to their credit, many of the Dinoplexes are still running untouched today, almost 50 years later. Andrew, Thanks for the link and info about the ignition coils. I did not know they were refillable. Interesting. Let us know how your rebuild works out, and if you plan to install any protective or upgraded components. Lars
Lars, I had planned to do some meaurements but unfortunately we had a small accident in my workshop this past week involving a broken pipe and the new LCR meter I bought was under it and is no more... I lost about 8 power tools but fortunately I had moved the dinoplex over next to the car so I could run it! Nothing dino related was damaged.
