'82 450 Igniter - Repair, Replace, or Make?

[bakalorz]

Thanks again Martin, I'll endeavour to get something wired up tonight and start having a look.

One thing I know for sure is I need to invert the signal as the HEI module fires off the negative going signal. I have verified this by putting a 1.5v AA battery across the W to G terminals on the module.

I got the impression that what you want is for it start running the coil on the positive part of the ramp, dwell while the peak is high, and then fire the coil after the peak as the ramp descends. so on the negative going signal, but using a positive amplification.

[pete]

Ok, did what I could to get stuck into it tonight, minus more cranking to get a better signal read out. I may (slim chance) get an opportunity to try cranking it again tomorrow before I take my wife to an ex-work mate's funeral.

Anyway, I have 270 and 4.7K ohm resistors, BC547's, 135k marked green caps, and 22uF electrolytic capacitors. They're the only capacitors I have that seem suitable, and hopefully I'm right that 135k green caps are 1.3uF. Not 100% sure on the suitability to this application, but I didn't think electrolytics were right.



So, given that it appears at this stage that my pickup coils generate a small but positive signal when a spark should fire, I'm using the single transistor inverting circuit from Martin, and John, I did add R3 (4.7K ohm).





Yes, the connections do look dodgy, but they work. Every time I'm hooking a new circuit up, I'm continuity testing with the mulitmeter.

So, I disconnected the coils and hooked it up, and noticed that instead of about 12.5v being available, the circuit appears to be taking it down to around 11.7v.

Also, I discovered that with R2 being 270 ohm (no 280 ohms in my big pack), the base of the transistor was only at about 0.63v, so I upped R2 to 330 ohm which took it to about 0.7v. I'm guessing I may need bigger still due to the voltage drop to 11.7v.

So, I tried shorting R2 out to ground to generate a spark, but it doesn't seem to do much at all, and in fact after that's done, C on the HEI module stays at about 1.6v and doesn't return to 11.7v.

I hope what I'm saying here is making sense because I'm quite confused by it all still at the moment.

My biggest confusion right now is how the biasing of the base of the transistor works with the pickup coil.

What I mean is... we've biased it to about 0.7v to keep it turned on, which in turn keeps the coil turned on.

When the positive signal comes in from the pickup coil, won't that attempt to turn it "more on" and therefore not turn the coil off and cause a spark?

I realise I'm going to be missing some fundamental piece of electronics knowledge when I ask that question, but my head's just spinning round in circles trying to work it out.

I need to go read through those transistor biasing links again and see if I can soak some of that info in I think.

[pete]

I got the impression that what you want is for it start running the coil on the positive part of the ramp, dwell while the peak is high, and then fire the coil after the peak as the ramp descends. so on the negative going signal, but using a positive amplification.

Hmmm I see what you're saying... most likely I'm conveying information poorly.

What the manual says to do to test the ignitor works is to connect a multimeter on the lowest resistance range from the black/white (common) pickup wire to either the green/white or brown pickup wire that is the input to the ignitor.

Connecting the probes should fire the spark, so the positive signal should fire the spark.

Does that make sense?

If the negative signal should fire the spark, I imagine they would say removing the leads would do that, which is what John and I saw in his manual for the 850 ignitor test.

[pete]

Oh, and of course the other important part is that the negative going signal is what causes the HEI module to turn the coil off and fire the spark, which is the exact opposite to the pickup coil.

[john82q]

I might be wrong (often are) but I was under the impression the IC in the HEI module looked after the dwell based on the frequency of the triggering.

That being the case its input just needs to be held above the theshold (say 1.5 v for arguments sake)and you need is a negative going pulse to make it fire.

data sheet for the chip in the module.

http://www.datasheetarchive.com/MC3334-datasheet.html

john

[pete]

I believe that's exactly right John.

Voltages are mentioned earlier in the thread, above 1.65v to turn it on and below 1.37v to turn it off if I remember correctly.

My tired and worn out brain is not understanding how the signal from the pickup can turn the transistor on to generate the negative signal required...

[bakalorz]

I might be wrong (often are) but I was under the impression the IC in the HEI module looked after the dwell based on the frequency of the triggering.

That being the case its input just needs to be held above the theshold (say 1.5 v for arguments sake)and you need is a negative going pulse to make it fire.

data sheet for the chip in the module.

http://www.datasheetarchive.com/MC3334-datasheet.html

john

from looking at Lou's website, I got the impression that the IC adjusted dwell using the W terminal (which we aren't using in this configuration)

If you only use the G terminal, I think the only think that matters is if the voltage is above or below the threshold.

You still end up getting variable dwell because the faster the bike runs, the bigger (and wider) the pulse from the pickup.

one possible way to reconcile using a negative pulse with the Oscope trace would be to switch the two leads from the pickup, this would make the trace go the opposite way. That would let you use the inverting amp.

Two things I forgot before:

You could replace R2/R7 with potentiometers (500 ohms or 1k or so) to make finding the right value easier (and potentially adjust dwell as its running)

for the non-inverting one, changing R7 works the opposite way around ... raise R7 to turn on the coil, and lower R7 to turn it off.
to test after its built, parallel R6 with an additional 4.7k resistor to turn on the coil, spark should occur when you disconnect the additional paralleled resistor.
(on the non-inverting amp you can't just connect the base to 12 volts, that would smoke the transistor)

[pete]

from looking at Lou's website, I got the impression that the IC adjusted dwell using the W terminal (which we aren't using in this configuration)

If you only use the G terminal, I think the only think that matters is if the voltage is above or below the threshold.

You still end up getting variable dwell because the faster the bike runs, the bigger (and wider) the pulse from the pickup.

one possible way to reconcile using a negative pulse with the Oscope trace would be to switch the two leads from the pickup, this would make the trace go the opposite way. That would let you use the inverting amp.

Two things I forgot before:

You could replace R2/R7 with potentiometers (500 ohms or 1k or so) to make finding the right value easier (and potentially adjust dwell as its running)

for the non-inverting one, changing R7 works the opposite way around ... raise R7 to turn on the coil, and lower R7 to turn it off.
to test after its built, parallel R6 with an additional 4.7k resistor to turn on the coil, spark should occur when you disconnect the additional paralleled resistor.
(on the non-inverting amp you can't just connect the base to 12 volts, that would smoke the transistor)

I think you're both right, in that yes the dwell on the HEI module is adjusted by the bias on the W connector, but there is also dwell in relation to the pickup coil. I don't fully get the whole dwell thing, but I do see that both the W and pickup coil come into it.

Martin, when I hooked it up last night, I was connecting W to 12v like the points setup on Lou's page showed, so was this actually wrong and I should've left it disconnected?

The other thing I'm looking at now is the unconfirmed GS450 ignitor schematic.



I can't read the component values on there, but it seems they use a 1K resistor combined with maybe a 3.8K resistor, a zener diode, and maybe a 0.22uF capacitor to couple the pickup coil to the base of the transistor, and a 4.7K resistor is also used to connect to the collector.

I do actually have some zener diodes, but I don't know what type they are or if that actually matters.

Is it worthwhile trying this setup at all? I can't get my brain around how that should work though.

There is also the attached schematic the German fellow did that uses a 47K resistor in conjunction with a diode to couple the signal to the base of the transistor, and this one I can actually sort of comprehend.

I'm not trying to second guess any of your ideas here either guys, I'm just trying to get my brain around it all and at the moment I'm not succeeding at all.

I also now am thinking that my perceived need to invert the signal is actually not quite right.

For the positive going signal to fire a spark, it needs to turn the coil off, which means the transistor needs also to be off. Does that sound right?

So going just by the German fellow's circuit, normally T1 will be off and T2 will be on, meaning the coil will therefore be on.

When the signal generator generates its tiny positive going signal and therefore raises the voltage slightly on the negative side of D1, this turns T1 on, thereby turning T2 off, and therefore firing a spark by turning the coil off again.

I imagine this is also the exact same theory behind your two transistor setup too Martin, so probably that's what I should've been trying.

Sorry for my confusion here and if it's making you guys confused too...

[pete]

Martin I just realised if I go with your second schematic, I'll be one short on 4.7K resistors, so will it reduce the current too much if I use a 5.6K for R8 or should I go with 3.9K? These are the values I have on hand and all are in 1/4 watt rating.

[bakalorz]

Martin I just realised if I go with your second schematic, I'll be one short on 4.7K resistors, so will it reduce the current too much if I use a 5.6K for R8 or should I go with 3.9K? These are the values I have on hand and all are in 1/4 watt rating.

I pretty much used 4.7k everywhere because thats what Lou used. if R8 is too small, the resistors (and transistor if WAY too small) will overheat. If its too large, it may cause problems providing enough drive to the HEI module. my offhand guess is that <2k is too small ... too large would depend on the module ... It could be 10k, 20k, 100k or infinite ... no way to know without testing, but apparently Lou didn't need it, so you can skip it if you need to. I put it in for insurance, and it makes it possible to test the circuit without having the HEI module connected. It might even be bad and make the circuit not work if it drives the HEI TOO high....
I would probably make it 5.6 k or skip it. If you are making two modules though (for two cylinders) make both the same so they work symetrically

[bakalorz]

I'm going to put my comments in red, cause its otherwise hard to make multiple quotes in the middle of it all

I think you're both right, in that yes the dwell on the HEI module is adjusted by the bias on the W connector, but there is also dwell in relation to the pickup coil. I don't fully get the whole dwell thing, but I do see that both the W and pickup coil come into it.

Martin, when I hooked it up last night, I was connecting W to 12v like the points setup on Lou's page showed, so was this actually wrong and I should've left it disconnected?

No, that was the right way to do it. if W is connected to 12v its effectively not being used. when you use W to adjust the dwell its hooked into the input circuit somewhere.

The other thing I'm looking at now is the unconfirmed GS450 ignitor schematic.



I can't read the component values on there, but it seems they use a 1K resistor combined with maybe a 3.8K resistor, a zener diode, and maybe a 0.22uF capacitor to couple the pickup coil to the base of the transistor, and a 4.7K resistor is also used to connect to the collector.

I can't read it, so can't really comment much, what are the wire colors coming in representing. I got the impression the Zener is not on the input but providing a refrence voltage for something.

I do actually have some zener diodes, but I don't know what type they are or if that actually matters.

The zener value has to be right for it to do what it should, they are NOT interchangeable

Is it worthwhile trying this setup at all? I can't get my brain around how that should work though.

That looks like it is the whole igniter ... you would not use the HEI modules with it.

There is also the attached schematic the German fellow did that uses a 47K resistor in conjunction with a diode to couple the signal to the base of the transistor, and this one I can actually sort of comprehend.

I like the way he couples the signal in, its worth trying replacing the cap and 280 ohm resistor with a diode as he shows as an experiment

I'm not trying to second guess any of your ideas here either guys, I'm just trying to get my brain around it all and at the moment I'm not succeeding at all.

I am not familiar with the ignitior, I started reading the thread to learn more than anything else ... I only started commenting because I thought an Opamp was probably the wrong way to go ... I'm only guessing ... somewhat educated guesses, but just guesses.

I also now am thinking that my perceived need to invert the signal is actually not quite right.

For the positive going signal to fire a spark, it needs to turn the coil off, which means the transistor needs also to be off. Does that sound right?

So going just by the German fellow's circuit, normally T1 will be off and T2 will be on, meaning the coil will therefore be on.

I'm not sure ... His D3 and D4 allow the coil voltage to influence the base of the last transistor, so that may complicate things.

When the signal generator generates its tiny positive going signal and therefore raises the voltage slightly on the negative side of D1, this turns T1 on, thereby turning T2 off, and therefore firing a spark by turning the coil off again.

I imagine this is also the exact same theory behind your two transistor setup too Martin, so probably that's what I should've been trying.

With the two transistor amp, it should be biased so that normally Q4 is off, so that Q3 is on, so that the module is off.
when the signal generator generates its tiny positive going signal it turns Q4 on, turning Q3 off, turning the HEI and coils ON
When the signal generators tiny positive going signal stops, Q4 turns off again, Q3 on, and the HEI kills the current to the coils ... and then it sparks, as the tiny positive going signal ENDS

Sorry for my confusion here and if it's making you guys confused too...

[pete]

Ok wow, I think my head just exploded... but again in a good way

I should've clarified that when looking at the ignitor schematic and the German fellow's circuit, I'm only really looking at the first two transistors as everything after that I expect to be covered by the HEI module.

I just tried cranking some more to get a good signal, and the best I could get was a replication of the earlier positive going 80mV signal.

So, I'll next try with the diode and 4.7K resistor (R6) feeding the base of Q4 (in your second schematic), I'll drop R7, and I'll use a 5.6K in place of the 4.7K R8. I'll leave R5 as is.

And yes, I'll do the 5.6K on both circuits for sure.

I think I got what you're saying in relation to biasing Q4 so it is off.

Also, I really do appreciate your help here, and I'm aware that my lack of understanding is making the whole thing harder than it should be. I have every intention of following through on this and making it work like it should.

Thanks again.

Hopefully I can test again in the next day or two as I need to get ready for the funeral shortly.

[pete]

Sorry, R6 should be 47K rather than 4.7K I just realised... or should it still be 4.7K? His R2 (your R5) are quite different, so I should probably stick with the 4.7K's.

[pete]

Ok, attaching the next schematic to try which is the combination of the German fellow's pickup setup with Martin's setup.

[john82q]

over thinking?

Pete, (and Martin)

I think your making this harder than it needs to be, Pete, your a computer guy down load some SPICE software and have a fiddle with these circuits, and some transistor examples, im sure in no time youll understand better.

I have used LTspice before ages ago, I down loaded a new copy tonight its come a long way. I quickly made 2 circuits, the values (componets) are nothing particular, and thats the value of a simulator, nothing goes pop and you can plug in values based on what you have at hand and work up a solution from there. ( you simply draw the circuit the software does the math) .

"W is normally the terminal providing the bias voltage to the negative side of the pickup-coil."

According to lou's notes W is a reference voltage and can be used for adjust the dwell, tying it to 12 v disables it,just leave it disconnected, don't worry about it till after you get her running.

Now I still belive all you need is a 0 heading pulse attached is how to use a opamp without a negative supply, the zeners optional it is there because I have a bad feeling about the input using 12V.(i could be wrong I there I know sweet FA about the HEI)

V1 is the 12, V2 across pickup, "out to the HEI G" B to 12v and C to the coil (-ve)


Now humour me and try the opamp idea attached...


John