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Old 06-10-2021, 12:09 PM   #1
roadrash
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Default 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 Images
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File Type: jpg 20210610_182151.jpg (210.5 KB, 24 views)
File Type: jpg 20210610_182123.jpg (189.8 KB, 19 views)
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Old 06-10-2021, 12:23 PM   #2
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Default Re: Motorcycle CDI ignition unit

some copper traces look damaged .
did you try petrol to remove the gloop ?
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Old 06-10-2021, 12:28 PM   #3
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Default Re: Motorcycle CDI ignition unit

remove resin by heating it first, i have de-potted loads of protection devices on arcade boards that way.
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Old 06-10-2021, 04:02 PM   #4
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Default Re: Motorcycle CDI ignition unit

Quote:
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.
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Old 06-10-2021, 04:08 PM   #5
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Default Re: Motorcycle CDI ignition unit

Quote:
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.
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Old 06-10-2021, 04:11 PM   #6
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Default Re: Motorcycle CDI ignition unit

am guessing they run hot
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Old 06-10-2021, 05:42 PM   #7
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Default 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.
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Old 06-11-2021, 01:21 AM   #8
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Default Re: Motorcycle CDI ignition unit

the resistor stacks could be a heat thing, was this in an aluminium shell?
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Old 06-11-2021, 07:28 AM   #9
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Default Re: Motorcycle CDI ignition unit

Quote:
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.
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File Type: jpg 20210611_141513.jpg (596.8 KB, 10 views)
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Old 06-11-2021, 07:31 AM   #10
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Default Re: Motorcycle CDI ignition unit

Quote:
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
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Old 06-11-2021, 07:40 AM   #11
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Default 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.
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File Type: jpg 20210611_134432.jpg (200.9 KB, 11 views)
File Type: jpg 20210611_132028.jpg (240.7 KB, 12 views)

Last edited by roadrash; 06-11-2021 at 07:42 AM..
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Old 06-11-2021, 08:46 AM   #12
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Default Re: Motorcycle CDI ignition unit

put the green to220 devices in a component tester
do you have a wiring diagram for the bike btw?
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Old 06-11-2021, 10:20 AM   #13
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Default 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
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Old 06-11-2021, 10:41 AM   #14
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Default Re: Motorcycle CDI ignition unit

(off-topic) The old CX500 flying maggot , a friend of mine had one of those
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Old 06-11-2021, 11:52 AM   #15
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Default Re: Motorcycle CDI ignition unit

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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.
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Old 06-11-2021, 11:58 AM   #16
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Default Re: Motorcycle CDI ignition unit

351 could be a cap or a temperature sensitive resistor of some type to limit current.
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Old 06-11-2021, 12:40 PM   #17
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Default 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
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Old 06-11-2021, 01:46 PM   #18
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Default 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.
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Old 06-11-2021, 04:53 PM   #19
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Default Re: Motorcycle CDI ignition unit

maybe re-designing it to use mosfets is the answer.
or darlingtons
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Old 06-12-2021, 02:52 AM   #20
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Default Re: Motorcycle CDI ignition unit

Quote:
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.
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