I have a Gen 6 Electronics nr. #0070-003 Mendel - 20100820, EJE Electronics
The board is connected to 12V-60W DC power supply - motors are 2,3A (42BYGHW811).
I have connected all the motors on the board (Molex connectors), software and driver connection works fine.

When I first tried to move engines on X axis, I heard a buzzing noise and engine did not move at all. After reading the Reprap website, I realized that I had to set the voltage on the trim pots. If my calculation is right it should be set to 4V (2,3A / 0,57 = 4,03V). I tried to set the voltage on pot for X axis (TP1) reading was 0,00V. After turning the pot, voltage did not changed. The same thing happened on Z and Extruder connections (TP3 and TP4).

When I tried to set Y pot I could set it to maximum of 3,55V - when I test the movement it worked
So the questions:
What is wrong with TP1, TP3 and TP4 connections that I don't get any readings? How can I fix the problem?
How can I set TP2 to 4V?

Either the motors aren't driving for some reason, (opto's not plugged in right/set up in firmware), or the stepper motors/drivers are damaged. I would have thought it more likely a problem with the opto setup. Don't worry too much about getting the voltage right, the only thing you don't want to do is put too much voltage onto the drivers, as they will burn out. Reduce the trim pots until you can't move the axis, then increase by 1/8th of a turn.