It's unlikely that it's a balance problem, since a scanner works with such a wide variety of antennas; tuned for the bands or not, including a simple whip (where impedance for say, 50 MHz would be WAY off).  It's not generally a place to try weak signal reception (hopefully) where impedance really matters.

It could be a weak/dead port on the multicoupler, failed (if it ever worked) connector/coax to the scanner or a dead receiver.  Reloading the programming (and/or firmware) would be in the list of things to try.  Murphy happens (all too often).

Start simple, does it receive weather broadcasts on a whip antenna? Work up from that.  Try another scanner in it's place.  Follow tests in a logical clear fashion to localize where the problem/s lie.

Merry Christmas,

Rick NK7I