CD Ignition Box Repair

[wa3vez]

The 2N3055 transistor has failed in my Porsche 1967 911 box. I have removed all of the bottom screws from the box. Do I need to remove the three set screws on the top? What about the epoxied screw or nut on the top? Thanks wa3vez@comcast.net.

[rick-l]

I don't know but wanted to make sure you had seen this:
History of Bosch CDI ... toubleshooting info, parts list changes, and schematics ...
and
6-pin SC/Turbo CDI unit repair documentation

[wa3vez]

Found info thanks. Although I have repaired many PC boards this unit is built in layers and requires a number of wires that must be unsoldered before you can get to the power transistor and the output capacitor. After essentially taking the entire unit apart you are then confronted with testing for the defective components. Some parts should be replaced just because they have some wear (the output capacitor and power transistor, zener diode for example). You are then confronted with finding replacements for some of them that no longer exist.
I concluded that even though I could easily find the defective components it was well worth the cost of having someone who has all of the knowledge and the replacement parts in stock do the job. So it is off to the rebuilders who will fix, test and provide a warranty. My CDI was not making any whistle and of course no spark for the plugs.

[brp914]

Originally Posted by wa3vez

My CDI was not making any whistle and of course no spark for the plugs.

I got a rblt 3 pin CDI that works great but does not whistle. I would actually like the whistle - partly for the diagnostic aspect but also for the classic old Porsche experience. What makes them do that?

[ischmitz]

The "whistle" is the 3.5kHz of the internal DC/DC converter. It uses a transformer to charge up the main capacitor. Every Bosch box does that to a certain degree. It might just be that yours isn't as loud.

If you got a "rebuilt" box it depends on how that rebuild was done. Maybe the internal got swapped out with something different - who knows.....

[wwest]

The level of noise you experience has somewhat to do with the tightness of the windings and core of the DC-DC inverter's flyback transformer, and maybe even nearby metal objects that are less than tightly secured.

~3Khz rising and falling magnetic field will cause anything "loose" to act as "speaker".