sampling problems

Tell me this
Should I record from vinyl in Mono or Stereo because when I am recording in stereo The right channel is recorded with good quality but left is very bad is this something possible with mpc when in perfect order or mine is broken. I am recording from turntable via phono preamp build in I am asking because I am going to ged rid of this mpc because the quality is extremly bad. If this is something not right or if I am doing something wrong please tell me I am rcording from stereo record.Ive bought this mpc second hand so I dont know how new mpc is acting.I am 1000% shure that this problem is not caused by trurntable or cartlidge or needle because I have changed few times needdle cartlidge and turntable an the problem is in MPC or I am doing something wrong

Thanks!!!

try sampling from another source(like a cd player or even your smart phone) OR try using the turntable on another sampler/mixer ... Also switch the cable from left to right on the mpc input?
If the problem switches from left to right(in the sample view) then its either a cable or the turntable.. if it doesn;t then it could be the built in pre..