First-aid for set-top boxes

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Although TVs and broadcast-tuner boxes are similar in nature and both are microprocessor-controlled, the latter always seem more temperamental and prone to glitches and breakdown. Here, then, is a run-down on what goes wrong and how to get out of trouble when it does: in the showroom, in the customer’s home and at the repair bench. If in any particular case the advice given here fails to provide a solution, it may well be that the box has a serious internal fault, and thus not be viable for repair, especially as service data and non-generic parts can be very hard to get hold of …


Sometimes a set-top box will refuse to operate at all. If there is no light-up on the front panel, try resetting the processor by interrupting the mains power for a few minutes, then if necessary check the fuses in the mains plug and inside the box. Faulty electrolytic capacitors in the box’s internal power supply can be responsible for this, also dry soldered joints and bad plug/socket connections within or outside the box.

A common symptom is an on-screen caption declaring that no signal is being received. It is probably not going to be due to a faulty satellite. Check that the downlead from the dish is plugged into the box and has no visible damage. See if the dish is damaged, loose or obviously misaligned, then suspect a failure of the LNB (at the dish), the cable or the box itself once you’ve rebooted the latter as described above. Substitution tests are helpful here.

Occasionally one or several channels may be missing. Again, mains re-booting is worth a try, followed if necessary by re-scanning – see the instruction book. If the problem persists the LNB or aerial may be faulty, or the receiver box itself; the best way to check them out is by substitution of a known-good set-top box. If the missing channel/s are subscription ones the card and its reader contacts should come under scrutiny.


If the box is working, but sluggish in its response to commands, check the zapper battery(s) and the cleanliness of the infra-red windows at each end of the link. If these are OK, and a known-good zapper gives no relief, the box itself is responsible. This and slowness to download (e.g.) programme data from the broadcast has been known in some models to be due to faulty electrolytic capacitors – again.

Incompatibility with other gear, such as no auto-switching of a TV, is most often due to a need for menu-led (installation) setting up, while strange on-screen colours, also missing or one-sided sound are usually due to a loose or faulty Scart plug in analogue hook-ups. This cannot happen with the digital HDMI connector which tends to be an all-or-nothing link, so it’s worth checking when the TV screen indicates that it’s getting no signal.

Intermittent faults

Perhaps the most irritating problems are those which crop up spasmodically. Intermittent freezing, ‘blockiness’ and streaking of the picture, accompanied by sound drop-out, is most often due to a weak or (in the case of Freeview) interference-laden signal, see page 34 of the April 2011 IER. Severe intermittent problems arise from poor mains contact, typically at the plug/socket or distribution strip; lesser ones from a half-cocked Scart or HDMI connector, where the trouble may also stem from a dry joint inside the box or TV, behind the socket. Bad soldered connections within the set-top box can sometimes be responsible for this, but don’t delve into it unless you are knowledgeable and skilled.

Equipment substitution

Several times above I’ve suggested checking the receiver, zapper etc. by substituting a known good one, and the same goes for a suspect TV, cable or even dish/LNB/downlead combo by trying the gear at a different location. Substitution is the best and most foolproof method for diagnosis, especially when the faulty item can be made to show its problem at a different site or with different peripheral equipment, representing a positive indication rather than the negative one of all appearing well with a known-good substitute in a situation of intermittent problems.

Good luck with faultfinding, and let me know of any interesting solutions you may find, especially if you encounter them more than once.

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