/diy/ - Do It Yourself

I bought a magnetic Tachometer
I hooked it up and it works fine on its own, it sends the RPM to the little LCD screen

I have a controller board that drives the spindle its measuring, if you send it a pulse signal it will show RPM on the software

I spliced a fork off the signal wire, so black goes to yellow wire/LCD screen and another wire goes to the controller board.

You hook it up to the controller board, it works fine in the software but the physical LCD shows 0
Unplug it from controller board and the LCD comes back to life

Is there a reason why it isnt sending the same pulse down both wires, shouldnt they both work?
What do you think the "CS" hole on the PCB is, is it (or any other blank holes )there an output I can solder a wire into and wire the driver board at the same time?