TRAIN PREP.REPORTED 3607 A1 DOOR OBSTACL ~~~~~ To Follow Up Rectification.  3607 A1 door checked/found RHS roller cracked. Replaced the roller. No FOD found & cleaned the J-rail. Function test - OK.     Alan/Lee PT 44724 3607 TRAIN PREP. REPORTED A1 DOOR OBSTACLE DECTETOR INDICATION LIGHT UP.  3607 checked ER & no FC found. #3607 A1 door after opened fully, OD indicator lit up for a few seconds & self-cleared. Checked door leaf & found LHS sand  coming from the lower side. Weather strip was rubbing against carbody. Trimmed the weather strip & function test door operation - OK. As preventive measure, swapped #3607 A1 door DCP with #B1 door. Door operation check & door cyclic test 10x - OK. OPS 20 raised to investigate further.  Au TK 44723