Full graphic controller screen problem

Hello,

I just assembled my first 3d printer, and that's prusa i3. All i working fine, i got everything connected right, but i'm having problem with screen brightness.
When i have my printer plugged only into usb, the screen seems fine al it's working, but as soon as i turn the power supply on (12v PSU) the screen get's brighter. Is it possible that is screen getting to much current or something. I alredy isolated the wires leading to screen since the current going to the stepper's could effect the signal but it didn't work. And i also can't change the brightness on the screen (neither on the pot or inside the program)

The screen only on usb


The screen when PSU turned on.


The printer is working with the screen with or without usb fine, but if somebody knows what i did wrong or if my ramps is somehow broken.

Lp Tomaž

ramps 1.4 elektronic? have power in on 5A and 11A?

Yes and both have 12V from the same powersupply. And Ramps 1.4 with arduino mega. Standard electronics.

hm...
you wanna test your elektronics starting by lcd voltage. should be 5.0V not 4,7 or 5,3
and do this with and without every consumer Bed, Hotend, Motors.

I figured out the problem. The 3rd pin from the right on the lcd the brightness adjustment was not soldered the right way. Repaired it and now is working fine. Thank you for your help !