U20 is a ULN2803 chip. If you have not had soldering experience, its probably not a good repair to start on!

If you (or someone you know), knows how to solder, cut the legs off U20 on the board, then desolder the remaining stumps left of the legs and clean the holes out.

Put a socket in place, so that if you need to replace it in the future, you can do it without soldering.

Socket and replacement U20 can be found at Jaycar or other electronics shops

Make sure you change the batteries, and mount them off the board - if they leak, you will be up for more expensive repairs