Re: A35 CDI woes and troubles.

Brian F /
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Note I'm making some assumptions on the CDI circuit design based on what seems to be common in the industry; there's a thousand ways to skin a cat.

My guess is that the most likely component to fail in a CDI box is the Silicon Controlled Rectifier (SCR). Fortunately this is a device that you can test, and it's pretty easy to test with a multimeter, even with it in the CDI circuit.

Assuming:

1) The SCR anode is connected to the ignition coil and the CDI capacitor

2) The SCR gate is connected to a trigger signal, through a resistor

3) The SCR cathode is connected to the bottom end ("ground") of the primary winding on the coil

Step 1: Put your multimeter in resistance mode (use a high range if using a manual meter)

Step 2: Connect the positive lead to the SCR anode, connect the negative lead to the SCR cathode. The meter should show an open circuit (high resistance)

Step 3: Reverse the leads (positive to cathode, negative to anode). The meter should show an open circuit (high resistance)

Step 4: Connect the positive lead to the SCR anode and the SCR gate, connect the negative lead to the SCR cathode. This should turn on the SCR and show a short circuit or low resistance.

Step 5: While leaving the SCR anode and SCR cathode connected to the meter, remove the connection to the SCR gate. This should continue to show a short circuit or low resistance, showing the latching behavior of the SCR (important).

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