No announcement yet.

912 no spark

  • Filter
  • Time
  • Show
Clear All
new posts

  • 912 no spark

    In the April edition of Microlight flying theres an artical on page 15 about problems with 912 enines that have not been started for some time..
    Apparently a capacitor in the SMD elctronic module dies. therefore rendering the needing the SMD to be replaced. At considerable expense.

    A friend of mine has this problem. engine not started for 1 year due prop issues.

    ??? why does this Capacitor die.

    ??? we are going to borrow a SMD thats been sat in a box for several years, whats the difference

    ??? how can dealers hold spare SMD,s if they could die..

    Heard mention that the capacitor can be reactivated. how can you do this..???

    Heard there companies that will take the SMD apart and replace the defective part... ???

    rgds trevor s

  • #2
    912 no spark


    Your questions were published in RansMail and elicited one suggestion from one reader (KA):-

    mike hallam.

    "The capacitor sounds like it is not a damp- resistant type, hangars are notorious for condensation, especially on an engine. May well be worth gently baking an old failed box to see if that restores operation. If so share it to help others"


    • #3
      912 no spark

      It would be unusual for a capacitor to be affected by damp ingress, though the module itself will be vulnerable. Electrolytic capacitors (usually the ones that are polarity conscious and have markings to indicate fitting direction) do age and can go low capacity after 5-10 years. Depends on how much the manufacturer is prepared to pay for better quality types. Such caps will 'reform' to an extent when powered up, but the associated electronics might not function correctly in the meantime. I'd have thought that someone could rebuild a module - replacing all of the identifiable electrolytics. (But I'm not volunteering...)


      • #4
        912 no spark

        BBA Reman specialise in ECU reconditioning, IIRC they are in Medway.


        • #5
          912 no spark

          My 912S has resolutely decided not to start. No spark on either side.

          A little history - it was always a bit of a dog to start but then the 912S is and so I bought the soft-start module and it went onto module A. But with the soft start it still didn't want to start and I'd end up using both mags anyway (spin it up and then flick it on). Eventually the sprag was dead and of course during dying it was spinning everything less and less making it worse to start.

          Since replacing the sprag I found it *still* didn't leap into life on mag A alone. But once started (on both) it would be fine and even at relatively low revs I could each mag off without it dying.. but had to be above idle (1400).

          But now the bastard won't start at all.

          And I discovered this thread which describes the problem almost identically:

          Basically the modules have a mode of failure where they will not work at cranking revs but will work at running revs.

          So now I'm wondering if this is what might be going on. I pulled both modules off and tested the resistance between every 2 pins on the input and output side and they are identical or at least within 2%. Rotax don't publish specs for the modules and so it's not possible to determine if they are behaving right or wrong - but if it's a capacitative issue then a simple resistance check won't show this anyway.

          I didn't check the charging coils - I did notice that the two red leads had continuity between them but I didn't check each to ground. They are supposed to be on separate coils though so shouldn't really have continuity... red to red should go through each coil in series (via ground) and so be something like 8 ohms.

          Tomorrow morning I shall check the charging coils and if necessary get an oscilloscope out....

          By the way I also notice that the modules are 700 each!!! HOWEVER - if you buy the new ones with soft start incorporated they are 500 a pair.... go figure!! Perhaps they are no longer made by Ducati who I understand sting Rotax for the ignition parts as noone else was prepared to supply them... perhaps when they were re-engineered to have the soft start incorporated another manufacturer was involved?

          Here's a really useful description of how CDI works in detail


          • #6
            912 no spark

            You might as well not bothering responding. I went to the "other" forum where I got a lot of response very quickly compared to zip in the tumbleweed here. New modules purchased.


            • #7
              912 no spark

              Hi Gwyn,
              In the last 12 months we have had 3 x aircraft have replacement SMD modules. The last about a month ago. All were around 2006 - GCD regs.
              Luckily all could have the 500 / pair replacements fitted with no rewiring.

              Still can not work out while BOTH should fail together - unless one fails at low rpm (ie cranking speed) but works at higher RPM so is not noticed......then the second fails in a similar way - and at that point the problem is noticed.



              • #8
                912 no spark

                That's very interesting Andy as my reg is CDWO... I think you are correct that they fail at cranking speed... that's what I've experienced and I found corroborated from someone on the Internet (Australia I think). So should we be pulling together the failed engine serial numbers?


                • #9
                  912 no spark

                  Hi Guys,

                  I've had intermittent starting problems for the last ~24 months as well with no spark. We've tried just about everything: replaced spark plugs, added a soft start module and slipper clutch, tested the plug cap resistance.

                  Our aircraft is currently C-CIEG, but that's because we got a new wing on the old trike. Previous reg was G-CDVR, so there's a definite pattern here.

                  Looks like I need new SMD modules as well.

                  Out of interest guys - did you get intermittent starting problems previously, where some days it would just be dead (possibly in humid conditions?), and some days it would be fine?

                  BTW - where is this "other" forum? I was wondering why things were so quiet here.



                  • #10
                    912 no spark

                    Thanks Stuart - I've had an email from another chap as well with both having to be replaced... 2005, G-CDTO

                    Almost without doubt your modules are dying.

                    You can unplug the modules though and check the input leads though (in the connector block that comes from the engine - it's the one with 6 wires going into it)

                    If we arrange them like this:

                    where 5/6 are the red wires then 1 to 2 should be about 250 ohms as should 3 to 4. Either 5 or 6 will be connected to the mag switch so check continuity to earth when the mag is on/off. The other red wire (thinner on the Quik) will be the charging coil. Resistance should be about 4 ohms. If you crank the engine over and measure the AC voltage between that pin and ground you should see some! Mine registered about 6 point something.

                    Also - the output connector block has 5 wires - two pairs that go to the coils and an extra which is earthed to the manifold - ensure that there is continuity between that pin and earth on the engine.

                    4 coils and 8 plugs are unlikely to fail!

                    My machine would be easier to start some days than others. And I should also add that as a result of poor starting performance I needed a new sprag and as a result of the old sprag dying without me replacing it I needed a new engine frame. If these ignition modules have been faulty then this has cost me 500 and contributed towards the other 1800.

                    Oh and the other forum is here


                    • #11
                      912 no spark

                      Hi all,
                      I posted this in General chat but thought it applies here as well. So pasted below.
                      Swift 912s wouldn't start yesterday.
                      Today used jump leads from additional battery and cranking speed a lot better, still wouldn't start.
                      Used Wifes hairdrier for a few minutes (on the modules not me !! )
                      Then it started instantly, so It looks like the SMD modules are on way out if not gone already.
                      My engine is Ser No 5649058 manufactured 07/2007 and has only done 290 hours.
                      So this seems to bear out the theory that the modules don't like to be cold and/or in a damp hanger.


                      • #12
                        912 no spark

                        In case this may be of use to any body:-



                        • #13
                          912 no spark

                          Very polite to describe it as a "known ageing characteristic" as opposed to a Rotax-denied series defect.


                          • #14
                            912 no spark

                            Just thought this would be of interest. Had my two modules go dead after a 5 week lay-off following last flight. To cut a long story short,which involved much research and wincing at the cost of new units,I found a company called Carmo Electronics in the Netherlands who said they could repair said units. After a number of e-mails to them asking questions,as I was somewhat sceptical to say the least,I decided to take the plunge and sent the units off. They arrived at Carmo on the Friday morning and on the following Wednesday,they arrived back on my workbench-that's customer service with a vengeance!
                            I refitted the units and they work perfectly and have been doing so for some months now. On asking what the problem was with the units,they said that there were a number of poor quality components that had become defective and they had replaced them with higher quality ones. The units had been cut into but the re-potting was of excellent quality. How they achieved the repair amazes me,but at 160 odd per unit I'm certainly not complaining-1st class I think!
                            So,if anyone else has problems,then I can thoroughly recommend Carmo Electronics.


                            • #15
                              912 no spark

                              Having stripped one example down, I'm frankly amazed that anything is repairable. The original potting compound refused to yield to anything I tried on it.