CDI Failures

Veeduber · 2004-04-10T03:45:59+00:00

To All:The CIRCUIT used in the generic CDI modules was quite simple and robust becauseof it. Failures in shipped, manufactured units was rare beause the circuittest was relatively simple: Power it up and you could hear the invertersinging about three octaves above middle C. That said the input-side of thecircuit was working. To test the output you simply unclipped the trigger leadfrom ground. That would cause the SCR to dischrage the capacitor through thelead to the coil or other load. Failures in use were usually caused by over-heating or operator error. I frieda unit crossing Laugna Salida, a (usually) dry lake about 70 miles long. Thedust got packed into the fins to such an extent than the you couldn't even seethe unit. (You can't believe the dust... finer than flour.) Sometimes theheating failures were caused by catching too much air-time. An the cheaplybuilt units, such as the ones from Universal, the heat sinks on the powertransistors are not attached to the case (which serves as the ultimate heatsink) but coupled to it by spring-clips wedged between the case and thetransistor. Depending on the orientation of the clips inside the case, and howthe case is mounted to the chassis, and how much shock-protection the mountingprovides, a hard landing could knock the springs out of position. If theydidn't short-out the circuit board, the lack of thermal coupling wouldeventually cause the transistors to fail... often hours after and miles from,the butt-buster that caused the problem.But the most frequent cause of problems was the guy who put it in wrong. I'veseen them tucked up next to the muffler (so as not to clutter-up theirAll-Original engine compartment), polished to a blinding shine... to match theacres of chrome (and retain lots of heat) and connected in a bewilderingvariety of ways, none of which matched the relatively simple instructions thatcome with the unit. But during the heyday of CDI modules all were offered as kits (Universal did sountil...

Apr 10, 2004 21 Replies

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John Connolly 22 years ago

Sure; but it does depend on the cost of your time (it's different for everyone). Most 18 year olds would never bother, a 25 year old may use a file, and a 50 year old will use a power tool. ;-)

This is just a gross generalization, but you get the idea.

John Aircooled.Net inc.

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John Willis 22 years ago

On Sun, 11 Apr 2004 21:57:54 -0600, "John Connolly" scribbled this interesting note:

Time is one piece of the equation, budget being another!:~)

-- John Willis (Remove the Primes before e-mailing me)

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