1992 S-10 Blazer tachometer problem

Hello,
Tachometer of 1992 S-10 Blazer (digital dash) has started to act quite strangely. It sometimes works properly, sometimes blinks, sometimes goes
totally blank and sometimes shows full rpm even on idle.
Now, I don't have decent manual or much experience with electronics. Would anybody be able to point out what to check. I think it could be some electronic component in dash about to give up but before I rip the dash open I would like to hear your opinion what might cause such behaviour.
If someone knows how the meter reads the rpm from the engine and can point me to check proper wires/connectors I would be extremely happy.
Cheers,     Boogster
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Good luck with that project...my '92 Blazer did the same thing...I had the display replaced... :-(
js

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