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Join Date: Jun 2010
Posts: 2
Faulty s100 IC on ECU. Rightly stuck

Hi there,

I'm trying to track down a replacement part, the s100 IC, that takes the TDC and speed sensor analog waves, does some conversion, and outputs to the digital interrupts of the 8051. I'm aware it was a custom designed analog IC by InterDesign and no datasheet is available, but is there any source of this part available, or is there any known generic part/work around fix?

The IC is either labelled "InterDesign 8504 2438-03" on 911-MWS-01, or "F12438-03" on 911-MWS-02. I'm guessing the change in "F" prefix is just something to due with Ferranti after buying Interdesign.

Any help would be most grateful.

thanks,
Don

Old 07-11-2010, 06:14 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)
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Join Date: Jul 2003
Location: Glorious Pac NW
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Quote:
Originally Posted by inmetal2002 View Post
Hi there,

I'm trying to track down a replacement part, the s100 IC, that takes the TDC and speed sensor analog waves, does some conversion, and outputs to the digital interrupts of the 8051. I'm aware it was a custom designed analog IC by InterDesign and no datasheet is available, but is there any source of this part available, or is there any known generic part/work around fix?

The IC is either labelled "InterDesign 8504 2438-03" on 911-MWS-01, or "F12438-03" on 911-MWS-02. I'm guessing the change in "F" prefix is just something to due with Ferranti after buying Interdesign.

Any help would be most grateful.

thanks,
Don
Darned if I know. If you're fixated on repairing your DME, this may be a useful insight:

Quote:
I have been trying to come up with a way to use the stock VR sensors on my 944 with MSII. I have a V2.2 board that doesn't have a LM1815 circuit on it. Maybe I could be set up a LM1815 circuit inside of the relay box. It looks like Bosch did the same thing in the Motronic DME at the S100 chip with a F12438-03.
From the Megasquirt forum Megasquirt MSEXTRA and MS3EFI support forum • View topic - 944 VR Sensors


However, if all you want is the cheapest/easiest way to fix your car, why don't you obtain a DME from an age-appropriate VW, Volvo or Bimmer and use the either the complete DME (or just the S100) from that? I built a partial list of the Bosche 3.1 Motronic part #'s for my 944 once - but Pelican has a much better one:

Pelican Technical Article: BMW DME Motronic ECU Swap / Repair

If you provide the link to override the Porsche-specific code on the CPU, this can all be read from the EPROM instead. Any competent DME guy should be able to help with this, and likely give you a better map to boot:

Yet Another Cheap DME Replacement

And check out F.R. Wilk's excellent Motronic site The Motronic Web Site
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'77 S with '78 930 power and a few other things.
Old 07-11-2010, 04:46 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #2 (permalink)
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Hi spuggy,

many thanks for the info and links....that will hopefully do the trick and I'll be back running again.

best wishes,
Don

Old 07-12-2010, 07:55 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #3 (permalink)
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