Bench test for CDI

[inaminit]

Hello- I have a bunch of 3 pin CDI's that I am going to offer for sale. I do not have a CDI car to test them in but I would like to do at least a simple bench test to check for the whistling sound when they are energised. Can I connect terminal B to voltage and ground the case? Will that yield the whistling noise in a good unit? Thanks in advance for your answer!

[gamin]

I would like to know also. I have been told that the above "should" work but I would like to hear from someone who has actually done it. Would rather not fry a perfectly good unit.

[kjchristopher]

Whistling boxes aren't always still functioning. Found that out last week....

Some searches here and I found several threads that, after ten minutes of reading, let me test certain parts (especially he green wire/capacitor) to know for certain before having rebuilt.

[poorshe911]

the "whistling" noise is the sound of the oscillator running that steps the voltage up from 12 volts and charges the capacitor for it to be discharged through the coil. I don't have a schematic in front of me at the moment but, to test it properly you will need to simulate the action of the points and test that the unit actually discharges the cap by detecting the output pulse that goes to the coil. you could use a coil and see if you get a spark.

[E Sully]

HKZ Bob had this picture of his test set up in the Used Parts Forum.

[ischmitz]

It is save to hook up +12V and GND to test the DC/DC converter. No sound meand there is some major damage and most likely burned out components from overvoltage. Especially, if it is a 3-pin box. So whistling is a required condition but not a guarantee for a working box.

Next, do not touch the other terminal (A). In case the main capacitor is short there can be serious high voltage present. Using a full ignition setup (coil, spark plug, trigger) is the only way to reliably test the unit. And then you need to make sure the box doesn't fail under temperature.

Cheers,
Ingo