CDI Boxes 3PIN

[Alfasrule]

Trying to debug these boxes. Noticed in the schematic there are some measurement points on the Schematic. I can figure out most of them, but some not at all. Is there a document for these measurement points on the circuit?
They are LABELED 1-8 and a 2A & 4A. Fixing Alfa Montreal CDI's which are exactly the same as the Porsche's Fun STUFF!
Thanks

[timmy2]

Have you read this thread?
History of Bosch CDI ... toubleshooting info, parts list changes, and schematics ...

[Alfasrule]

I have that one bookmarked as well as a few others on this forum. I searched and searched and there is NO documentation for these measurement points. Thanks for responding, hopfully someone who has this infomatation will help. I'm sure I can figure it out, but I'll be a quicker for me to debug these boxes. Thanks Again!

[HawgRyder]

Quick suggestion.
Change ALL capacitors for better ones (new of course)...tantalium..etc.
Change SCR to one with at least 20AMP cap (and correct or higher voltage value).
Look over all resistors...change any that are darkened or burnt.
Reflow all joints that look suspect.
Now...test...work?
If yes...clean it and use it.
If not....now you can troubleshoot it...but in my experience...they work.
Bob

[Alfasrule]

HawgRyder did all that you suggested, all the caps were replaced, SCR, 82v Zener etc. The circuit just doesn't fire. Scoped the circuit and the SCR is not turning on. The circuit responds to the input, but I get no voltage or reaction on measurement point 8. Check all the components and they test good. I'll figure it out. Thanks!

[Alfasrule]

Figured out what I needed to know. The box doesn't oscillate when power is applied. I changed every component associated with this Power up. I also checked the transformer's resistance and it measures correctly. Don't get it, not a very sophisiticated circuit. Is there something I'm missing here? Please advise!

[ischmitz]

Maybe share some pictures of the internals of that box. The standard Porsche 3-pin box is a DC/DC converter, a trigger circuit and a switch (the SCR). BTW, I wouldn't replace components unless they are confirmed bad. The SCR for example is extremely hard to match with modern types. If the old one is not shorted keep it.

Am I correct in that your box does the high-pitched whine from the continuously running DC/DC converter? So you should see around 450V at the SCR.

Next, if this isn't a Porsche 3-pin box the trigger circuit could be different: It could be set up to sense a VR signal instead of points. I don't know enough about your Alpha. How does the distributor trigger the box? Does it have points or the coil like the later Porsche with the 6-pin boxes?

Cheers,
Ingo

[Alfasrule]

The setup is exactly the same as the 911, except the Alfa Montreal has 2 Boxes instead of 1.
Even the part numbers match. The unit gets it's trigger when the Points close, grounding input "C". This circuit seems to work correctly. I just don't get the initial oscillation that supposed to occur on power up. I scoped the unit. Wish I knew what I should measure or see on measurement points 2, 2a, and 3. The compents I replaced were bad. The 82v Zenor was shorted. and the SCR was removed, so I had to replace that. Those are the only semiconductors I replaced. I also replaced all the caps. All the components I used were confirmed from other posts on this excellent forum. Thanks for all your HELP!

[ischmitz]

Is the Zener installed with correct polarity. Are you aware these came in both cathode=stud and anode=stud. Next would be to look at the power transistor and make sure it's healthy.