7-segment display is unstable on my PCB board


So I sketched, printed and soldered a PCB board for the first time. But as you can see on the two attached photos, the 7 segment display turns on and off the numbers (not the dot in the middle). This happens every 30 seconds ish. on for 30 seconds, off for 30 seconds, and repeat. I know it is not my code, since it works fine with cables. Does anyone know what this could indicate, so I know what to look for?:smiley: bad soldering? noise?

on the picture it is supposed to say 11.00 but the zeros are missing a segment down on the left side. I assume thats because of bad soldering, but I dont understand the 30 seconds on and off repeatedly.

Thanks for any replies!

A 30-sec cycle could be an overheating 5volt regulator, because of the voltage on the DC socket being too high.

So how do you power the setup.
Post a diagram, with values.