On this Beko, a fridge that freezes is usually a stuck‑open air damper or a sensor/board mismatch, not the drain or defrost heater. Do a full 24‑hour defrost with doors open, then hold the door switch and feel the fridge vent while changing the setting; if airflow stays strong and doesn’t change, the damper is iced/jammed and needs replacing. Also, double‑check the fridge NTC you fitted is the correct value and in the right spot (Beko mixes 5k/10k sensors; the wrong one makes it overcool) and confirm the PCB is the exact CDA648FS/1 variant/config. I’d skip the drain/heater unless you’re chasing leaks or heavy frost.