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Old 04-19-2011, 06:48 PM
Weekend Warrior
Join Date: May 2010
Posts: 9
Default Keep blowing 4-pin CDI

I have a Yamoto 110 with 4-pin CDI. I get a nice hot spark, starts right up. I keep blowing My CDI. I've been thru 4 of them. They get hot, and die after about 10 seconds.

I've put on a different stator, and have 2 new stators but only 2 CDI's left, so it's hard to trouble shoot.

What could cause cdi overload? I've got a Fluke 177 and willing to test anything. I'm good at troubleshooting 5pin systems, but I'm pretty much lost on this 4pin CDI and 4 wire stators.

I had to splice the stator, which has 2 yellow wires that turn white coming from harness, so I have no idea if it matters which goes where.

I'm getting 12.21v on CDI red/black and 11.43v at crank.
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Old 04-19-2011, 11:37 PM
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Are all these CDI's from the same place? I'm wondering if you have a bunch of CDIs from the same bad batch.

There isn't anything you could do to blow up the CDI so quickly without it also keeping you from getting spark:

1) You have the correct power going in (both by direct measurement, and your CDI works for a while).
2) You have a trigger pulse that fires it coming from the stator. This is a low voltage signal wire that won't hurt anything. Plus the fact that it starts up the quad says that it is timed correctly and is doing what it is supposed to do. Plus the CDI trigger input is most likely protected from transients anyway.
3) The output wire to the coil must be OK also because the CDI starts up the quad.

I can envision assembly problems that will cause CDIs to fail quickly after firing them up:

1) There are many parts in a CDI that dissipate power in normal operation. These are supposed to be thermally connected to a heat sink plate close to the outside of the CDI where this heat can safely escape. But if the assembly house doesn't mount them correctly to the plate, or they decided the plate wasn't necessary, etc. then the CDI works for a while until some part overheats and fails.

2) There is a power supply inside a DC powered CDI that takes 12 volts DC and converts it up to several hundred volts DC. Making an efficient switching power supply to do this can be done, but it is also easy to get a component value wrong and the supply runs terrible. Running terrible can mean it gets way hotter than it should to produce the needed output power. This can be as simple as installing a wrong resistor value. Again, some part overheats and the CDI quickly fails.

When you can buy a CDI with several dozens of parts in it for $10 (though middle men as well), you know they don't spend a lot of time and money testing it thoroughly. They come off the assembly line, they plug them in to a test fixture, they get sparks for 5 seconds, and they ship them. And if a thousand CDIs have the same wrong part installed, a thousand get shipped. And if you bought them together from the same source...

I don not think there can be anything in the stators you have that could cause this problem you are having.
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Old 04-20-2011, 10:01 AM
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I had another thought since the last post...

Measure the DC voltage at the CDI while the engine is running at a fast speed. I just want to verify that the power voltage isn't climbing up to 25 volts because of a bad charging system.
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Old 04-20-2011, 10:14 AM
Weekend Warrior
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I swapped out the stator last night, and that seemed to resolve the issue. If I remember, I was getting 5v on each yellow wire, and only 2 on the one I just put on
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Old 04-20-2011, 12:36 PM
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you'd probably be all set with the 5th cdi- sometimes it takes 5 cdi's to flush out the bugs- just try one more and post what happens.
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