Wierd thermistor issue

I recently swapped my printer from a smart lcd to a graphical lcd and am getting a err:mintemp on boot. It only happens when I'm on the power supply alone . If I plug in the USB after I turn it on, the thermistors both show to the correct temp and the printer will work. If I reset the board after plugging in both USB and power supply the error is cleared.

Wondering what the problem is as I'd like to be able to print off SD only. The thermistor outputs are always getting 5v regardless.

Edited 1 time(s). Last edit at 07/05/2016 05:22PM by Brikloss.

You are overloading the 5 volts regulator from the main board, that's way it works fine when usb cable is plugged. The full graphics display puts too much stress on the little regulator.

Use a separate supply for it using an Lm7805 and redirecting the power from it.

This seems to be the issue from reading similar complaints online.

I'm using a PICA Rev C, so not totally sure how to do that with it.

I'm not familiar with that board and there is little information online, you need to cut the 2 wires that supply the power to the display and using a 5 volts regulator re connect them to your 12 volts supply, best way is to look for the display schematics and find the right pins.