(ET) Problem with E20

["Perry Cain" <perry suppleye com>]

I just went through this with an E20 I was working on.  I believe the
problem is bad diodes, bad traces, or a really poor connection on card #4.
This is the card that does not have the varistor.  Take that card out.  
Look
at each component and traces very carefully.  VERY carefully!  Some of the
diodes were no good on mine, but they looked ok at first glance.   Also, 
the
traces were broken in one little place.  (Reading glasses helped for my old
eyes)

Look down into the edge connector.  An arc had actually melted one 
connector
of mine.

Symptoms were exactly the same.  Varistor cooked.  When jumpered, it cooked
the jumper.  (I replaced the varistor, then pulled out Card #4.) Three
speeds only.  I ended up spending a week trying to find an edge connector
that would work, finally I just soldered the wires to the card.

What the varistor does is protect voltage spikes.  It "captures" them.  At
some point, over time, it just cannot take it anymore and cooks.  A card #4
problem just speeds this up.