Lost RPM signal with triggering off the coil? Try this!

[Matt Cramer]

Had a customer I had been emailing comment that he wished something I'd told him was posted on the forum. So, here it is!

If you're set the MicroSquirt up to trigger off the coil, and lose the RPM signal (particularly if you have been following older directions and wired Opto In - to ground instead of 12 volts), here is what to check. The most common component to fail in this circuit is the R20 resistor. It's the big one next to the white optoisolator IC, usually marked "681". You can check it with a multimeter; a dead one will be an open circuit. This resistor can be swapped out with a soldering iron, and the pads are large enough that in a pinch you can get a through hole resistor on there.