NOTE: If you're not familiar with electronics or working with electrical circuits, please leave this to a qualified technician.
This is the 5 volt circuit (logic) not the (more or less) 20v circuit that fires the head. Also, it is showing low on both the print head and the LCD. This could be your:
A. - incoming voltage - check with a volt meter
B. - power supply - check with a volt meter
C. - cable from the power supply to the Main board - check with a volt meter
E. - Main board - If all else checks out, this is probably the culprit.
Good Luck