I disassembled it and tried finding any unsoldered pins with a needle. I couldn't find any that way; perhaps it was just my inexperience with super small electronics. Should I perhaps try retouching them all with a soldering iron anyway?
no, blanket re-soldering usually ends in tears. you are better off trying to figure out which ONE connection is missing, and at the same time testing the LCD.
you can 'activate' individual segments on an LCD using a 9v battery and a 470k resistor wired in series. i've found that, generally, segments will only flash briefly (they really don't like DC), but it is enough to confirm they are working. do this with the LCD
separated from the meter PCB, but preferably still sitting in the plastic holding frame and with the zebra strips in place.
you need to probe pairs of pins on the LCD (via the zebra strips) until you can find the ONE pin that is common to all the missing segments. IF you can make some segments light up, but NOT any of the missing ones, then the problem may well be with the LCD itself.
cheers,
rob :-)