Measuring the voltage drop across electrical components doesn't match the calculated values
Photo 1. (1) 5 V regulator with no decoupling capacitors! (2) Jumpers to (3) supply from a PCB.



Photo 2. (1) 5V and (2) GND. The guys in forensics lab reckon that the 5 V regulator is being fed from a 5 V supply. This won't work!

Your regulator needs "headroom" to work. If you check the datasheet for your regulator you'll find that you need a minimum of about 7 V for the regulator to work. You've also omitted the decoupling capacitors (which for some reason many beginners feel are an optional extra) so the regulator may go into oscillation. Solution: remove the regulator and supply the breadboard directly from the PCB's 5V and GND terminals.

I can see a USB cable plugged into the board. This means that your breadboard has a ground reference to some external power-supply. If your 'scope is using the same ground reference then you must not connect the ground clip to anywhere other than the 0 V rail of your breadboard.