1st voltage test

[cornholio]

hi all,
really dumb question to begin.
Im doing the first test on my ms2 v3 board im building and i can only get 2.5v in the 40 pin test.
Power is being supplied via a jim stim.
Is this an easy fix or am i in trouble already.
thanks
chris
sydney
australia

[Matt Cramer]

2.5 volts on which pins?

[cornholio]

When i do the 1-2, 19-20 and i think the 31-32 voltage test they are all around 2.5v

[Matt Cramer]

Let's try a more complete test. 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.

[billr]

"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."

I am questioning that. Aren't S12C, U5 left, and D9 left all one diode-drop (D10) lower than battery voltage?

[cornholio]

Il try the complete test tonight and advise,
thanks for the help

[Matt Cramer]

"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."

I am questioning that. Aren't S12C, U5 left, and D9 left all one diode-drop (D10) lower than battery voltage?

They are. But the voltage ought to be closer to battery voltage than, say, the 5 volt plane.

[billr]

Okay, I understand you were trying to keep it simple, just talking about 5V or approximately 12V. I just wanted to be sure I was understanding the circuit correctly.