Problem with Auto-Check System on '89 200q

[Adam Sciortino <A.Sciortino@usa.net>]

The Auto-Check System display in my '89 200q has been troublesome since
1991.  Audi twice replaced a circuit board under warranty in '91 and then
again in '92 which fixed the problem for a couple of years.  Since then, the
system has been inoperative most of the time, but intermittently becomes
operative for periods of a few minutes to occasionally several days.  When
malfunctioning, the display screen shows unintelligible pixel patterns.

Thanks for any advise on the cause and possible fix for this problem.