TC reported train doors at front DT carA2 did not opened. Staff(CCK) checked and confirmed car 3604'A2' door did not opened. Staff(CCK) later isolated the def ective train door in closed position. TC reported train door ~~~~~ TC reported train doors at front DT car     Checked and found #3604 A2 RHS roller damaged. After door roller changeout: Open Close speed pass: Y FOD found: N Door cycle 20x: Y Rubbing marks: N Door Push/Pull force: ok Door mating gap: ok Check Door Lock Switch red line when door closed - ok Door Lock Switch Cushion Rubber intact: Y Door Close Switch distance from actuating plate - ok Door Wobble: N Rectification Actions: Changed out the rollers at 3604 A2 RHS door. Serviced J-rail and guide rail. Cyclic and static test, door operation was smooth and no abnormalities found and DIR/DMI able to extinguish. Done by: Saini/Haslan Date: 10.07.2023