China tach doesnt work

Its in the trash. I kinda destroyed the case opening it as my curiosity got the better of me. I sent a 12v square wave in and probed the path and I got it all the way down to the NPN collector and then out the base. IT still didnt pick up the pulse off the coil negative so I bypassed all the protection (caps, diodes and resistors) and sent the coil trigger to the base an let the smoke out of the chip. Lesson learned. If it dont work, just send it back to Amazon.