TC reported prealarm smoke internal at Rear DT car. Staff (YWT) checked and cfm no smoke or abnormal ity. ~~~~~ TC reported prealarm smoke internal at R    3718 Checked from Tims internal smoke pre-alarm-2 fault happen one time only.Checked sensor function ok,cleaned the sensor and    conducted function check ok. Checked by Jack/Sateesh/Koh. 31/01/20