Hello everyone, I'm new to the forum,
I built my Prusa i3-mail with ramps 1.4
after installing merlin and have configured it, I used it as management software Repetier host. So far so good in fact the electronics was connected safely and I could just move the motors.
Given the strange movements I proceeded to the calibration of the drivers for the motors.
I measured the voltage between the mass of the board and the screw driver trying to adjust the voltage to 0.4 volts. But I noticed that the measured voltage between gnd screw driver and driver was different from the tension between the screw driver and the mass of the board. The calibration operations were carried out without power. Given that some of the values ??did not change, now all of a sudden I find myself on all the drivers a voltage of 0.15 volts, and does not seem to change the rotation of the resistor. In addition, the card gives me error connection with the software and it does not work anymore. What may have happened? Can anyone help me?
Thank you.

You're measuring a voltage. If you have no power (voltage) applied to your electronics, you won't be able to measure it.