Do-it-yourself repair of digital television receivers. Why digital TV doesn't work
Greetings, dear colleagues!
Today I will briefly tell you and show you the main problems with digital television DVB T2 set-top boxes.
As an example, I will present to you the receiver from my previous article entitled: "
I'll start in order of priority.
1. Thorough check of the power supply.
First of all, we check the fuse; if it is intact, then we check the power at the output of the power supply. Next is a diode bridge, an electrolytic capacitor after it, and a PWM microcircuit. The output diode and capacitor are located after the pulse transformer. An optocoupler, less often a zener diode, a powerful resistor in the power part of the power supply unit, an adjustable zener diode (installed after the pulse transformer).
2. The receiver freezes.
The LED blinks and lights up dimly. We are trying to supply 5 volts from an external DC source, with an output current of at least 1.5 amperes, to the output capacitor of the power supply. If it starts, then the problem is in the power supply.
The output capacitor of the power supply unit most often requires replacement. 
3. There is 5 volts at the power supply output, but the receiver does not start.
We check secondary DC-DC voltage converters. On the board they usually look like small pentapod microcircuits installed next to the inductors. We measure on inductances 1V, 1.2V, 1.3V, 1.8V, 3.3V, 15V, etc. If it is missing, we change the corresponding microcircuit. 
4. Cyclic reboot, freezes during loading, etc. (the firmware crashed).
In the presence of normal voltages on all pentapods, as well as when the inscription “ASH” appears (in some receivers), cyclic reboot, freezing during loading, etc. - flash the flash memory chip. 
5. Doesn't pick up channels.
Checking the antenna! We reset the settings to factory defaults and start the search again.
The problem may be in the quartz installed in the tuner, if any. If not quartz, then the problem is probably in the tuner microcircuit, demodulator (they are installed in the tuner), or tuner processor. In such cases, repairs are considered difficult and expensive! Weigh the pros and cons.
Don’t rush to change the firmware from a USB flash drive, because you may end up with unnecessary problems and will have to buy a programmer. 
6. There is no color image on the analog video output of the set-top box (RCA, i.e., tulips").
With this malfunction, the quartz installed near the central processor often dies. 
7. The image jumps and twitches, the color is distorted.
The culprit is an electrolytic capacitor located at the rear wall, near the analog video outputs. 
8. There is no signal from the analog video output. There is HDMI video output.
If the cord is in order and so is the socket, then most often this is due to burnout of the analog video signal outputs installed in the processor. Some set-top boxes have additional stages installed between the video output and the processor - check them. If there are none, then you are left with viewing via HDMI, or replacing the central processor.
To prevent this from happening, do not connect the switched-on set-top box to the TV while it is on. Those. so-called “hot plugging” is prohibited.
9. The receiver lives its own life (it turns itself off!).
The problem often lies in the receiver settings. Look in the menu, in the additional settings for the item: “Sleep timer” or something like: “Turn off when inactive.”
10. There is no sound when playing movies from a USB flash drive.
The problem often lies in the processor, i.e. in the absence of a hardware (hardware, not software) Dolby Digital decoder (aka AC3 codec). One solution is to record movies with other audio codecs. Or remove the signal from the set-top box via HDMI and send it over a cord to a device that can decipher this digital audio stream and play it on audio speakers (speakers).
11. Problems with updating the firmware from the air.
When the receiver tries to update the firmware over the air, it freezes severely. Leave it on for half an hour. Not finding the update, it will reboot and continue working as usual (“roll back”).
12. The receiver itself reboots when you start searching for channels, inserting a USB flash drive into it, or in other extreme modes.
The problem often lies in the secondary converters (“five-legged”) and their wiring. Those. they cannot produce the power they are supposed to (they sag").
Many of our compatriots have already been able to verify that digital television produces an image on the screen of better quality than an analog signal.
In order for your home to be able to receive digital channels, you need:
- a regular decimeter antenna;
— DVB T2 receiving set-top box, or receiver;
— a television tower transmitting a signal in DVB T2 format, within the reach of the antenna.
So, you have all this installed, connected (except for the tower, of course) and even worked for a while, but suddenly the signal disappeared. What could be the reason and how can I fix it on my own?
No signal from TV tower
Sometimes the lack of a signal is explained by the simplest reason - the TV tower is not transmitting it at the moment. For example, maintenance work is being carried out or equipment malfunctions have forced the broadcast to be suspended and repairs to be carried out in earnest.
Digital television is still a fairly new direction, so the signal transmission process is not ideal everywhere, and there are failures and breakdowns of equipment.
Poor signal reception conditions
If the signal is received on a weak antenna without an amplifier or with a low-power amplifier, or if there are high-rise buildings or other noise-producing structures in the space between the antenna and the TV tower, the signal may periodically disappear when atmospheric conditions deteriorate. 
In other words, during rain, thick fog or snowfall, severe signal interference occurs. In this case, purchasing a more powerful antenna or moving the existing antenna to the highest possible height to ensure direct visibility of the tower can help.
This is easy to do if you attach the antenna to the roof of the multi-story building in which you live. If this is not possible, then you need to buy an antenna with a powerful amplifier.
Receiver failure
Inexpensive Chinese-made set-top boxes can present similar surprises from time to time - they spontaneously disconnect from signal reception. In this case, the following message appears on the screen: “No signal.”
The simplest action - turning off, and after a few seconds turning on the digital set-top box - often returns the set-top box to working condition.
Poor quality receiver firmware
This defect is most typical, again, for inexpensive Chinese equipment. The only way out is to flash the console's processor. 
You can download the required firmware version from the receiver manufacturer's website, but it is not so easy to do this at home and without certain skills. Most likely, you will have to contact a workshop for this.
Spontaneous reset
Sometimes technology presents such surprises as failure of channel settings. In order to restore the settings, you just need to run auto search, and all available channels will be restored in a few minutes.
Problems begin when the auto search could not find a single channel. In this case, you should repeat the search manually and make sure that there are no even weak signals, which are usually ignored by the auto search.
To check the signal level, you need to find the “INFO” button on the remote control and press it three times in a row - the screen should display information about the signal strength as a percentage of the required one. If the signal is really very weak, you will have to buy an amplifier or move the antenna higher.
Set-top box malfunction
The simplest and most obvious case is that the console has failed for some reason. This could be a power surge, a lightning strike on an antenna on the roof, etc. 
, most likely, does not display any messages on the screen at all, even about the absence of a signal. It may not even turn on. In this case, only contacting a repair shop or buying a new receiver will help.
Since the late 90s of the last century, audio-video technology has evolved greatly. From VCRs and DVD players, CD and MP3 recorders, to omnivorous media players that allowed you to read media files from a USB flash drive. Such devices at one time cost 3-4 thousand.
Now every DVB-T2 receiver can do this. The receivers are quite cheap - from 900 rubles, and in addition to reading media files from a flash drive, they allow you to watch television for free in digital quality, even if only 20 channels. And everything would be fine if the Chinese, in pursuit of cheap devices, did not put low-quality parts there. I have had cases where, in a receiver with a built-in power supply, after 2 years of operation, a small electrolytic capacitor had .
Small electrolytic capacitor
And accordingly, the receiver did not turn on, after measuring the equivalent series resistance ESR with a meter, and replacing the three-ruble capacitor, everything returned to normal and the receiver turned on. But this, as they say, was just luck. Much more often, DC-DC converters burn out in receivers. Sometimes, fortunately for the user who decides to independently repair the set-top box, stabilizers with 3 legs are installed instead; replacement is not difficult, but sometimes the boards have unreliable five-legged converters, and we will analyze this case. There are 3 of them there - small microcircuits in the SOT-23-5 package.
Chip Converter - drawing
They produce, respectively, 3.3 volts, necessary to power the RAM chip, 1.8 volts and 1.2 volts, necessary to power the processor.
Converter chip dimensions
It is easy to determine where the output of the microcircuit is, even without having a datasheet for this microcircuit; the output of the converter can be connected by a track to the inductor necessary for the operation of the converter. You can familiarize yourself with one of the typical converter circuits by looking at the figure below:
What if your set-top box refused to turn on, you opened it and, after ringing, found two or more terminals in a short circuit or low resistance? Such converters, due to the fact that their wiring is sometimes individual and incompatible with other types of converters, it is necessary to replace them strictly with exactly the same ones, or, in extreme cases, with complete analogues taken from the datasheets.
Converter chip pinout
The connection diagram, component ratings, output current, and, of course, the output voltage must completely match. I received one of these set-top boxes for repairs with the 3.3 volt converter power input punched to ground. A quick search in radio stores in our city showed that we have neither such a microcircuit nor complete analogues anywhere.
The fact is that for design on Arduino and microcontrollers, special small-sized boards of converters and stabilizers are produced in China, immediately with the necessary kit soldered on the board for their operation. These are AMS1117 stabilizer chips familiar to many electronics engineers.
AMS1117 stabilizer chips
These microcircuits are produced both adjustable, which in this case is unnecessary for us, and with a fixed output voltage, but we are interested in voltages of 1.2, 1.8, 3.3 volts. For all these voltages there are ready-made converter boards based on these stabilizers. How can you distinguish converter boards if, for example, you bought them earlier and forgot what voltage they were for?
On the case of the microcircuits, in addition to the model name, for stabilizers for a fixed voltage, the voltage that will be at the output of the converter is written, that is, the same 1.2, 1.8, 3.3 V we need. How to place these converters in the receiver case? They won’t take up much space, I wouldn’t think twice, I soldered the MGTF to three of the contacts on the converter board, there are 4 in total: input plus power, output plus power, and two contacts, a common ground for input and output.
I think it’s clear why we use three out of four contacts. How can we check ourselves whether we have found the correct pinout of the microcircuit, if the Chinese datasheet found, for example, raises doubts? Call the output indicated by the datasheet Vin, often if the set-top box comes with an external power supply, it is directly connected to the power socket. Also, between the ground and the power input, an electrolytic capacitor is often installed on the board, 220 uF x10 or 16 volts.
Capacitor 220 x 25 volts
The plus of the capacitor is connected to the power input of the converter microcircuit. What if you don’t know what output voltage this converter was for, that is, what voltage do you need to buy a converter for? You can try, after dismantling the burnt microcircuit and cleaning the contacts on the board from solder, apply power to the receiver and measure the supply voltage on the two remaining converters. And determine the voltage at the output of the remaining microcircuit by elimination. Solder this burnt-out converter using a soldering gun, or by applying a drop of solder, Rose or Wood alloy to all contacts, and warming them up quickly alternately with a 25-watt soldering iron.
If you are sure that the converter has burned out and are not afraid of burning it with the high temperature of the tip, during dismantling, you can apply a little ordinary POS-61 solder to all contacts and alternately heat the 40-watt terminals with a soldering iron, trying to move the microcircuit. If, after desoldering, it turns out that the short circuit was “underfoot” on the board, and not in the microcircuit, to finally make sure of this, you need to clean the contacts of the old soldered converter from solder using a dismantling braid, applying alcohol-rosin flux to the contacts with a brush (SKF).
Alcohol rosin flux SKF
Then we simply place the braid on top of the contacts and heat the terminals on top of the braid with a soldering iron. Our solder will transfer to the clean braid. For better absorption, the tip of the braid can even be dipped in alcohol-rosin flux. As the solder is absorbed, the tip of the braid should be cut off and the procedure repeated from the beginning. The same should be done with the contacts on the board remaining after the soldered converter.
Dismantling braid
There, as usual, we will be left with “snot” from the solder applied during dismantling - they must be removed. Then you can solder the MGTF wire connected to the contacts of the converter, finding from the datasheet for this microcircuit where we have the power input, where the output is, and where the ground is. It will be possible to check, as I wrote above, the contact connected to the ground by the power supply minus, we can call by touching either the polygon on the board, or if you are a beginner and are not sure of the correctness of the connection - the metal case of the USB connector.
Ethyl alcohol photo
After everything has been soldered, do not rush to connect the set-top box to the network, wash off traces of flux with alcohol, especially if you never know, you used a low-active flux, which in this case is a prerequisite for long-term operation of the device. Then look under a strong magnifying glass or take a photo with a phone with a good camera and make sure that you haven’t put “sniff” on the adjacent contacts, because they are located quite close to each other.
Multimeter in audio mode
To be completely sure that there is no short circuit, or if you couldn’t find a strong magnifying glass, test all adjacent contacts relative to each other for short circuits with a multimeter in audio testing mode. All these procedures with replacing the converter make sense only in one case - if, after checking the datasheet, you did not find a short circuit of the power input pins to the power output, since in this case your processor or RAM chip has already burned out due to the supply of an excessive supply voltage.
Which, of course, is sad, since then it will be impossible to repair it either at home, or even in a good workshop, due to the laboriousness of the repair and its high cost - higher than the cost of a new set-top box, it will not make sense.
Conclusion about the work done
Any more or less trained radio amateur can easily cope with this repair, and due to the low cost of the board for replacing the converter, it can be recommended as a means of albeit a “collective farm”, but very budget solution, in the event that a thrifty radio amateur does not have extra funds for buying a new console. Or you simply have a desire to prove to yourself that it is sometimes quite possible to carry out repairs of complex digital equipment on your own. Happy repairs everyone! AKV.
The fleet of analogue TVs is rather reluctant to give way to digital equipment, gradually taking “second” places - in the kitchen, in offices, garage workshops, etc. At the same time, DVB-T2 set-top boxes are also carried. We have already managed to evaluate the advantages of the latter; 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 the switching power supply - most cases of failure are associated precisely with a malfunction of the power supply, and a malfunction of the power supply can entail such serious consequences that repairing the device will be impossible. And yet, using the example of two digital TV set-top boxes, the possibility of repairing them independently will be considered here. The first device was TVK 3101. When turned on, the image had severe distortions and periodically disappeared completely. A few days later, the set-top box began to turn off a few seconds after the manufacturer's logo appeared on the screen.
The second device is the Oriel 740 set-top box. This device did not respond to commands from the remote control, the indicator barely glowed red.
After opening the console cases, it turned out that in both cases the electrolytic capacitors of the secondary power filters were swollen.
It should be borne in mind that when working with the set-top box, special care should be taken - the primary power supply rectifier converts an alternating voltage of 220 volts into a constant voltage of about 300 volts, and this potential remains at the terminals of high-voltage electrolytic capacitors for some time after the power is removed - up to several tens of seconds . In the pictures they are located between the pulse transformers and the plugs of the power cords. Before working with the device board, these capacitors must be short-circuited through a resistor with a resistance of 51-62 kOhm.
Both faulty capacitors turned out to be almost the same - 1000 µF, 10 V. The picture shows one of them. The fact that its lid looks barely deformed should not give you the slightest confidence in the serviceability of the part - even if some part of the container has been 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 higher one, as in the picture - instead of a 10-volt part, a 16-volt part is shown, and with the same dimensions. Of course, faulty parts should be replaced with new ones, not used ones - otherwise the repair will soon have to be repeated.
After replacement, we turn on the set-top box - the indicator lights up brightly, the device responds to remote control commands, the image is stable. But the renovation is not finished yet...
There are traces of flux on the board - solder paste, rosin... Through such a coating, high-frequency currents can quite easily pass wherever they want. As a result, over time we may get an unstable image, noise, etc. troubles. Therefore, carefully wash the board with a cotton swab moistened with alcohol or acetone. After such cleaning, wipe the board with a dry cotton swab.
We install the board in place, check - it works.
Now we assemble the console completely and check its functionality again.
We check the second device in the same way - the device is working normally, the repair is completed.
In conclusion, I will add that the quality of the antenna amplifier power supply also greatly affects the operation of the set-top box. Thus, if the capacity of the filter capacitor is insufficient, signal loss is possible - there have been cases of complete loss of channels of the second multiplex. To recognize a malfunction of the antenna power supply, it is enough to replace it with a DC source of 9-12 volts (for example, a Krona battery or a battery from a computer uninterruptible power supply). If the reception quality improves, you should replace the antenna power supply with a known good one.
Any normal person, to put it mildly, is not satisfied if the services he pays for work poorly. However, technical failures in equipment operation are inevitable. What to do if the Rostelecom set-top box does not work, typical faults that may arise, and ways to fix them yourself, we will look at in the article.
Problems with Rostelecom television
So, if there are problems with Rostelecom interactive television, it is necessary, first of all, to localize the problem. The lack of a TV signal can be caused by several reasons:
- problems on the provider side;
- problems with the router;
- cable damage;
- The attachment is broken.
Today we focus on the last item on the list. It is important to understand that the lion’s share of problems with the Rostelecom TV set-top box can be easily and quickly resolved on your own, without contacting the company’s technical support service. It’s worth starting, as in the famous joke, by checking whether the electricity in your house is turned off.
If the Rostelecom set-top box stops working unexpectedly, most likely the problems are related to technical work on network maintenance. Contact technical support for information about the time frame for restoring network functionality.
When will rebooting the Rostelecom set-top box come to the rescue?
Many faults can be eliminated using the classic method - a regular restart. When rebooting, the Rostelecom set-top box will check for the presence of an updated software version and, if available, download and update the device firmware. Many users do not disconnect the set-top box from the network for months, so software updates do not occur. To be on the safe side, it doesn’t hurt to reboot the router, as well as unplug the cable and reconnect it.
And yet, after disconnecting the router from the network, they first turn on the router, which normally takes about three minutes to load. Then turn on the console. The lights on it light up, but the console does not load instantly. You will have to wait 4-5 minutes.
This method usually helps if the Rostelecom set-top box freezes once. But the opposite option is also possible: after the upgrade, the Rostelecom set-top box begins to slow down, precisely because of the incorrectly installed update. In this case, try resetting the set-top box to factory settings. This can be done through the main menu of the device.
Some are craftsmen on their own. The prospect is tempting, as it allows you to turn an average device, tailored under Rostelecom, into a full-fledged media center. But the risks are also high - sometimes after the manipulations the device simply does not turn on. On the other hand, it is flashing that allows you to cope with most of the “glitches” of the device that cannot be eliminated in other ways. For those who are comfortable with technology, we recommend that you do not do this yourself, but contact technical support specialists.
Another common and easily solvable problem is incorrect connection of the LAN cable. If the connectors are mixed up during connection, the set-top box will not work.
Trivial problems with the Rostelecom prefix
Let's look at the most common problems with the set-top box that the user encounters and the actions he can take to restore functionality.
If the error message “Rostelecom set-top box cannot obtain an IP address” appears on your TV screen, there are most likely problems with accessing the Internet. The reason may be either on the provider's side - an accident or technical failure, or on the end-user's side - physical damage to the cable or incorrect operation of the router. Disconnect the router from the network for a few minutes and turn it on again. Did not help? Call .
If the Rostelecom TV set-top box does not respond to the remote control, simply try replacing the batteries. If it doesn’t help, configure the remote control yourself or take it to a service center.
To fully control the operation of the TV using the remote control from the set-top box, special settings are required. It is better if this is done personally by a Rostelecom technical specialist at the time the subscriber connects to the network.
Typical situation: only federal channels are shown, and the rest included in the Rostelecom package are not available. It is most likely that telecommunications services were not paid on time. Sometimes access is blocked by mistake. If you are sure that the payment went through, you may have accidentally blocked access to the channels. Call the operator's hotline to clarify the situation.
There are situations when the playback of video and audio signals slows down. The image disintegrates and the sound stutters. This is usually due to network congestion. Try disconnecting other home devices from the Internet, the problem should be resolved.
The main “devourers” of the channel are downloads from file hosting services. Understanding this, you can independently regulate the workload level.
If the picture is “normal”, but the sound on the Rostelecom set-top box disappears, there is apparently damage to the RCA cable. Try moving the connector. If the sound can be restored, the problem is localized. Replace the cable with a new one.
If the performed manipulations do not help, feel free to take the set-top box to the service center. Experts will determine whether the failures are caused by problems in the hardware or software. And most likely, your device will be replaced with a new one.
Of course, problems with Interactive TV may arise. But these inconveniences are more than compensated for by the range of opportunities that the new format provides. Don’t be afraid to contact technical support once again - this is the only 100% effective way to solve problems.
