Almost ready to power up

[rfeecs]

Since the 7805 can only sink a few mA, it will not be able to regulate without a load because of the 15 ohm resistor. Probably the resistor is added in an attempt to boost the maximum current capability. With almost 12 volts input and 5V output, the load has to sink roughly 450mA before the regulator can function.

As you found, if the load current drops below 450mA or so, the output voltage goes up. Pretty scary regulator design, no doubt to save a dollar or two.

Good thing the 680 doesn't have a low current sleep mode.