I think I shorted my board? Help!

[mccarabin]

Hello. I built my own megasquirt and vehicle had been running great for over a year. I THINK I may have inadvertently back-fed voltage through the relay board not sure of which pin(s). Now the vehicle starts and runs for about 5 seconds and then shuts off. I noticed that the reference voltage decays and then shuts down. Noticed the battery voltage at megasquirt decays and shuts down. Anyone have a clue what I can be doing to troubleshoot this? I'm not super electronic savvy but do have some technical skills. There are no obvious signs of burned/damaged components. I'm running MS/Extra 3.4.2. Greatly appreciate any help or guidance.

[billr]

Remove it from the car and power it up with only +12. ground, and com to the TS computer connected; see if it comes alive like that. If you have a Stim, better yet...

[mccarabin]

I do have a Jim Stim and have done what you suggested. No joy. Reference voltage starts out around 5 volt but within a few seconds begins to decay and then shuts down with daughterboard removed. I have been scouring older posts and think i have found a zener diode D19 is bad and will be picking one up tomorrow. I thank you all for guiding me I have just picked up this hobby again and am starting to remember a few things. I hope this is all I damaged. Thanks to all.

[Matt Cramer]

D19 can burn easily if you accidentally inject 12V into VREF.

[mccarabin]

D19 was the problem. I soldered in a new zener diode and all is well. I am learning.
Thank you