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Honda CX500 Motorcycle CDI ignition unit

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    Honda CX500 Motorcycle CDI ignition unit

    Hi everyone. Not a old computer monitor this timer its something a bit different.
    This is a CDI ignition unit from a 1980 Honda CX500.
    In 1980 all Japanese bike starting replacing the mechanical contact breaker points ignition system with these fully electronic Capacitive discharge units. But trouble is like all electronic components they fail with age and these CDI units are are no longer available. That's progress they say ??? Luckily I found a second hand one thats still working miraculously so can use that to get readings from.
    Not just that but these CDI units are placed in a steel box and then filled with a resin sealing them tight inside and away from water ingress. I was lucky this one had a slightly softer resin that was almost rubbery and I found I could pick at it with model knives and tiny screwdrivers. It took me 2 days to get it out and then pick away at it to reveal all the components. Many say the main reason these things fail is poor solder joints and they do look a bit rough.
    Well It was inevitable that a few things might get damaged removing all that resin and I broke 4 resistors and slight damage to one diode and one capacitor,
    Here are some photos of the unit at different stages.
    At each end of the board there was a strange twisted wire resistor thingy I have no Ideal of its purpose. There are a few transistors also but they have no markings.
    I managed to remove the resin from the bottom of it revealing the printed circuit as well.
    Please can anyone help me identify any of these parts apart from the obvious resistors etc. None of the caps are marked either but there are no electrolytic ones.
    I removed the two main output Capacitors to get access to the components underneath.
    Please please help guide me to getting this rebuilt with the faulty parts replaced as its the only way this bike will run when this current still ancient unit I am using also fails.
    I have uploaded more pictures at https://drive.google.com/drive/folde...2s?usp=sharing
    Attached Files

    #2
    Re: Motorcycle CDI ignition unit

    some copper traces look damaged .
    did you try petrol to remove the gloop ?

    Comment


      #3
      Re: Motorcycle CDI ignition unit

      remove resin by heating it first, i have de-potted loads of protection devices on arcade boards that way.

      Comment


        #4
        Re: Motorcycle CDI ignition unit

        Originally posted by petehall347 View Post
        some copper traces look damaged .
        did you try petrol to remove the gloop ?
        Yes I noticed there are a few myself. There are also a couple that look like broken tracks but they are not because if you zoom in you can see the green lacquer in the area that looks like a crack.

        I am still puzzled what those 2 strange resistor structures are at each end and what they do.

        Comment


          #5
          Re: Motorcycle CDI ignition unit

          Originally posted by stj View Post
          remove resin by heating it first, i have de-potted loads of protection devices on arcade boards that way.
          Thanks for that stj. You are right when i once tried to do a old honda superdream cdi which had the hard type of resin and I was able to remove it by heating it with a tiny jewelery blow torch and it goes crumbly.
          Can you enlighten me stj as to the purpose of these 2 resistor structures and each end do.

          Comment


            #6
            Re: Motorcycle CDI ignition unit

            am guessing they run hot

            Comment


              #7
              Re: Motorcycle CDI ignition unit

              I have helped people reverse engineer these, they can get weird because of the Japanese design and the many patents that were out there back in the day.
              What part numbers do you have for it? Usually other engines got the same (family) of module. It's a lot of work to recreate one.
              The oddball resistors up in the air are likely for setting the ignition timing advance curve for the module, to match it to the engine and its crank pickup. The PCB shows one as R2 trimpot but the factory just soldered in those parts.
              The green TO-220 parts are likely Hitachi SCR's. The green HV caps around 1.5uF 400V.
              Drawing a schematic is the first step, it's mostly the same circuit 2X.
              I don't know the bike's wiring, if it's an exciter coil plus trigger coil or what.

              Comment


                #8
                Re: Motorcycle CDI ignition unit

                the resistor stacks could be a heat thing, was this in an aluminium shell?

                Comment


                  #9
                  Re: Motorcycle CDI ignition unit

                  Originally posted by redwire View Post
                  I have helped people reverse engineer these, they can get weird because of the Japanese design and the many patents that were out there back in the day.
                  What part numbers do you have for it? Usually other engines got the same (family) of module. It's a lot of work to recreate one.
                  The oddball resistors up in the air are likely for setting the ignition timing advance curve for the module, to match it to the engine and its crank pickup. The PCB shows one as R2 trimpot but the factory just soldered in those parts.
                  The green TO-220 parts are likely Hitachi SCR's. The green HV caps around 1.5uF 400V.
                  Drawing a schematic is the first step, it's mostly the same circuit 2X.
                  I don't know the bike's wiring, if it's an exciter coil plus trigger coil or what.
                  I believe that this is made by Hitachi and has a part number in its case TIA02-14.
                  Attached Files

                  Comment


                    #10
                    Re: Motorcycle CDI ignition unit

                    Originally posted by stj View Post
                    the resistor stacks could be a heat thing, was this in an aluminium shell?
                    No this was in a steel shell like this
                    Attached Files

                    Comment


                      #11
                      Re: Motorcycle CDI ignition unit

                      Here are a few more pictures of the components. The transistors have no markings but some of the caps have very feint ones. One seems to be showing 40mv/ 0.04.
                      I am trying to make a component list right now 1st. There is no reason . I have found once most of the resin is removed surgical spirit softens the residents so it can be wiped off the part.
                      Attached Files
                      Last edited by roadrash; 06-11-2021, 07:42 AM.

                      Comment


                        #12
                        Re: Motorcycle CDI ignition unit

                        put the green to220 devices in a component tester
                        do you have a wiring diagram for the bike btw?

                        Comment


                          #13
                          Re: Motorcycle CDI ignition unit

                          also have this little green thing that looks like a ceramic capacitor and has the number 351 on it. My component tester says it's resistor with value 331.4 ohms is this right?
                          There is a diode to that's tests ok but is this any special type? It has the markings 100 76 and 1R
                          Attached Files

                          Comment


                            #14
                            Re: Motorcycle CDI ignition unit

                            (off-topic) The old CX500 flying maggot , a friend of mine had one of those
                            All donations to badcaps are welcome, click on this link to donate. Thanks to all supporters

                            Comment


                              #15
                              Re: Motorcycle CDI ignition unit

                              Originally posted by SMDFlea View Post
                              (off-topic) The old CX500 flying maggot , a friend of mine had one of those
                              Yep, the CX line was interesting with a longitudinal V-twin and shaft drive, kind of like a Honda version of a Moto-Guzzi, except water-cooled and reliable (at least by the standards of the time). My dad had it's big brother (the CX-650) back in the 80s/early-90s.

                              Comment


                                #16
                                Re: Motorcycle CDI ignition unit

                                351 could be a cap or a temperature sensitive resistor of some type to limit current.

                                Comment


                                  #17
                                  Re: Motorcycle CDI ignition unit

                                  Found a schematic and a bit of info .
                                  http://rajamolor.blogspot.com/2008/0...schematic.html
                                  https://motovillage.org/wiki/hondacx...=CDI_Schematic
                                  https://docs.google.com/viewer?a=v&p...FlNWQzYTA3YWM1
                                  All donations to badcaps are welcome, click on this link to donate. Thanks to all supporters

                                  Comment


                                    #18
                                    Re: Motorcycle CDI ignition unit

                                    The tricky part will be the thermistors. You would have measure their resistance at a few different temperatures to find something that matches. As the SCR's heat up, their sensitivity goes up and the thermistor lowers how much gate drive they get.
                                    I did see a remake of the box called Finnbox G47, the thermistors are on the SCR's tabs.
                                    Attached Files

                                    Comment


                                      #19
                                      Re: Motorcycle CDI ignition unit

                                      maybe re-designing it to use mosfets is the answer.
                                      or darlingtons

                                      Comment


                                        #20
                                        Re: Motorcycle CDI ignition unit

                                        Originally posted by stj View Post
                                        put the green to220 devices in a component tester
                                        do you have a wiring diagram for the bike btw?
                                        yes here is what the tester says.
                                        Attached Files

                                        Comment

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