RAMPS 1.4 test code not working for Z-axis

Hello,

My Z-axis motor is not moving when I run the RAMPS 1.4 test code. I have verified that the motor drivers are not the cause. I have also used a multimeter to check the voltages coming out of the DIR, STEP and VMOT pins. When comparing the voltages from these pins on the Z and X axes (which works), they are identical. Any suggestions would be much appreciated.

Update:
The Z-Enable pin is outputting 2.75V, even though in the test code it is set as "LOW", which should make it 0V. When I changed it to "HIGH", the voltage outputted was 5V, as expected. Following this, I removed the RAMPS board and checked the arduino pin which connects to the Z-Enable pin (A8). This pin outputted 0V when set to "LOW" and 5V when set to "HIGH", as expected, so I'm not sure where this discrepancy is coming from. I have a spare RAMPS board which I tested and had the same issue with, which leads me to believe that something may be wrong with the arduino...

Sometimes the connectors between Ramps and Mega board aren't providing best contact. Maybe contact spray will help? But look for cold solder joints first.