One more update... I can see that the OL (overload) pin is pulled low on the TC14433 on the voltage side, but not pulled low on the current side of the board. Looks like there is a 1M resistor in between the input of the TC14433 on the display board and the divided down voltage coming from the main board. It has a 100nf capacitor on it as well (on the TC14433 side), to act as a low pass filter. With the output voltage set to 0V, I measure 0V on one side of that 1M resistor, and 90mv on the other side. Something seems to be wrong with the TC14433. Any idea where I can source these parts?
Edit: I swapped the two TC14433s and now the voltage reading works but the current reading does not. Problem confirmed. I hate soldering PLCCs...
I really would love to find a source for these. Microchip will sell me 5 at a time for $15 each. Ouch.