1.    Check  the  turntable  surface  for  paint  removing  and 
rusting condition; 
2.    Check  the  locking  screws  on  the  back  side  for 
looseness;   
3.  Check if the chain of locking pin is broken or not; 
4.  Place the turntable in level status, release locking pin, 
push the turntable cover with hand to all directions in 
order  to  check  if  it  moves  smoothly  (if  it  does  not 
move smoothly, please release the fixing screw at the 
bottom, open the turntable and clear its inside).