My RepRap Guru prusa i3 V2 B only works when plugged into my computer

While this wouldn't bother me if my computer were a desk top, mine is a laptop that I use for school, work, and entertainment; thus, I can't just leave my computer anchored to my printer for 8 hours if not more.

When I unplug my computer, the LCD display goes black and all activity ceases with the exception of the fan. When plugged in, the printer functions near perfectly.

Google tells me you have a RAMPS type controller.

On a RAMPS this fault is a dead voltage regulator on the mega, or you don't have D1 installed. (or least likely but has happened, a board fault where D1 is not connected to the mega Vin pin)

The mega can get 5v power two different ways
1) it can take 5v from usb
2) it can take 12v power from the dc in jack or vin pin (ramps uses this pin) pass it threw a voltage regulator to make 5v. (this disables the 5v line from usb)

D1 can be found here, under the X and Y stepper drivers


Edited 4 time(s). Last edit at 11/03/2018 10:03PM by Dust.

It is easy to blow the Arduino regulator when it is using an LCD display--It draws more current from the regulator than it was designed to provide (800mA).
If D1 is intact and operational, then you may have to replace the regulator on your Arduino. One solution is to use an external LM7805 regulator with heat sink, wired as follows:
MC33269D: 1: gnd/adj, 2: vout, 3: vin
LM7805: 1: vin, 2: common (gnd), 3: vout
Therefore for MC33269D(board)->LM7805(external):
1->2
2->3
3->1

The 7805 allows for 2.2A output current and 25V input with proper cooling, so it should not fail a second time.