tachometer problem
 

I have an intermittant problem with the tach. Sometimes it freezes at approx 4-5K, regardless of what the actual engine rpm is running. There does not seem to be a pattern to the malfunction and it usually corrects itself in a minute or so. Does anyone know where the tach receives its signal? Is it from the CPU or from the ignitor coil? I could not tell from the wiring diagram.
Ron A.