I'm making a bench PSU. The Arduino runs off the purple 5v standby. The Mega also powers 2 LEDs (normal 5mm clear). The thing is, when I upload the code and watch the screen go through the process, it's bright and visible. But when I turn on the 5v standby (without USB) the text is visible if you try really really hard to see.
The 5v standby is rated at 2 amps MAX. I can't imagine it's the code but would anyone help? Why does USB power allow the LCD to power fully compared to the 5v standby?