Perhaps one wrong setting may not be enough to produce such channel imbalance, but combine wrong azimuth, too much or too little anti-aliasing, mis-aligned cartridge, the turntable not leveled, too much or too little tracking force, etc., and it's possible that all this may cause one channel to sound louder than the other.
Also, this channel imbalance could easily be one of the cartridge leads not making enough contact because is either fractured or not seated well.
These wrong settings may cause a singer's voice to be positioned 2/3 to the right or left, instead of in the center of the soundstage.
Best,
iSanchez