Jimstim CPU not lighting LEDs during tach test

[dubester]

Hi, I'm new here. I built a Megasquirt and a Jimstim board for a 7M-GTE in my 77 Celica.
The LED tests of the jimstim have worked fine (for both colors), but the tach signal test produces no flashing of the LED. Power distribution on the board seems fine, with 12v getting where it needs to go, and 3.3v on the correct cpu pins. The tach pot voltage inputs to the cpu are fine, but the output to the tach jumper (pin 15) seems to be doing nothing. I'm going to verify this with a scope at work tomorrow. I ordered another cpu from diyautotune and tried it out with the same results. Nothing has been getting hot. Any ideas as to what is wrong? Do I have a short somewhere that is killing the CPUs instantly?

[racingmini_mtl]

If you've successfully done the troubleshooting tests here, you've already tested that there is no short. It might be a stupid question, but are you sure you're putting the CPU the right way in in the socket?

With the scope, check if there is a signal at the CPU pin and follow the path through the resistor and the transistor. It could be a marginal solder joint at any of those components. Also check the DIP switches and the potentiometers. The schematic is available from the JimStim web page.

Jean

[dubester]

Tracked it down with the scope - the transistor (Q1) was bad. Fortunately I had another 2N3904 on hand and replaced it. Plugged the main megasquirt board in and fired it up without any issues. Got TPS and IAC stepper working today too!