Honda CX500 Motorcycle CDI ignition unit

[roadrash]

Re: Honda CX500 Motorcycle CDI ignition unit

Sorry for nipping off for a bit. I got pursued by a friend to rebuild a 1960's Honda CB72 for him and I've just finished rebuilding the engine and now got it back in and trying to sort out the crappy wiring and switches.
Hey Redwire it's incredible how you understand all this CDI stuff. I wish I could be of more help.
If you could make working CDI unit that would be incredible.

[redwire]

Re: Honda CX500 Motorcycle CDI ignition unit

The weird part is the Left and Right cylinder have different SCR-firing circuits, as far as the gate drive (resistors). The pickup coils are supposedly the same between Right and Left, so this leaves me puzzled why no symmetry. I can't get values for R19 or R21 from anyone's pictures.

The semiconductor shortage is affecting some SCR's. I see some ST parts out of stock until October at Mouser and Digi-Key. On a new PC board I'd go with D2PAK parts because they can run cooler with a little copper pour. Anything that sticks up high on a PC board can't take vibration and eventually breaks off, so SMD is better I think than TO-220 up in the air.

I'm drawing a PCB and have to find an enclosure.

[stj]

Re: Honda CX500 Motorcycle CDI ignition unit

it may be cheaper to use matching scr's given they are probably sold in 5's or 10's

[redwire]

Re: Honda CX500 Motorcycle CDI ignition unit

For reliability, I would have a hard time using the original PCB.
I can lay out a new PCB, it's not that difficult for me. I've figured out all the parts. It doesn't all need to be potted. Like the Finnbox, a bare PCB and waterproof plastic box is good. Just the wires coming in and out need to be sealed up. Keeping it the same as the original design but better new parts. Let me know what you think.

About replacement parts:
The thermistors are the green disks marked "351" and not able to get. They are Hitachi 350 ohms at room temp. It is possible to substitute 470 ohm part such as Vishay NTCLE100E3471JB0, if the 82R is changed. Popular size MF52 or MF11 thermistors hard to find below 1k ohms.
The "351" should go from 350 ohms up to around 770 ohms when cold in a fridge, but touching it will warm it up fast. Freezer should be above 1,000 ohms. It's not important, I figured out the temperature compensation.

The SCR's: BT151-500R (NXP) 500V 12A which is popular for CDI but obsolete now, I would use ST TYN612RG 600V 12A.
The smaller TO-202 SCR is apparently the rev limiter. I think an ST X0402MF would work, 4A low voltage is fine. Finnbox went so small to a 1A TO-92 part I would not do it.

[roadrash]

Re: Honda CX500 Motorcycle CDI ignition unit

I could do with 2 of those SCR';s I have one working one but the legs are broke. I put that Thermister I think you said it was in the freezer for a hour or so but its resistance only changes by 30 ohms. It is this little green thing with 351 marked on it you are talking about??. That PCB was rubbish I had quite a few problems with the plating in some of the holes falling out. I couldn't get it all back in but made sure I soldered the parts legs to both sides of the pcb holes.
Do you think we can get this working as it should? I could pour wax into the plastic tubes when I put them back together and use a hot glue gun to hold others parts stable and then seal it all water tight in some kind enclosure.
Its these unknown SCR's that are the problem right? Be nice if we can use easy to get off the shelf parts. I wish I knew more about what you are talking about but Motorcycles and engines are my specialist area.

[stj]

Re: Honda CX500 Motorcycle CDI ignition unit

funny you should mention it, they use LCSC.
julien illet has done some vids about the process.
https://www.youtube.com/watch?v=xDl1AwAzREc

[redwire]

Re: Honda CX500 Motorcycle CDI ignition unit

I find little mistakes in most of the redo's of the CDI unit.
I have it figured out but I can't read two resistor values that Finnbox guy used, what a hassle.

I looked at doing an all SMT build but there are many high voltage parts which are big size, and it's high vibration and temperature swings. Through-hole is tougher and with no more potting compound, I would go that way with D2PAK SCR's because they look better for heat and vibration.
I never tried a chinese board stuffing house. How do they get the parts, and their SCR's are probably from the bowels of guangdong? LCSC is expensive.

[stj]

Re: Honda CX500 Motorcycle CDI ignition unit

cars wont be a problem, their are several aftermarket ecu's available from megasquirt kits all the way upto the holly dominator beasts!!

[roadrash]

Re: Honda CX500 Motorcycle CDI ignition unit

You guys a really great helping me with this dilemma.
I could just buy a Igntech one but Its too expensive for what it is.
Every bike made after 1980 had CDI ignition and now they are all dying. Won't be many running bikes from this era if there are not alternatives available but all manufacturers are not making schematics of these CDI's so they can be remade. God help modern bikes and cars when their ECU's fail in the future. They will never be classics that run.
Sorry about rant it's so frustrating this CDI issue. Hitachi should make the info available if they haven't destroyed it. I did some more searching and found a forum where a guy has made a working CDI and making all info available incuding PCB details.
Take a read here it's very interesting.
https://www.cx500forum.com/threads/s...options.24593/

[stj]

Re: Honda CX500 Motorcycle CDI ignition unit

if it can be designed small enough using smd parts then you can get the chinese to make the boards for peanuts and even put the parts on it for you.
i think the limit for cheap boards is something like 4inch square.

[redwire]

Re: Honda CX500 Motorcycle CDI ignition unit

I did translate it and read it but it's some Rev. 1.2

I can't make out some resistors values. Other schematics have errors. Sigh.
R21 - goes to D12/C8 left TDC rtd, then to SCR-L gate, maybe 910R?
R19 - goes to D11 right TDC, then to R26, maybe 180R?
These are by where the wires come in and not in pics.
TH1, TH2 - thermistor, maybe 500R?


I don't see the point in reverse-engineering the box, posting pics on your blogs, youtube and then not giving out any schematic or parts list, if you're not going to make and sell the replacement modules? Am I wrong? Then you do improvements and post nothing specific.

[roadrash]

Re: Honda CX500 Motorcycle CDI ignition unit

Think I've found the finbox designers blog
https://tuumaustauko.blogspot.com/p/...itech-cdi.html
Need to use Google to translate Finnish t English

[redwire]

Re: Honda CX500 Motorcycle CDI ignition unit

I got an email response from the Finnbox G47 maker:
"Sorry to tell but I haven't made any cdi units for a long time. The schematic is the thing which I keep with me. It's not very complicated but unfortunately it's the most important part of the process. I think I have told enough in my blog how to make one."

So either we make a PC board or leave it.
OP, take your original PCB and check behind a bright light for knife cuts to the traces, from cutting off the potting compound.

The UF5408 is huge, it won't fit and slower 1N5408 was on the first prototype, then all changed to 1N4007. The HV coil is 430R nominal so it can't put out even 1A. The KILL switch just shorts out the coil.
My change would be some to faster recovery diodes or a little more 2A for the high voltage section.
Japan in the late 1970's did not have great HV semiconductors. Here there are three 600-800V diodes in series, giving 1,800-2,400 PIV which is quite high and slow at 3usec.

The heatshrink just has some resistor in it, to prevent shorts to the resistor next to it. The green thermistor is nearby on the board.

[stj]

Re: Honda CX500 Motorcycle CDI ignition unit

test the thermister by reading the resistance while heating or cooling it.
the "coller" is just insulation - probably to raise it up a bit incase it gets hot.

[roadrash]

Re: Honda CX500 Motorcycle CDI ignition unit

about the fast diodes - UF5408

Thanks a lot thats great! I have now finished testing all components that were on the pcb.

All Diodes test as OK including the white ones.
All resistors are the correct value.
All the original Caps except one were ok.
one SCR faulty.

is this really a thermistor?? It looks like a green cermic cap and it measures 347.4 ohms

I was also wondering what is the purpose of this little coller that you see on some resistors and diodes like the one on the resistor on the right in the photo and is it important?

Do you still want me to measure the one working SCR i have at room temp and in the fridge?

[stj]

Re: Honda CX500 Motorcycle CDI ignition unit

about the fast diodes - UF5408

[redwire]

Re: Honda CX500 Motorcycle CDI ignition unit

These are the parts I would suggest as replacements:
Capacitors
2.2uF 400V PP Panasonic ECW-F4225 LS=25mm bend them+glue, all others almost 1" height w/short leads; RS has long lead Kemet R75MR42204040J. Or CBB22 225J400V.
47nF 400V PP Panasonic ECW-F4473 LS=10mm
47nF 250V mylar MKT Panasonic ECQ-E2473, Epcos B32529C3473, Kemet R82IC2470 LS=5mm

Diodes
Black - not sure what original part is.
I would use 1A 1000V 1N4007, FR107
White - original is either V08G 600V 1.1A controlled avalanche 1600V, V06E 400V 1.1A Hitachi 3usec
I would use 2A 1000V fast-recovery: MUR2100, HER208G, BYV38 etc. (replaces white ones)

SCR (two with tab)
TYN608RG 8A 600V 15mA, TN5015H 50A 600V but cheap, BT151-500 12A 500V, 6015LTP

SCR (one with no tab) - have to think about it.

The black bead part "351" is a thermistor. Can you measure the resistance, I thought around 500R at room temp. Bead thermistors 470-500R@25C Beta ~3450, not critical. Like MF52-501, TDK Epcos B57164K0471J000 (3560K), Vishay NTCLE100E3471JB0 (3977K).

If you want, it is possible to remake the PC board or maybe we should track down the Finnbox guy Andy in Finland? He has a few blogs and I just fired off an email to him.

[roadrash]

Re: Honda CX500 Motorcycle CDI ignition unit

Oh, the heatshrink just has resistors inside. Now I see the nearby two green thermistors TH1, TH2 but I figured out their values, they should be 500 ohms at room temp. and around 1.2k in the fridge.

I have to look at the SCR's because they come in maybe 5 different sensitivities, i.e. IGT 6mA, 10mA, 15mA, 20mA, 30mA and the old green Toshibas I have to dig for. Later I can give a parts list, I have them all figured out.

I would check the 14 diodes (!) the board has too.
I can't see a way to zap the capacitor C7 so either it got stabbed scraping the potting compound off, but maybe it did fail short. The Left ign timing coil connects to it and is supposed to be low voltage.

The cap pictured is a 47nF 400V film cap, best is polypropylene like Epcos B32621A4473K000 or Panasonic ECW-F4473HL. I'm not sure who your parts disti's are in the UK.

I have now finished cleaning and checking all the components and all diodes test as ok.
I think it may be a good idea too replace all the caps unless you think the tested ok film type caps are still good enough to use. A lot of the caps have no markings or they are faded. Are all the large film caps the same 47nf film type. Then its just the 2 other types used like the little rounds green ones marked with a value of 351 and the smaller oblong green caps that just have what seems to be a "N" symbol on them. Then just need to know what type these thermistors are? I can get components from all the usual sources here in the UK like RS, Mouser, Digkey, Farnells etc and of sometimes ebay.

[roadrash]

Re: Honda CX500 Motorcycle CDI ignition unit

damn - typical japanese crap.
doing complex stuff the hard way.

if it was mine i'd run the primary supply through a schotky rectifier into a cap bank, then switch it with a pair of fets.
i would control it with a microcontroller that times the pulse-train and then divides it by 2 to get the split and then add advance-delay based on rpm.

it would of course be better if it had a vac sensor for that so you can create a timing table/curve.
i wonder if it would missfire if you went wasted-spark and just fired both cylinders together??

There is a repalcement CDI that uses thge ignition/battery voltage to power the CDI called a Igntec see here but its quite expensive.

[stj]

Re: Honda CX500 Motorcycle CDI ignition unit

damn - typical japanese crap.
doing complex stuff the hard way.

if it was mine i'd run the primary supply through a schotky rectifier into a cap bank, then switch it with a pair of fets.
i would control it with a microcontroller that times the pulse-train and then divides it by 2 to get the split and then add advance-delay based on rpm.

it would of course be better if it had a vac sensor for that so you can create a timing table/curve.
i wonder if it would missfire if you went wasted-spark and just fired both cylinders together??