It may be the MAX1631 or it could be something controlling it that is not functioning properly. Get a copy of the MAX1631 datasheet for the pinouts. I can't remember which pins they are, but check at the pins where the 3 and 5 volts outputs are on the chip to eliminate broken traces to the headers as the culprit. Also make sure the chip is receiving supply voltage at the input pins. There are a few shutdown pins on there too and if they aren't as the datasheet specifies, then the chip won't give you output. If the unit works in the car as I believe you said it was then the chip should be ok as it supplies the whole digital side of the board.

See if you can narrow things down a bit. Just be careful when measuring not to short out adjacent pins.

Stu