A satellite dish LNB, or "low-noise block-down-converter," is the antenna part of a satellite dish set-up and receives the satellite signals focused by the dish. The LNB amplifies the high frequency satellite signals, and then converts them into lower frequency signals, which can be sent along coaxial cable to the satellite box. As the LNB contains complex electronics, it can develop faults over time, which manifest as losing the ability to view certain channels. In extreme cases, all channels can be lost and the satellite box cannot lock onto the satellite signal. When this happens, the LNB should be replaced, a relatively simple procedure.
Remove the old LNB from the LNB arm. This is the metal arm that extends away from the dish, holding the LNB at the focal point. The LNB is held in place either with a number of screws, which should be removed, or using a plastic locking pin which can be pulled out with pliers, depending on the model of your satellite dish.
Disconnect the coaxial cable that runs through the LNB arm and screws onto the connector on the back of the LNB.
Connect the coaxial cable to the new LNB. The connector on the coaxial cable screws onto the connector on the back of the new LNB. Make sure the connectors are screwed tightly to ensure a good connection. Cover the connector with silicone grease to stop water leaking in to the connection.
Fix the new LNB in place at the end of the LNB arm by replacing the screws or locking pin removed from the old LNB.
Be careful not to move the satellite dish when working on it, as it will no longer be aligned correctly to the target satellite and you will lose the satellite signal.