THE SCREEN ON MY COMPACT MAC IS JITTERING.  (2.5)
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       Nine times out of ten this is a symptom of a failing flyback 
  transformer.  It may be accompanied by high-pitched whines and even 
  the smell of burnt ozone.  This is a warning that the demise of the 
  Mac is imminent!  Turn it off and don't use it again till the video 
  is fixed.  If the flyback transformer is in this bad a shape, 
  chances are that other components either already have failed or 
  soon will.  However many expensive parts of the video subsystem are 
  probably working just fine so this is one common problem that can 
  often be fixed much more cheaply by a component-level repair shop 
  than by an authorized dealer who'll likely swap out the entire 
  video board.