What to do if the TV signal is absent

The evening is organized in every detail. Your favorite team is ready to take the field and you can't wait to gather with your friends in front of the television to cheer together. Or maybe it's all set to enjoy the highlight episode of a hit TV series. But the worst is just around the corner: once the device is turned on, there is no TV signal and the images suddenly disappear or are so disturbed that you can't watch them at all.

In cases like this, although your first instinct is to call a specialized technician, you can still intervene yourself. And try, with the right measures, to solve the problem by verifying how and why the satellite or terrestrial antenna have stopped working as they should, and if the criticality is to be found instead in the decoder or in the coaxial cable. In this guide we will find out exactly what we can do in case of no digital terrestrial signal, without resorting, of course for minor failures, to the skilled hands of a professional.

No TV signal: decoder and TV failures

When we have a problem of no TV signal, it is possible that our TV set or the decoder for digital terrestrial television are the "culprits". On the other hand, it is not at all uncommon that a trivial power surge, a disturbance in the general electricity network, a firmware bug or even a wrong command can literally send our device into a state of tilt, preventing the reception of TV broadcasts, both from terrestrial and satellite signals. Alternatively, it could be a damaged antenna cable or an obviously precarious connection. In such a scenario, we can then follow precise verifications and operations, in order to exclude as we go along possible criticalities and malfunctions.

Restart the device

As banal as it may seem, the "golden rule" to follow in case of problems with electronic devices is to try immediately to switch them off and on again. For TVs and set-top boxes, it is generally sufficient to put them in standby mode with the appropriate button on the remote control, unplug them for about a minute and then reconnect them. For Sky decoders, however, the procedure to follow is slightly different, to avoid further damage to the device.

Specifically, for the devices of the giant of on-demand television, as indicated in the user manual provided in the package, you should go to the My Sky screen, at this point turn off the decoder, unplug the plug from the power outlet, and hold down the "OK" button on the remote control while reconnecting the plug and until the yellow/orange LED lights up. If we have done everything correctly, let's wait for about ten seconds and hold down the power button of the decoder until the green button lights up.

Check the wiring

In many occasions, when the TV says "no signal", it is possible that there is a break or leakage - even partial - of the coaxial cable from its connector. To remove any doubt, just proceed with an easy check: gently unscrew the F plug (SAT), alternatively there could be an IEC plug (DTT) to pull, check the connections and the position of the central pole and the external braid, called shielding in technical jargon. For the F plug, the central pole is visible and placed in a straight way, while the braid should be on the side, almost completely inside the connector. Check now that everything does not touch the central pole on the side of the threaded ring nut, so as to avoid dangerous short circuits.

This is because some F plugs are screwed on the coaxial cable, and with the passage of time or with the movements of the same cable tend to loosen. If this is the case, we proceed to screw it back until the dielectric of the cable, i.e. that sort of "sponge" which insulates the braid from the central pole, appears inside the F connector on the side which is to be screwed to the TV or decoder.

If these steps should not be possible, the only solution is to cut the coaxial cable and reinsert it into the connector once it has been "stripped". On the other hand, in the case of no TV signal on terrestrial channels with the presence of an IEC cable that can be disassembled, we must necessarily verify that the central core of the coaxial cable is well welded to the central pole, and that the braid is in contact with the external shield and the central pole at the same time. On some occasions the TV antenna cable may not be inspectable: change it for a new one with the same type of plugs, i.e. male-male or male-female.

Reset and retune the channels

Does the problem persist after inspecting the wiring and restarting the TV/decoder? A reset may be the answer we're looking for. The operation brings the device back to factory conditions, the same as when we bought it, consequently eliminating all the changes made to the different available settings, such as account, audio, video or minors restrictions, including the general channel list and favorite ones. To do this, we can use the OSD menu or follow the sequence of buttons indicated in the instruction manual.

For most Sky decoders, we must first unplug the power supply, hold down the "TV Guide" button and at the same time reconnect the plug until the LED flashes yellow. Then wait 30 seconds and restart the decoder with the "Sky" button on the remote control. Now you can restart the decoder and start the automatic retuning of the channels, only for Sky users, or follow the initial installation procedure and carry out a channel search on all the satellites affected by our dish.

No TV signal: problems with antenna sockets, splitters and shunts

Faulty sockets and splitters can also be the cause of weak signals, square images or even no TV signal in the most critical scenarios. To make it easier to solve the problem, in cases like these it could be of great help to have a field meter, even a handheld one. This is an instrument that detects the level and quality of the terrestrial and satellite signal. In any case, the check to be done before proceeding with other possible operations is to check that the coaxial cable that connects the wall antenna socket to the decoder or to the TV has not been damaged. It is in fact not so rare that cleaning or moving furniture go to pull the wiring, loosening it and causing various malfunctions. The steps to follow are exactly the same as we used to check the wiring of television and decoder.

Secondly, we should also inspect the antenna socket. Usually, in apartments we can find them in walled boxes, where they can be injured and crushed. To check for damage, simply remove the plate and inspect the back of the socket. Unscrew the screw terminals and check the condition of the cable and connections, paying attention to any short circuits between the central pole and the braid. If necessary, cut, strip and reinsert the cable in the antenna socket. With the field meter we were talking about, we check that the level of the output signals from the socket is higher than 45 dBµV, in case of a terrestrial signal, or 47 dBµV, in case of a satellite signal.

If the level is lower, we proceed with the measurement on the coaxial cable entering the socket, well recognizable because it is the one coming from the switchboard or from a divider/derivator. When these components are damaged, it may happen for example because of a lightning strike during a thunderstorm, the reception of SAT and/or DTT signals may be completely compromised, forcing us to replace the entire system with a new piece with the same electrical characteristics, usually reported on the casing of the socket.

Just talking about splitters and derivatives, it is important to keep in mind that in certain types of wiring can be connected to the wall antenna socket or to the coaxial cable that goes directly into our apartment. They are particularly useful for dividing the terrestrial and/or satellite signal, to serve multiple outlets that are located in other rooms or multiple nearby appliances in the same room. The splitters and shunts can be of external type, or alternatively be found in the junction boxes.

In both cases we must check the connections between the cable and the connectors, whether they are F or with the more classic terminals,- and then proceed with the actual measurement. Also here, we use a field meter, with levels that, as already pointed out for TV antennas, should be at 45 dBµV, in the presence of a terrestrial TV signal, and at 47 dBµV, only in case we are using a satellite signal. The difference is that it is also necessary to take into account the pass or shunt attenuation of the single divider/derivator, fixed indicatively between 4 and 20 dB.