What's wrong with my tachometer?
 

Probably a common issue and probably has been answered many many times over; however, I can't seem to find a solution on line.

The car (1990 1.6 Eunos Roadster) is running fine with MS2 V3.0. The ECU is driving the coils directly, so there is no igniter. I also have the tachometer driver circuit and it uses JS4 for output. I have tried two factory tachometers... the result is the same. Once the ignition is on, the tach needle jumps up and stays in one spot. Once ignition is off, the needle slowly drops back, and remains slightly above its original position. Revving the engine has no observable effect on the tachometer.

Here is a video of the issue:
What could be causing this?

what exact circuit did you built?

this one?

http://www.msextra.com/doc/ms1extra/.../LowVTacho.GIF

Hey, the tacho circuit, along with spark outputs were supplied with the ECU. They were built on an "expansion board?"

You can see it in the photo below (brown wires - tach in/out and red wire 12 V). To my untrained eye, the layout looks similar to the circuit diagram you've posted.

EDIT: I forgot to mention, the tachometer behaves exactly the same even when the tacho output is NOT connected to 1H pin.

https://lh3.googleusercontent.com/A0...=w1177-h662-no

Solved...
 

...by building the circuit below in the proto area. I used the outputs from the high power coil drivers on the expansion board as inputs to this circuit.
Attachment 181866