Just wanted to concur that if the KIT display is not functioning AND all connections, pcb tracks pertaining to it are all ok, it will be either IC9 (74LS164 - display data serial to parallel latch) or more likely IC10 (ULN2002 - digit drivers) It is remotely possible that the outputs from IC14 (pins39 - serial clock or 19 - serial data) "could" be at fault or tracks damages, dry joints etc. It is unlikely though as the other functions handled by this IC appear from what you say to be working.