Other cameras' image is normal, both in daytime and at night, but one or several cameras' image is wrong, such as fuzzy, flickering, snowing, staying black and white in daytime and so on.
1. connect camera C1 to channel A1 with working cable B2 to confirm if it is cable B1's problem.
2. Connect camera C1 to working channel A2 with working cable B2 to confirm if it is camera C1's problem.
3. Connect working camera B2 to channle A1 with working cale B2 to confirm if it is channel port A1's problem.
Please try all methods above to confirm which part is wrong so that we can give you correct replacement.