TC reported that the cab door knob was loose and unable to open the cab door from the internal of th e driving cab. ~~~~~ 3506 TC reported cab door knob was cab door knob was loose and unable to open The cab door from the internal of the driving cab. CE checked:Found 3506,A/s cab door unable to open.  Checked 3506 A/S cab door found cable broken. Replaced new upper cable on cab door. Security checked - OK. Function test cab door - OK. Able to open & close from inside & outside. DIR extinguised cab door close. Fault clear. Aliff/Daniel/Redzwan 45215