MSefi.com read only forum (Jan.15,2018)

I have a 3.0 PCB that has served me well for years. But a few weeks ago it died while I was driving. I initially thought the MS-I cpu burnt out, so I replaced it with an MS-II (I needed an excuse) but that did not fix the issue.

When I power the board up on the bench using a simple connection to a 12v supply (I do not have a JimStim) everything checks out and I can connect to and program the board. All voltages look good.

When I put the board in the car, I cannot communicate and pin 1 of U5 shows 4.57 volts. I have checked the wiring harness and the board is definitely getting 12v. There are no shorts or other obvious issues with the harness. I have checked all the diodes on the board and they all check out.

I do not know what to do next. Do you have any suggestions?

Thank you in advance.

To check for a short in the Megasquirt PCB, power up the Megasquirt on a Stimulator or on the car and check the following points for voltage with a multimeter.

You should find the same voltage as the battery voltage on the following points: S12, S12C, the center legs of Q9 and Q12, the left (non-banded) end of D3, the left leg of U5, and the left (banded) end of D9.

You should have 5 volts at the following points: S5, the two +5V holes in the proto area, the right (non-banded) end of D9, the right leg of U5, the left (banded) end of D19, and pins 1, 20, and 31 of the CPU.

Let me know where you find the correct voltages, and where you find the wrong ones.

In the car with the battery reading 11.95v I get the following readings:
12v
S12- couldn't find
S12C- 4.08v
Q9- 4.88v
Q12- 4.88v
D3- 4.87v
U5- 4.08v
D9- 4.08v

5v
U5- 3.9v
+5- 3.85v
D9- 3.9v
pin 1- 3.85v
pin 2- 3.85v
pin 3- 3.85v

Thank you for your help.

Can you check the voltage at the DB37 to make sure it's getting a good 12 volt input from the car's wiring?

I am getting good voltage at the DB37. I pulled D19 based on another forum post and that brought my voltage on the 12v spots up to roughly 9.5. Interestingly, I am getting voltage on all 3 legs of Q9 and Q12.