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Yamaha 5CS Ignition coil

No spark so took off the ignion coil to bench test. My understanding (not necessarily correct) is that the primary winding should be 0.2-0.3 ohms and the secondary winding/HT side should be 5 - 8K ohms. My coil primary winding checks out at approx 0.3 ohms on my digital multimeter but the HT winding is open circuit. I have bought another used coil but when I measure the windings that is also open circuit. I am puzzled and I wonder whether there is some obscure way of measuring the HT side resistance or have I just got 2 dud coils? Is there a way of testing the spark generation off the engine. I could just make and break the primary winding and see if there is a spark produced but 12v and 0.2 ohms is about 70 amps so I hesitate to do that and risk damaging the coil as I do not know what voltage is applied to the primary winding by the engine. generator. Any advice to help me think this through is welcomed.
 
I worked on one recently. Motor would loose spark once it got warmed up. You may test the coil at room temperature, but readings may change as temperatures change. This may not be the case here, but it just enforces the fact that certain diagnostics are not that reliable. I would replace the unit. My spark module was not available, so I went with an aftermarket. The price was about 1/3 of the Yamaha unit. The motor now runs great. Question is ..... for how long?
 
What country are you in? This is a US website. A 5CS was not offered here in the USA.

If you can give me the complete engine ID maybe I can get to a USA equivalent model.

Apply 12 volts to that coil and more than likely it will let the smoke out.
 
The voltage applied by the CDI assembly to the primary side of the coil is 95 ~ 190 volts. But only for a nanosecond.
 
This is a modular unit....okay! Final coils rarely fail. I would more suspect this here baby.
 

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Good idea. But does sproutdreamer have a DVA meter? I am often uneasy diagnosing a capacitor discharge "brain box", by it's discharge. Much better to test other units like trigger, stator, and final coil....then point finger at the "box".
 
Hi Thanks for responses. Engine is uk. The thing is the HT winding is open circuit. The seller says it produces a spark on his coil tester. Can we both be right? What I am thinking is that the HT winding has a break in the winding so read open circuit but the ht spark jumps that gap within the coil so there is a spark at the plug but for how long with a HT spark eroding away at the fine winding wire ends. Is that possible?
 
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An open is a far cry from a resistance of ~ 4000 ohms.

I am having a difficult time imagining a current being induced in an open coil.
 
A gap formed in a break of the coil will likely get worse...the gap will likely increase.
The high voltage has to jump the coil gap AND the sparkplug gap. The spark in the sparkplug gap will be weaker than it should be.
If the secondary (high voltage winding) is open, you need to replace the coil!
 
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