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" |
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