Dude,
When mine does this, I learned of a 'quick-fix', that works for me. Lightly moisten your index finger and with as much pressure as you would use to push the buttons of a touch-tone phone, 'swipe' your finger accross the display. The numbers will disappear for a moment and then, in my case, display as normal. If this doesn't work on the first try, increase the pressure slightly and try again. If this 'fix' fails to bring your display back to normal, then it's probably 'toast'.

Bob

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Bob Jones
Bradenton, FL
'87 560SL-Sold
'99 SL500 For Now