Bad TV picture: is it the aerial, the TV set or the signal?

What exactly are you seeing

Digital terrestrial faults almost always show up in one of these ways: the picture pixelates from time to time, the sound cuts out, some channels have disappeared from the list, or the screen simply says «no signal». Each symptom points in a different direction, so the first step is to be clear about which one is yours.

Intermittent pixelation usually means the signal is arriving but is weak or suffering interference. A complete absence of signal points to a break somewhere in the chain: cable, connector, amplifier or aerial. And losing specific channels while keeping the rest is very often nothing more than an out-of-date channel scan.

Checks you can safely do yourself

All of these are done from inside the home and require no work at height and no handling of the electrical installation.

• Try a different TV on the same aerial socket. If the second set is fine, the problem is the first TV or its set-top box, not the installation.
• Try the same TV on a different socket in the home. If it works there, that particular socket or its cable is the likely culprit.
• Check that the aerial lead is screwed in properly at both ends and that the connector is not crushed or corroded.
• Run an automatic channel scan from the TV menu. If the missing channels come back, it was just a tuning issue.
• Ask a neighbour in the same building. If everyone has the same problem, it points to the communal installation rather than your flat.

When the problem is the TV or the set-top box

If another set on the same socket works perfectly, the installation is delivering signal and the fault lies with the equipment. The same applies when the problem only appears on an external set-top box and not on the TV's own tuner.

It is also the equipment when the picture is fine but the sound fails on every channel, or when the TV loses its channel list every time it is switched off: that is usually memory or settings on the set itself.

Signs the fault is in the aerial installation

There are fairly clear clues that the problem is outside the living room. The most common are:

• Every TV in the home fails at the same time.
• The problem gets worse in rain or strong wind, or appeared right after a storm.
• Several neighbours in the building are affected.
• The picture degraded gradually over months.

The most frequent causes we find

In aerial installations the same faults come up again and again: failed amplifiers, cables and connectors damaged by the weather, aerials knocked out of alignment by the wind and channels left untuned after a frequency change. The repair consists of replacing the affected part and realigning and retuning the installation.

Satellite dishes add one more factor: alignment is far more critical than with terrestrial aerials, and a small shift of the mast or moisture in the LNB is enough to lose the signal.

What you should not do

Do not climb onto the roof to look at the aerial. It is the most common cause of serious domestic accidents with this kind of fault, and in any case you cannot tell from up there whether the problem is electrical or a matter of alignment without measuring equipment.

Nor should you tamper with the amplifier in the communal cabinet or open distribution boxes: in a communal installation, one bad adjustment can leave the whole building without signal.