If there is something that is stopping one channel from working, or makes it a lot quieter than the other channel, it might not be the balance control.
View attachment 124900
This is the circuit diagram that I found online.
The balance control seems to be a linear stereo 100 kOhm potentiometer. If you can find any linear, stereo 100 kOhm potentiometer that fits, you could use that. Although the diagram has two separate part numbers for VR501 and VR502, the parts list says they are one item. A stereo potentiometer is just two potentiometers controlled by a common shaft.
If you want to bypass the control, you could just fit four 50 kOhm resistors. You would need one from each slider to each end.
There are six pins. Do the resisters go from the four outer pins to the two middle pins. I want to be sure I do it right.
It may not be obvious which end the "top" of the potentiometer is, as the top is clockwise for the right channel and anticlockwise for the left channel. Blobbing the wrong end with solder would result in no signal at all.No need to be that 'technical' - simply put a blob of solder between the top and slider of each half of the pot, and leave the pot in place.
Or, if he wants to remove the pot, do the same but place a 100K resistor between top and bottom where each pot was - this is simply to provide a DC path for polarizing any potential electrolytics on either side of the pot. If there are no electrolytics then the 100K's wouldn't be needed.
It may not be obvious which end the "top" of the potentiometer is, as the top is clockwise for the right channel and anticlockwise for the left channel. Blobbing the wrong end with solder would result in no signal at all.
As far as I can tell from the circuit diagram, I don't think that you have to have the resistors at all if you are putting both sides to maximum. You can just cut the resistors and it will probably be at full volume.
My suggestion with four 50 kOhm resistors was to simulate the balance control being in the middle. With the links and the 100 kOhm resistor, that would give the maximum volume on both sides.