Date:         Sun, 7 Jan 2007 18:02:20 -0800
Reply-To:     John Bange <jbange@GMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         John Bange <jbange@GMAIL.COM>
Subject:      Re: Idle Stabilizer Control Unit Reverse Engineering
In-Reply-To:  <Pine.LNX.4.58.0701071309130.17323@kenneke.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

>
> How many folks out there have a *bad* IS control unit? I'd love one to
> verify if it's the transistor that went south.


I have a couple toasted ones Frank Condelli was nice enough to send me last
year for similar purposes. My initial plan was to desolder the parts off one
of 'em and map the PC board traces, then add in the components to get a full
circuit diagram. After a little poking around, though, I figured out that
it's actually a very touchy hand-tuned analog computer. Outstanding design
for its time (mid 80's), but seriously yesterday's news. What takes a bunch
of tense interwoven op-amps to do in analog, only takes a 25 cent
microcontroller to do digitally. The engineer that designed this circuit was
a genius, figuring out a way to "count" revolutions per minute and keep it
steady  without actually having anything capable of COUNTING. I have a
partly done design for a PIC based replacement, but employment issues have
conspired to keep me away from completing it. The big missing piece was the
valve itself and how it's operated. I have no scope to hook up to it to see
how the idle controller opens and closes it. It reads constant voltage on a
meter, so I assume it's using some sort of pulse width modulation, but I
don't know. Perhaps someday I'll have the time and the oscilloscope I need
to look into it.

Anyway, if you want a dead idle controller, I can dig one up and mail it to
you, if you like. Just email me your address and I'll try to find it in my
garage. I'm supposed to send Steve Sandlin four big boxes of foreign car key
blanks I don't need (USPS will be sorry they made those $4.85 flat rate
boxes!), so I'll be at the post office anyway and I'd probably be able to
get it out this week.

--
John Bange
'90 Vanagon - "Geldsauger"
"Staubkess bolt? I have one of those?"