Step-out TC reported that one of the train doors did not open at car 1640 'A' side. Staff(CCK) check ed and confirmed all train doors were opened when at station . TC later reported that one of the train doors did not open ~~~~~ 2639 Step-out TC reported one train doors did not open. Staff(CCK) confirmed all train doors were opened when at station. TC later reported one train door did not open at 2639. Staff(WDL) confirmed one train doors did not open 2639 B1 door. Staff(WDL) assisted to isolate the defective pair of train doors and got staff(SBW) to paste the sticker on the defective pair of train doors.  2639 B1 saloon door found motor faulty. Replaced the door operator assembly. Security/function check - OK. Static check & cyclic test - OK. DIR indication tested - OK.  Kamarul/Shafie/Sugu 44795