Help with 86 Camaro Berlinetta digital dash

Hello,
My digital dash no longer displays the tach or speedo, everything else seems to work fine. Does anyone know where one can find circuit diagrams (I am a electronic tech)
for this display or perhapes you know what the problem is (I have heard this happens a fair bit - so it must be something common).
BTW: Alldata does not seem to have diagrams of the circuit, just the wiring
thanks for any help you can provide.
Tim
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