Date:         Sat, 8 Aug 2009 16:15:58 -0400
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Re: 2.1l ECU - Solder Fatigue
Comments: To: pdooley <psdooley@verizon.net>
In-Reply-To:  <0KO0003W1C4H8M5A@vms173011.mailsrvcs.net>
Content-Type: text/plain; charset="us-ascii"; format=flowed

At 09:00 AM 8/7/2009, pdooley wrote:
>Makes me wonder how many Vanagon owners have replaced bad ECU's that just
>had a bad solder joint.

Solder fatigue is a widespread and largely unrecognized
phenomenon.  Predisposing factors are vibration, thermal cycling,
heavy-ish components standing free of the board (typically resistors
expected to get hot, TO-220-case transistors and such), heavy
components in general, components attached to fixed structures like
heat sinks, particularly if there is no stress relief bent into the
leads.  This last is a sure-fire recipe since the leads are unlikely
to expand and contract at precisely the same rate as the heat sink,
and by definition such devices are subject to heavy thermal cycling.

Our ECU is subject to all these factors, including power devices
bolted to a massive heat sink with no stress relief in the leads; so
it's no surprise that it happens -- but it's not just ECUs.  I've
fixed an astonishing number of busted electronics of all sorts simply
by going through the whole board with an iron.  With high-voltage or
-power components, though, sometimes the bad contact itself can
destroy the component.  The ECU driver transistors for FI and
ignition (on the 2.1l) could be candidates for this.

It's often impossible to see without strong magnification -- those
pictures as displayed on a monitor are equivalent to 100x or better,
and I only photographed obvious examples, not the more subtle
ones.  I was alerted to the problem by an article (with much better
photos than mine) in an electronics trade pub around 1980.  That and
an article about fretting corrosion in plug contacts were about the
most valuable things I've read in practical electronics.


>Is this how they "rebuid" ECUs?

I certainly hope so...


  --
David Beierl - Providence RI USA -- http://pws.prserv.net/synergy/Vanagon/
'89 Po' White Star "Scamp"