Repair of a digital television set-top box

The park of analog TVs rather reluctantly gives way to digital equipment, gradually occupying the “second” places - in the kitchen, in offices, workshops, garages, etc. Simultaneously with them are transferred DVB-T2 set-top boxes. We have already managed to evaluate the merits of the latter, while some owners also appreciated the disadvantages - the rather low reliability of these devices. As a rule, one of the weakest points of this kind of equipment is a pulsed power supply - most cases of failures are related to the malfunction of the power supply, and the failure of the power supply can lead to such serious consequences that the repair of the device will be impossible. And yet, using the example of two set-top boxes for receiving digital TV, the possibility of self-repairing them will be considered here. The first device - TVK 3101. When turned on, the image had a strong distortion, periodically completely disappeared.A few days later, the prefix began to turn off after a few seconds after the logo of the manufacturer appeared on the screen.
 Repair digital set-top box
The second device is an Oriel 740 prefix. This device is on commands I didn’t react from the remote control, the indicator barely glowed in red.
 Repair of digital prefix
After you open Tia of the enclosures of the boxes, it turned out that in both cases electrolytic capacitors of the secondary power filters were swollen.
 Repair digital set-top box
It should be borne in mind that when working with a set-top box special care should be taken - the rectifier of the primary power supply converts the alternating voltage of 220 volts into a constant value of about 300 volts, and this potential remains at the high-voltage terminals electrolytic capacitors for some time after power is removed - up to several tens of seconds. In the pictures they are located between pulse transformers and plugs of power cords.Before working with the device board, these capacitors need to be short-circuited through a resistor of 51-62 kΩ.
 Repair digital set-top box
Both faulty capacitors turned out to be almost the same - 1000 uF, 10 V. The picture shows one of them. The fact that the cover is barely deformed in appearance should not give you the slightest certainty that the part is in good condition - even if any part of the container is preserved, such a part will have an increased leakage current, which is unacceptable. When replacing, you should select capacitors with the same operating voltage or with a slightly larger one as in the picture - instead of 10-volt parts, 16-volt is shown, and with the same dimensions. Of course, the defective parts should be replaced with new ones, and not used ones, otherwise repair will soon have to be repeated.
 Repair the digital set-top box
After replacing, turn on the set-top box - the indicator lights up brightly, the device responds to the commands of the console, the image is stable. But the repair is not over yet ...
 Repair of a digital prefix
The board has traces of flux - solder paste,rosin ... On such a coating, high-frequency currents can quite easily go wherever they like. As a result, we may get an unstable image with time, noise, etc. troubles. Therefore, thoroughly wash my board with a cotton swab moistened with alcohol or acetone. After such a cleaning, wipe the board with a dry cotton swab
 Repair of digital prefix
 Digital set-top box repair
Installing the board in place, check - it works.  Repair digital set-top box
Now we collect prefix fully and once again check the performance.
 Repairing a digital set-top box
We check the second device in the same way - the device works fine, the repair is completed.
Digital set-top box repair
In conclusion, I will add that the quality of the power supply unit of the antenna amplifier also greatly affects the operation of the prist avki.So, if the capacitance of the filtering capacitor is insufficient, signal loss may occur - there have been cases of complete loss of the channels of the second multiplex. To recognize the failure of the antenna power supply, it is enough to replace it with a DC power source with a voltage of 9-12 volts (for example, a “Krona” type battery or a battery from a computer burglar alarm). If the quality of reception improves, then you should replace the antenna power supply with a known good.

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