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ischmitz ischmitz is offline
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Join Date: May 2002
Location: Santa Barbara, CA
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Rick, I think D401 (47V Zener) is an active flyback clamp. It clamps the flyback spike to something less than the Zener voltage by turning T402 on once the avalance voltage is reached.

T404 in combination with D1 is the flyback damping. See this schematic below "borrowd" from the Megasquirt site. It think it is the same principle shown here from Bowling & Grippo:

For the full description go here. They realized the active clamp with its on transistor TIP42 and use the same flyback damping with the diode FR302 and transistor TIP125 controlled by the processor.
'74 Targa 3.6 (not stock ) - '01 C4 (almost stock) - '00 ML430 (stock)

I repair/rebuild Bosch CDI Boxes and Porsche Motronic DMEs
Porsche "Hammer" or Porsche PST2 - I can help!!
How about a NoBadDays DualChip for 964 or '95 993
Old 04-04-2008, 02:09 PM
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