After closer inspection, I realized that pins one and two were on the same trace. I confirmed this by removing power from the board and testing the resistance between the pins... there was no resistance. After powering back on,
I confirmed that 1 to ground and 2 to ground always showed a full 5VDC regardless of the position of the pot. So I cut the trace between them. After cutting the trace, the voltage on pin 2 ranges from 0 to 5V depending on position of the pot as expected.
But even after all of that, the display still has no contrast. I measured the voltage on pin 3 of the 12864-- the contrast control pin. That pin always shows 4.5VDC regardless of the voltage measurement on pin 2.
I confirmed that 1 to ground and 2 to ground always showed a full 5VDC regardless of the position of the pot. So I cut the trace between them. After cutting the trace, the voltage on pin 2 ranges from 0 to 5V depending on position of the pot as expected.
But even after all of that, the display still has no contrast. I measured the voltage on pin 3 of the 12864-- the contrast control pin. That pin always shows 4.5VDC regardless of the voltage measurement on pin 2.