Of //c's and Self-Tests

[ericb@esl1.tamu.edu (Eric B.)]

  I have a couple of //c's that do strange things in Control-OA-CA-Reset self-
  test.  Instead of the blocky low-res shifting image, I get a goofy hi-res 
  screen with stripes of vertical lines drawn in rows in various places on the
  screen.  About every 1/2 second or so the //c lets out a "click" and a 
  horizontal band of "interference" (about two inches high) goes across the 
  screen.  This goes on indefinitely.

  Funny thing is, both units happily play Taxman II and run Mousewrite.
  What gives?

  As an aside, one of the //c's must be an early edition.  It has a lame kb
  with a reinforcement rod underneath and a backplate that actually snaps
  apart.  The other is a later edition with a black metal base and a 
  backplate that does not snap apart.  

  Thanks in advance.

Eric B.