Gut feel without diving into the TS-50 schematic is that you somehow lifted the ground trace to the volume pot. IOW, it's acting as a series rheostat as opposed to a potentiometer wired as a voltage divider. If that's true you'll get some volume control as the series resistance between the top of the pot and the wiper is increased but you won't be able to bring the volume all the way down to zero if the ground side is floating. You should be able to validate whether that's happening with an ohm meter between the pot's wiper and ground and watching what happens to that resistance as you vary the pot's position. If there's an open between the bottom of the pot and ground it could be internal to the pot if for instance there was excessive heat while soldering in the new part or it could be external to the pot as in a broken trace or bad solder joint. Also, are you certain you replaced the pot with the appropriate taper? It's most likely an audio taper pot (log taper) in this application and using a linear taper pot would cause some interesting volume control problems.