TIMS showed 'Smoke external' at front M1car. Staff(YCK) checked and confirmed no abnormality. Rear Train 257 line clear no abnormality from AMK - YCK NB. TIMS showed 'Smoke external' at front M1 car. Staff(YCK) checked ~~~~~ 1566 TIMS showed 'Smoke external' . Staff(YCK) checked and confirmed no abnormality.  1566 FC 735/731/721 registered. Replaced DC-DC converter. Checked external smoke detector, cable gland and for water ingress - OK.    No gasket found on smoke detector terminal. Opr 20 rqised to replace smoke detector. DC-DC converter: Old: A103726 New: A103694 Sarma/Alan/Lee PT 45154 1566 To changeout external smoke detector Replaced new smoke detector and security cx satis. Function cx ok. Notification to CSC: 2517046 Done by: Haslan, Asruddin. 21/8/2023