Hyundai Repair: Tachometer not working, transmission control module, sending the signal

Question
I have a 2000 Elantra,AT. The tach worked yesterday but this morning it won't move at all. The car seems fine otherwise. I checked the fuse 10a and it is fine. All other dash functions are working. All warning lights show when you stick the key in like they normally do. Why would the tach stop. I had the timing belt replaced yesterday. Could the mech have nudged something?
Thanks Tim

Answer
The tachometer receives the engine speed signal from the ECM (engine control module), which also reports the vehicle speed to the TCM (transmission control module).  It has the same power and ground as the fuel and temp gauges, so if they're working properly it eliminates power and ground as possible causes (except the remote possibility of a problem with the cluster circuit board).  

Chances are the problem is with the tachometer itself.  If the vehicle speed can be read from the transmission computer, then we know that the ECM is sending the signal and that the wiring isn't shorted to ground.  That would leave only the possibilities of open circuit (in wiring or on the cluster circuit board) and tachometer itself.

I don't think it's possible the mechanic caused this problem.  Nothing involved in replacing the timing belt is anywhere near this circuit.