Diagram of the power supply for a digital set-top box for a TV. The secret of creating Android smart TV set-top boxes - who needed it?

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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. Further diode bridge, an electrolytic capacitor after it, a PWM chip. 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 try to supply 5 volts with external source direct current, with an output current of at least 1.5 amperes per power supply capacitor. 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 chip, 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 can get unnecessary problems, and you 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 additional settings item: “Sleep timer”, or type: “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) decoder Dolby Digital(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 sound 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 in normal mode(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").

If your DVB-T2 digital set-top box for receiving terrestrial digital TV has stopped working, then in some cases you can solve the problem yourself. In this article we will describe the most common problems that arise when using digital set-top boxes. You will also be able to determine whether viewing problems are a defect in the set-top box itself or whether it is an issue with the antenna or TV.

The set-top box does not turn on

This is one of the most common digital failures. broadcast consoles. It manifests itself, as a rule, in two variants: the receiver shows no signs of life at all, or the red standby indicator is on, but the set-top box does not go into operating mode. Most receivers start working immediately after being plugged in and do not require turning on from the remote control. If this does not happen, then it is most likely that your power supply is faulty.

Power unit - weakness in any technology and digital set-top boxes are no exception. The power supply may fail completely - in this case, not a single indicator on the set-top box lights up at all and the device does not react in any way to being connected to a 220V network. But it often happens that the power supply produces too low voltage or current. In this case, the tuner “tries to turn on” by showing some signs of life, but does not go into operating mode.

Solution to the problem: If the power supply is external (as in the picture), then solve this problem easy and on your own. Power supplies for set-top boxes are usually standard and interchangeable even different models and manufacturers. You just need to make sure that the new power supply produces a voltage of 5V and has the same plug at the end of the wire as the old one. You can buy one in specialized stores that sell antenna equipment. In most cases, you can ask the seller to connect the power supply to your receiver and make sure that the problem is resolved.

It is more difficult if the power supply is built into the console. A characteristic feature indoor unit The power supply is a regular plug at the end of the wire. In this case, the power cord is not disconnected from the set-top box itself, as is the case with the external version. In this case, it is best to contact a service center for repairs.

The image freezes shortly after turning on the console

This defect is quite rare, but if it is detected, repairing the receiver is most often impractical. A clear sign of such a malfunction: the appearance of image distortion and “freezing” of the picture, which appears 5-20 minutes after switching on digital tuner , after which the problem does not disappear. Similar symptoms occur with weak signal from the antenna, but in the latter case, image distortion does not have a clear connection with the operating time of the DVB-T2 receiver.

The problem could be the same power supply or overheating of the processor. If the power supply is external, you can try connecting another power supply. If not, then the problem is in the processor itself and repairing the product in this case is impractical.

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 06.01.2017

 Denis Bolshekov

If you are wondering: Why does the digital set-top box not display or display poorly? You are at the right place.

Let's understand this situation.

Digital DVB-T2 television does not show and what to do about it?

First you need to make sure that you are in the zone confident reception DTV. If the set-top box used to show and then suddenly stopped, possible reason V incorrect connection antenna equipment. Or the DVB-T2 receiver is out of date, this can be solved by downloading new firmware from the manufacturer's website.

We will assume that the console is in full working order. In this article we will configure only the set-top box itself and the antenna.

Problem: not all channels were scanned and caught

You did an auto search and your set-top box did not find all channels - you need to manual search channels. Most likely, the set-top box did not receive the signal from the second multiplex, and you will need the frequencies of the nearest transmitting tower.

If the TV shows nothing at all

You selected the wrong video input or did not switch the TV to AV or HDMI mode. Or they simply didn’t turn on the set-top box; it should have an indicator that lights up green when turned on. The set-top box is turned on either with a button on it or with the remote control.

The set-top box is turned on, but the TV says "No signal"

If this happens, most likely the antenna is turned off, or its amplifier is not turned on. Check if the antenna is connected, maybe it has come loose, pull it out and put it back in. Repeat auto search.

The set-top box says "No services" auto search found nothing

If the channels stop showing and the set-top box says “No services”, then the problem is bad signal. You need to repeat the search in manual mode. The fact is that with a weak signal, auto search can skip channels. On the contrary, a manual search by frequency will show the strength of the signal, even a very weak one.

Picture with friezes squares

We need to look at the signal level. Press INFO on the remote. Same behavior as Katrinka digital set-top box observed if you are far from the tower, or large buildings interfere with signal reception.

The solution here is that it is necessary to amplify the signal using active antenna, or put the antenna outside, raise it higher, and the like.

If the signal and picture quality is poor, we adjust the antenna

If the signal intensity is high but the picture quality is poor, then you need to either replace or try to adjust the antenna. Literally turn the antenna in different sides. The mustache is responsible for the meter range, and the ring for the decimeter range. Here we turn the ring in different directions. It is advisable to move around the room or place an antenna on the windowsill.

Digital television works great with a reflected signal. But it is very sensitive to obstacles from reinforced concrete walls and plastic window frames.

As a result we get

If you need to understand why it doesn't work digital television? If the signal is weak, then it must be amplified using an amplifier or an active antenna. Find in the room optimal location antenna, “turn” it.

Since the late 90s of the last century, audio-video technology has evolved greatly. From VCRs and DVD players, CD and MP3 tape recorders, to omnivorous media players that allowed you to read media files from USB flash drives. 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 from digital quality, albeit 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 do-it-yourself repair consoles, instead of them they install stabilizers with 3 legs, replacement is not difficult, but sometimes boards have unreliable five-legged converters, 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 as adjustable ones, which we need in this case unnecessarily, and with a fixed output voltage, 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 high temperature tips, when dismantling, you can apply a little ordinary POS-61 solder to all contacts and alternately heat the 40-watt leads 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 chip 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 plug in the set-top box, wash off traces of flux with alcohol, especially if you never know, you used a low-active flux, which in this case is prerequisite long work devices. 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 “snot” 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 involving replacing the converter make sense only in one case - if, after checking the datasheet, you did not find short circuit 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 too high 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 labor-intensive nature 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 handle this repair, and due to the low cost of the board for replacing the converter, it can be recommended as a tool, albeit a “collective farm” one, but very budget decision, in the event that a thrifty radio amateur does not have extra funds to purchase new console. Or you just want to prove to yourself that repairs are complicated digital technology Sometimes it’s quite possible to do it on your own. Happy repairs everyone! AKV.

If the search results in only 10 digital channels instead of the desired 20, then first of all you should make sure that viewing all channels in your location is in principle possible. This can be done by using, interviewing neighbors, or calling specialized organizations involved in installing antenna equipment. You should not call Eldorado or Auchan, since in most cases they do not have such information. Call a company that specializes in installing antennas. As a rule, these are companies that install, among other things, satellite dishes and you can find their coordinates, for example, on the website tricolor.tv in the “Where to buy” section. If reception of all 20 channels is possible in your area, check the antenna and cable.

Channels freeze or signal disappears

For stable operation of digital television, it is important that the received signal is of sufficient level. More precisely, it is important good value signal/noise When this ratio falls below certain limit, problems with viewing begin. The easiest way to see the signal level is to double-press the INFO button on the problem channel on the remote control of the DVB-T2 set-top box. A “quality” scale should appear on the screen and its value should be as high as 50%. Often, next to the signal scale, a “level” or “strength” scale is displayed - there is no need to focus on it. If the signal level is low, then the advice is still the same: check the cables and antenna and, if necessary, replace it.