Update: I got a new CDI the other day and hooked it up and still no-go. I haven't had a chance to make the LED circuit yet. Will try to do that this week.

 

okay, i put together the LEDs and attached to the trigger and ground wires. During crank, one LED does flash. What's next?

 

This strange. The output of the trigger coil should have symmetry. The leading edge of the raised bump will generate a voltage spike, and the trailing edge should then generate an equal amplitude but opposite polarity spike. Both LEDs should flash, or neither should flash.

Maybe you don't have the two led's wired opposite? Maybe one of your led's is bad?

Hmmm...

Look and see which LED is flashing. Then unsolder it and solder it back in reversed. Repeat the trigger voltage test while cranking the engine:

1) If both LEDs now flash, then one of the led's was wired backwards. The fixture is now working, and you've proved that the trigger pickup circuitry is working.

2) If the LED that you just reversed still flashes (and the other one that didn't flash before still doesn't), then your non flashing LED is bad. Replace it and be sure to wire it reversed from the one that is still flashing.

3) If neither LED flashes after reversing the flashing LED then something is very wrong, and I can't think off hand of any scenario that that would cause that. I think you getting this result is unlikely, but if it does happen we can look further.

 

Please forgive my ignorance, but the schematic you gave me for the LEDs shows a resistor on only one side. The LED that worked was the one with the resistor on the positive side. Doesn't the other LED need a resistor as well? I'm a little confused about that. I have worked a lot with LEDs (basic lighting) and have never been able to run a single LED without a resistor. How much power is supposed to come from the negative side?

With the weather as it is, I have not had the chance to go back out and test the LEDs (I left them there). I will update you as soon as I can get over there. Thanks!

BTW, I had the side cover off and the pickup was a small black thing on a bracket with a little nub coming off the middle of it. It did not look like it was adjustable in any way.

 

That's a good question actually. Yes, you must always have a resistor in series with an LED, and each LED must have its own resistor if the LED's are to be lit up at the same time. That last phrase in underlined italics is the important part that allows only one resistor to suffice in this instance.

Here's what's going on: Note that the two LEDs in the schematic are reversed to each other, and like all diodes they will each pass current in one direction only. If you apply a positive voltage across the LED pair plus resistor, one LED is forward biased, and current flows through it which lights it up. The resistor limits the current to a safe value, which is why a resistor is always necessary when driving LEDs from a voltage source. The other LED is reverse biased. No current flows through this LED, and no light comes out. If you were to disconnect this LED and remove it while the other LED is lit up you would see no change in the other LED or resistor voltages or currents. It is out of the picture for positive voltages applied,

Now reverse the voltage to the circuit and apply a negative voltage. Now the first LED is reversed biased and shuts off (no light and no current passes through it). The second LED that was off is now passing current, lit up, and the current is limited by the same resistor that limited current to the first LED.

Again, note that the single resistor never limits current to more than one LED at a time because only one LED can light up at a time - based on the input voltage polarity.

Now let's consider what happens if the LEDs are *not* wired back to back (reversed). When the voltage is applied in one direction no current flows because both LED diodes are reverse biased and no light is emitted from either LED.

When you reverse the applied voltage both LEDs are given voltage in the forward direction, but one of the diodes will reach its forward threshold first. That LED will hog all the current (limited by the resistor) and the other LED will get only a little, or no current. If the LEDs are the same color and the same brand they will probably both light up, but at widely different brightnesses. If the LEDs are different colors then one will light and the other will be completely off. The threshold voltages of different color LEDs are substantially different. Red is less then Yellow, which is less than Green, which is less than Blue, etc. The lowest threshold color will be the one that lights. This is why all LEDs need to have their own resistor (as you correctly noted for LED lighting systems) whenever the LEDs must light at the same time.

Now I hope you see why I suggested that you reverse one of the LEDs around. If they were wired in the same direction (rather than reversed) it could give the exact symptoms you described. Reversing the LED that lights up would reverse the LEDs to each other and the fixture should start working. If the LED that flashed before still flashes then the one that doesn't flash must be bad, since the one flashing LED proves that both polarities are present (it flashes each way around). So the other LED should have flashed in some way - it didn't - so it is bad.

 

Jollygq,

Check out this thread from today (and links from within this thread to past posts) for a problem similar to yours:

http://forums.atvconnection.com/chin...g-battery.html

Don't let the "battery charge" subject line fool you. It has to do with single spark issues.

 

Here is a link to a similar "single spark" problem on a 150cc buggy:

BuggyNews Buggy Forum • View topic - Spark, but no spark.....

The problem is finally solved about midway down page 3...

There is another similar problem there at buggynews somewhere where the person found metal chips in his stator pickup coil stuck to the internal magnet. I tried, but I couldn't find it....

 

was this problem ever solved? i have a roketa 250 uad that would fire and run for hours, if you shut it off it wouldnt start for days. i checked all wiring and replaced coil, cdi, measured stator and finally replaced pickup. now i have spark only when i let off of the start button

 

Wow that topic sure was made harder than it needed to be... Go through and check and clean all your grounds and connections. Check your wire harness for bad wires..

 

I had the same one spark only right after letting off the starter button, turned out to be the ignition kill wire to CDI, unpinned from the connector, full spark and started. Wire was lightly shorted to ground, I have not figured out where the fault in the harness is yet as im dealing with carb issues. My machine has a AC CDI, I just checked AC output supply during crank and found 50- 60 VAC and checked resistance of the trigger, found it to be ok. unplugged key switch, unplugged handle bar stop switch. Then I found a person who mentioned unpinning it from CDI, rules out 100% nothing is commanding the CDI off. The only thing i cant wrap my head around is why the one park only after letting off starter button.