Date: Thu, 12 Aug 2010 21:56:03 -0400
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: An ECU Thing I Learned Today
In-Reply-To: <AANLkTimah4yY+XcBb_R7u1JQfpiyopg0uWU2KW-ErqZc@mail.gmail.c om>
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At 09:25 PM 8/12/2010 Thursday, Robert Fisher wrote:
>Seriously?
Yes, seriously. There are other things that can happen to an ECU,
but in my somewhat-qualified opinion most of the ECUs out there have
a large number of fatigued solder joints any one of which could
become an intermittent or worse at any time. I base this on
microscopic examination of at least five 022 and one 022D from
various years, plus actual fatigue failures in my '84 1.9l. Not to
mention one in my current '89 which would stop the ignition for half
a second any time the rear end went over a sharp bump. Not
necessarily a big one -- a higher than usual tar strip across the
highway could do it.
> My 87 auto
Lucky you -- no conformal coating to torture you.
> has been bogging down lately when fully warmed up, going from a
> full stop or accelerating out of a turn or what-have-you. The
> tranny isn't slipping, the O2 and temp sensors are new. It seems to
> "get its breath" around the top of second gear and runs normally at
> highway speeds.
If any possibility, swap in another one and see. But in my opinion
you won't go wrong by reflowing some of the joints in there
regardless. The one I did a while ago for Max Wellhouse, I believe I
resoldered 125 joints. To my surprise the ribbon cables connecting
the two boards in the Bosch 022 are a major trouble spot -- much less
so in the Triumph-Adler, which also seems to have better solder in
general. All the Bosch solder looks awful whether it has a problem or not.
>Have you taken any pics or video of the repair process?
I've taken a few pics of what a cracked joint looks like under
magnification. Look here:
http://picasaweb.google.com/dbeierl/SolderFatigue# Use full screen
or you won't see them.
Beyond that, you examine under 40x or so and mark the baddies, or you
do the suspicious ones on principle, or you start at one end of the
board and work your way to the other.
Suspicious ones are any component attached to the heat sink, any
component that's raised from the board, any component that's heavy
whether or not it's pasted down with RTV, any component that's
subject to flexing, any transformer, any axial-lead capacitor, any
component subject to thermal cycling, any chip with lots of leads.
To reflow, you need a sponge, an appropriate iron -- 25 watts or so
with a skinny tip to get down between components and solder pads, and
a stand for it. A temperature-controlled iron would be
wonderful. For a few components that are attached to a ground plane,
a small soldering gun might not be amiss because the ground plane
will suck up tremendous heat and keep your joint from flowing
nicely. .025 or so diameter 60/40 or ideally 63/37 tin-lead solder.
Liquid rosin flux, but since you probably can't get that, RS sells
some flux-in-grease paste that's ok. A solder-sucker may come in
handy. A scriber of some sort in case you bridge two pads and can't
remove the solder -- you can scribe between the pads --
maybe. Desoldering braid can be your friend here, and it definitely
likes extra flux. You need to know at least a little about
electronic soldering.
The tip needs to be shiny-bright. Wipe it on the barely-damp sponge
before each use and don't wipe it after. Put a little solder on the
tip and touch the liquid solder to the joint to melt it. Apply a bit
more solder, make sure it's finished melting, on to the next
joint. Do not ever scrub a joint for any reason. The copper foil
isn't stuck all that firmly on the board, and when it's hot it's
hardly stuck at all. A bit of extra flux on the joint often helps,
and if there's already a lot of solder on the joint you may need to
remove some or all before replacing it. A joint where the solder is
bulging out over the edges of the pad has too much. The finished
joint also wants to be shiny-bright -- you'll easily distinguish the
joints that have already had hand work done on them, they'll look
much better than the wave-soldered ones. Crystallization of the
solder surface (Thank You Bosch) is not in itself a problem. Bad
joints may show up where the lead rises out of the solder, or there
may be cracks in the solder away from the lead, including ones that
completely encircle the lead about halfway down the solder
drop. There's one of those in the pictures.
When I was young and had little tiny eyes I might have done all this
with naked eye. Now I use a loupe or a magnified light or often the
microscope on 7.5x
>Any further damage from continuing to run it?
Not likely. Except for maybe having to walk home. If you solder the
wrong two pads together though, and don't notice and fix it, you
could wreck the thing, either until the pads regain their
independence or permanently.
Yours,
David
