Faulty LNB Problems: Symptoms, Diagnosis and Fixes

The LNB (Low Noise Block downconverter) is the active front end of your satellite dish. It sits on the feed arm, catches the signal the dish focuses, amplifies it, and converts it to a frequency your receiver can use. When it fails, the symptoms are specific. This guide helps you recognise a faulty LNB and decide whether to replace it.

What Does an LNB Actually Do?

Signals arrive from the satellite at 10–12 GHz. Your receiver cannot handle that — it expects 1–2 GHz (the L-band). The LNB does the translation: it amplifies the faint incoming signal, subtracts a fixed local oscillator frequency, and sends the result down the coax. It also switches polarity (13 V / 18 V) and band (22 kHz tone) under receiver control.

Classic Symptoms of a Faulty LNB

• Complete loss of signal on one polarity or one band, while the other works — half the channels missing.
• Signal that is strong but unquality — strength bar high, quality bar at zero.
• Pixelation that only happens in wet weather — water has got into the LNB.
• Intermittent dropout that comes and goes with temperature.
• A burning smell or water inside the LNB body.

Is It the LNB or Something Else?

Before blaming the LNB, rule out the cheap stuff:

• Check the F-connectors at both ends — 80% of “LNB faults” are just a wet or loose connector.
• Try a different receiver on the same cable.
• Check the receiver's LNB power setting is switched on.
• If you have a DiSEqC switch, bypass it temporarily.

Testing the LNB

Disconnect the cable from the LNB and measure the voltage at the receiver end (it should read 13 V or 18 V when a channel is tuned). Reconnect and measure at the LNB end — if voltage is present but no signal returns, the LNB is likely dead. A multimeter across the LNB output should show a few ohms; a short indicates internal failure.

Common Causes of LNB Failure

• Water ingress through the seal around the connector.
• Lightning surge down the cable.
• Age — typical lifespan is 5–10 years.
• Powering the LNB from two receivers at once.

Fixing It

Once you have confirmed the LNB is faulty, replacement is cheap (under €20) and quick. Buy a matching universal LNB, fit it in the same orientation, and re-peak the skew. You should be back to normal in half an hour.

A faulty LNB is one of the few satellite faults you cannot align your way out of. Learn the symptoms, rule out the connectors first, and keep a spare LNB in the drawer — it is the cheapest insurance you can buy.