Alpine 7915 Resurrection (Vol Pot)

This unit uses one rotary encoder/pot for volume, bass/treble, balance and fader, I suspect this is defective it will only decrease the values it is set on, vol, bass, treble etc. can be decreased but not increased this leads me to believe the pot is defective. Also when I pulled it out of storage after 10 yrs the pot did work but for some unknown reason I lost control of these functions. The only identifying markings are "ALPS JAPAN" there is a number on the pcb that it soldars to "5919" but I have had no luck with that either searching the major parts houses. Any thoughts on finding the pot or the problem it's self would be appreciated.:spin: