Train EB was applied at track circuit NW510 in Auto mode. Released EB - ok. Proceeded in ATPM to nex t station. Train EB was applied at track circuit NW510 in Au to mode. Released EB - ok. Proceeded in ATPM to next station ~~~~~ Train EB was applied at track circuit NW Found FC-740 (Obstacle detected) occurred multiple times causing EB external as per ATS alarm lags.Check & found #3554 B/S cable jack knife lug having signs of oxidation causing resistance fluctuate between 53 ohm to 90 ohm.Clean up & rejoin lugs,ok no further signs of fluctuation across 9152 & 9154. Done by Arthur Sam. 23/12/22