Electrical circuits of digital set-top boxes dvb t2 reflect. Rostelecom TV set-top box does not work, troubleshooting possible problems
The fact that digital television provides an image on the screen best quality, how analog signal, many of our compatriots have already been able to verify.
In order for your home to be able to receive digital channels, you need:
- 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 malfunctions in the operation of equipment forced the broadcast to be suspended and repairs began 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
In the event that the signal is received at weak antenna without amplifier or with low power amplifier, or there are high-rise buildings or other noise-producing structures in the space between the antenna and the television 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 more powerful antenna or moving the existing antenna to the highest possible height to ensure direct visibility of the tower.
This is easy to do if you mount the antenna on 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. 
Download required version You can download the firmware from the receiver manufacturer’s website, but it’s not so easy to do it 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 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. Get acquainted with one of standard schemes converter can be seen in 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 neither such a microcircuit nor complete analogues We don't have it 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 leads 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 plug in the set-top box, wash off traces of flux with alcohol, especially if you never know, you used a weak 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 cope with 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 case of absence extra funds from a thrifty radio amateur to purchase 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 most common malfunction of set-top boxes digital television is a failure of the power supply. In such an unpleasant case, it is very good if the model of the console had an external adapter, buy a new one and look further! And if not! And was the power supply built into the console itself? Then you will have to repair or purchase a new one. But perhaps there is an easy way out!
Hello, dear readers! In this article I want to share one way simple repair, which can be carried out by anyone who knows how to hold a screwdriver and a soldering iron in their hands! Moreover, it is not necessary to master these instruments masterfully.
I’m also not going to tell you anything overly complicated in the field of electronics repair, this is the domain of professionals. On the contrary, I will try to describe everything in such a way that even a non-specialist could cope and eliminate this malfunction.
I’ll immediately make a reservation that this method is not suitable for all models of consoles, but for many, since they are often made according to a very similar scheme for this case. Everything will be on specific example set-top boxes from the D-Color company, namely the DC1401HD model. So having understood this “ high technology» you can repair your digital television set-top box yourself.
Quick navigation through the article
DIY console repair
What is a sign that the power supply in the set-top box has failed, and not something else? If the set-top box connected to the outlet does not show any signs of life, neither the digital indicator nor the LED on the front panel lights up, then with a 99% probability the reason is in it, in the power supply.
If at the same time the warranty period has already expired, then you can safely start disassembling it. As experienced craftsmen say, “An autopsy will show.” I think you can figure out this part of the work without detailed description, just be careful, usually there are two screws on the back wall, sometimes also on the sides, allowing you to release and open the top cover. Plastic latches on the sides and bottom hold the front panel, and the board itself is also secured with screws to the bottom of the case and in the area of the connectors on the rear wall of the case.
So, the console is disassembled, power cord also removed from the connector, it will no longer be needed. On the bottom of the case there are traces of a “fire” left behind by a burnt-out power supply.
P.S. The power supply here is not a separate unit, as you might think from the name, but a section of the board on which radio elements are located that provide the required supply voltage to the set-top box.
What is the modification?
I'll outline big picture, and for those who already have a little knowledge of radio engineering, this will already be enough to grasp the basis of the idea and repeat it. So, the power circuits of this set-top box produce only one voltage - 5 Volts. Since this circuit has burned out and repairs may not be practical (given the total cost of radio components and repairs), there is a simple solution. Replace internal source power to external. It's not very difficult!
In the photo above, a yellow frame highlights the area of the power supply that has failed. The board has already been washed so no traces of burning are visible. By the way - Among repairmen, the expression “Burned out” does not always mean literal combustion with charring and other similar manifestations, it only means that the radio components have failed.
For our repair, you will need to purchase an external power supply with an output voltage of 5 Volts and capable of delivering a current of 1.5 or better than 2 Amps. Nowadays there are a lot of similar ones that can be purchased inexpensively, or maybe you have something similar, for example, an unused charger from a tablet or smartphone.
When a suitable adapter is available, all you have to do is find it desired point on the set-top box board and, observing the polarity, apply voltage to it from external unit nutrition. All! All that remains is to lay and secure the wire, or you can organize a detachable connection, as you like. I think the basics are clear, let's move on to the details.
A short introduction to the power supply circuit of the set-top box
Just a little background for those who are not in the know so that you can figure it out. Pay attention to the photo. Click to enlarge.
In short, the power supply consists of:
- The primary “Hot” part - It is called Hot because it is dangerous, connected to the mains voltage of 220 volts. Please note that even after unplugging it from the socket, for some time, there is still a charge there that can bring brr.. 😯 unpleasant sensations if you climb into it. But in our case, there is no need to go there and we won’t plug it into the outlet either.
- Secondary part - It is safe there, there is galvanic isolation from the electrical network. In the above example, at the points indicated in the photo, with rectifier diode The output voltage is only 5 volts.
Let's get down to business
In the purchased external power supply (at least 1.5 amperes, 5 Volts), we bite off the plug, strip the ends of the wires and, having determined the polarity, solder them: The positive one to the diode terminal, on the side where the stripe is drawn on it, and the negative one to the common bus - frame USB port will be a convenient place for this. If you don’t know how to determine polarity, even without a device, see additional materials at the end of the article.
Connecting new block power supply to the network, take it out of standby mode, check what happened.
Everything is OK! All that remains is to lay and secure the wire so as not to accidentally pull it out, collect everything in a pile and use it. In the end it will look like this.
If you need ideas on how to secure the wire to the console body? How to determine polarity without a device? Or how to solder a wire from the bottom side of the board? — These additional materials are located further in the text.
Probably, every person has encountered the failure of one or another equipment, and in lately The actual situation is when digital television does not work. A person turns on the TV to watch a long-awaited continuation of a series or a favorite show, but only gets a blank screen. But digital television does not work every time for some reason that no one understands. Either there is no broadcast, or the signal does not pass through, or prevention is carried out on separate channels. Digital television also does not work if the antenna or even the TV itself breaks down, or maybe the cable comes loose somewhere. There are many, many reasons why there is no television broadcasting. This article will help you understand some of them.
Main reasons
If digital television does not work due to lack of signal, it will be immediately clear, because not a single channel will respond. This means something happened to the antenna. Prevention cannot take place on all channels at once, most often on just one or, in extreme cases, on several. The rest will work, and why digital television does not work is not a question for such a situation. If a cable has come loose somewhere, then the question is legitimate, because silence and dark screen will be everywhere.
The first thing you can check is that everyone knows, even people far from technology. You need to disconnect and reconnect the cable. If it doesn’t help, then contact specialists and ask them why digital television doesn’t work today. If the user suspects the reason is that the TV is broken, there is no point in independent actions No. It will only help service center or a private master who knows how to repair TVs.
Much, much if
Users cable television have the opportunity to immediately contact the company that provides broadcasting services as soon as they discover the absence of sound and video. There are usually experts there, they will always help in all cases. If there is no cable television, then first you need to get to know your neighbors and ask if everything is okay with them.
If their digital television has not stopped working, then all problems should be looked for at a specific user. If using a regular indoor antenna, problems usually arise frequently, so many people now purchase special amplifiers, then there is no answer to why digital television does not work. An antenna amplifier is a very effective aid, and it is not difficult to purchase - it is not too expensive and is sold everywhere, in every household appliance store.
Common problems
Satellite television antennas are very powerful, but even they sometimes refuse to transmit a signal, and a frustrated user spends a lot of time with the phone in his hands, asking the broadcasting company why digital television is not working today. This problem is considered common. The satellite is moving, and it was to it that the antenna was tuned, and it was from it that it caught the signal.
It exists, but is not available. The problem can be solved quite simply, but not every user can independently reconfigure the antenna to another satellite, so it is better to immediately contact specialists. Moreover, it is not a fact that the satellite has moved. The antenna may also change its position due to the wind or because an object, such as a tree branch, falls on it.
About the benefits and harms of curiosity
There are many reasons, and users have even more solutions, unless, of course, they cannot correctly determine the reason why digital television is not working well. If the cause is unclear or the user made a mistake in the diagnosis, additional problems may arise when acting independently. Therefore, it is better to resort to the help of real professionals. They will determine why 20 digital television channels do not work, or, for example, only ten out of twenty work.
Not too knowledgeable modern technology the user is unlikely to be able to do this. But there are (and quite large quantities) people are inquisitive, and it is their choice: to establish a signal or to break something else. You can only eliminate some minor defects on your own, and those that are visible, for example, placing the cable correctly in the socket or choosing an amplifier for the antenna in a store. The rest needs to be left to specialists.
Far and near
In the city it is much easier to get answers to the following questions: why digital television channels do not work, why there is poor sound and image reception, why not all channels work well, and many more questions regarding broadcasting and reception. But very often there are situations when it is difficult to solve such problems even in a metropolis. It is impossible to even list all the cases in which even a master cannot immediately cope if digital television does not work.
Kaluga, for example, is a very modern city, but for some reason there are a lot of reviews on the Internet about signal problems from there. City residents generally have much less problems calling technical support, but how much more difficult it is to resolve issues of this nature far from civilization! In the outback, time does not flow so quickly; modern technologies arrive there very late or never arrive at all. Therefore, fans of digital television need to find out what options exist for them today.
Three options
Firstly, this is cable television, when the signal will be distributed directly through tv cable, and it connects to a separate TV. This is a very high-quality transmission, but it is not available in every outback, mainly in cities. And the subscription fee is quite high.
Secondly, this is satellite television, when the signal comes from low-Earth orbit and is received by an individual antenna (“dish”). This can be done everywhere, and the sound and picture will be of high quality. The subscription fee is quite high, and the equipment is also expensive. And from time to time, the user still asks the question: why did digital television stop working?
Thirdly, terrestrial, when the signal is distributed by ground-based repeater stations and is received by an individual antenna. There are few costs here, but the signal level is much lower, the quality of reception depends on everything in the world - here is the weather, and the distance from the relay tower, and the height of the antenna mast, and much, much more. And every user will be in a bad mood from time to time due to the fact that terrestrial digital television does not work.
Of course, nowadays the Internet helps everyone everywhere, where you can always watch whatever you want. However, this article is not about these cases.
Theory
All these methods are quite good. But when choosing one of them, it is necessary to imagine at least in general terms how they differ. For example, just terrestrial television and digital are completely different. The latter is that digital coding is used to transmit image and sound - both the audio signal and the video signal. And for transmission they are used digital channels. This coding provides minimal losses when delivering a signal, since no interference with the encoded information is dangerous. And if digital television channels do not work, then they do not work completely, at all. And if they work, then only in excellent quality. There is no borderline state or interference here. An exception is only what happens bad quality communications. Then the TV seems to slow down, turn off and turn on again. And this can only be corrected in one way - you need another antenna or the existing one needs to be raised higher and turned towards the TV tower.
It should also be noted that many users do not know that digital television is always limited in the number of available channels. Depending on the region there may be ten, twenty, the number varies. The principle does not work here: raise the antenna higher and catch absolutely everything. No, only what is available can be configured. For good viewing First of all, you need to purchase TV antenna, TV or television with support for signal compression standards and a tuner (you need to find out which one is on at the moment not yet outdated). To many most modern TVs They don't need a set-top box, they just need an antenna. But not everyone has these, and therefore users often look for the reason why the digital television set-top box does not work, although the problem may be in the TV itself.
Practice
Let's say you have chosen terrestrial digital television for use. You can use the most regular antenna, which catches two or three channels well in fairly good quality, a couple more in poor quality, but even those in very good weather. This antenna requires an attachment. For example, DVB-T2. Any one is possible, they are technically almost identical. Most often, set-top boxes have two outputs - SCART or “tulip” and HDMI output, as well as a USB connector to view content electronic media. The boxes for all consoles are different, but they seem to be made at the same factory in China. Therefore, when purchasing, you need to carefully inspect the control panel, as the most frequently used item, to see if everything is in order with it. Otherwise, there will be problems in switching channels, adjusting the volume, and the like. If all is well, you can connect the antenna to the set-top box, and the set-top box using a “tulip” (usually sold in one set with the set-top box) needs to be connected directly to the TV.
Here you need to know that RCA connectors for stereophonic sound and video signal - this is the same “tulip”. Yellow is for video, white is for left stereo or mono, and red is for right stereo. If the TV picture tube is obsolete, the “tulip” will help out. If the TV is plasma or LCD, it has an HDMI output, and you need an appropriate cable, another will not work. You need to purchase it separately. Otherwise, the user will not like the image too much. The TV needs to be switched to AV mode, then the set-top box interface will appear. Setting up the console is not too complicated. Even if you just do everything by default, the quality will completely satisfy even connoisseurs. The main thing here is to configure the channels themselves. The menu has a channel search. You can also select auto search. In a few minutes everything will be ready. This will be enough for almost any settlement.
From electronic media
As already mentioned, it is needed in order to play back what was recorded on a flash drive. To do this, you need to insert USB device into the set-top box, go to the menu, select "USB" "Multimedia" accordingly, then select required format- videos, pictures or music. The contents of the flash drive will open on the screen. Now you need to choose the desired folder and open the file. Everything is even simpler than doing this with a laptop or computer. However, many people still cannot figure out these operations on their own. Especially for older people who can’t keep up with fast-moving traffic. technical progress, we need help. Young people cope best with this. And even small children are much more adaptable.
But that's not all. A user who has such an antenna attachment for digital television should know that it is possible to perform the reverse operation. For example, record your favorite program directly from the TV onto a flash drive. And the steps for this purpose are just as simple. Just press the “Rec” button on the control panel of the set-top box, and the recording will obediently go to the USB device. In a word, digital television today, even for a remote locality, is not a myth or a dream, but a completely feasible thing. And if it is digital terrestrial, then a resident of the outback or temporarily settled in a country house or village does not necessarily have to spend about ten thousand rubles on installation satellite television, and then contribute a considerable subscription fee. You can still achieve comfort today with small means.
Trust the provider
Almost everyone enters into an agreement with a provider in order to receive digital television services. Long-running and fairly powerful companies supply a set of equipment to the user, such as, for example, Rostelecom. However, almost all providers do not satisfy the client on the day of contact. You have to wait a day or two, and if this is the outback, then a week, not even one. In order not to waste time, and digital television to work immediately, you can make initial setup on one's own. This knowledge and skill can be needed by literally everyone, even if you have to move the TV to another room or exchange it for a new one you just bought. Therefore, everyone should understand connection diagrams and configuration technologies.
The same Rostelecom offers this service in two versions - together with the Internet (“Interactive 2.0”) and separate digital television (“Interactive TV”). The latter can only work on a router that belongs to the company; others will not work. And Rostelecom’s routers are disgusting, that’s what all the reviews say. Therefore, it is better to choose 2.0, and if there is no other provider nearby, you will have to call technical support almost every day with the question: why does digital television not work during the day? You won’t be able to connect version 2.0 yourself; you’ll still have to wait for technicians. Rostelecom's settings do not match other people's equipment. The user is lucky if another provider is nearby and can connect him to their network.
Situations
1. The set-top box leaves the normal mode. This can happen if it is turned off for a long time. You just need to plug it into the network and not be afraid of the inscription that says that the channel is DRE encrypted. If you wait a couple of hours, the operation of the receiver will be fully restored and all encrypted channels will open.
2. It may happen that the set-top box (receiver) is not registered. To eliminate this situation, you need to look at the identification number on the back panel and enter it on the provider’s website.
3. Sometimes the antenna settings get lost. Such cases are described above. Here you will need the help of a specialist who will reactivate them.
4. If a sign suddenly appears on the screen paid channel, you just need to pay for a subscription to the provider’s services, apparently the user forgot to do it on time.
5. Sometimes there are compatibility difficulties software. This will require some dexterity. If the receiver is GS-HD, you need to restore the channel list in the menu (there is such a key there). And if that doesn’t work, you need to press two buttons on the remote control and on the receiver panel at the same time (this is the most important thing) - CHANNEL and TV/RADIO. Exactly at the same time - with four fingers. And then press STANDBY on the remote control. And everything has to fit together in the software.
6. If “No Signal” appears on the screen, you should look for a solution to the problem with the antenna. This has been discussed a lot above.
7. Check the cable. If it doesn't help, call a specialist.
In the article, the author shares his experience of repairing a tuner for receiving terrestrial digital television programs. The troubleshooting technique he described is applicable to other electronic products, where one or more functional units are powered by a voltage stabilizer with unknown output parameters.
The "Globo GL50" tuner is designed for receiving DVB-T/T2 terrestrial digital television programs, as well as for playing multimedia files from external media, connected to the USB port of this set-top box. After working for about a year, this tuner broke. The malfunction looked like a complete inoperability of the device, while the LED on the front panel glowed yellow. Repairing such devices is usually impractical, but since in modern digital devices ah, there are few interesting parts for future use, it was decided not to disassemble the receiver into parts, but to try to repair it.
The troubleshooting began by checking the functionality of an external power supply with a stabilized output voltage of about 5.2 V at a load current of up to 1.5 A, which turned out to be serviceable. Next, the integrated voltage stabilizers were tested on the block board (its marking is M3103-0C). At the output of one of them (KV3VC - according to the U4 microcircuit circuit) there was a voltage of 0.537 V, while the microcircuit body was heated to a temperature above 100 o C in five minutes. This stabilizer directly powers the tuner's central processor, which remains cold. The initial version that one of the ceramic blocking capacitors C23, C24, C35 was broken was not confirmed.
Disabling the stabilizer load did not change the situation: the chip body also became very hot. Because no useful information Neither the failed microcircuit nor the board itself could be found; we had to find out what voltage was required for operation central processor experimentally. To do this, the U4 chip was soldered out of the board, and the output of a powerful laboratory adjustable block nutrition. At a voltage of 1.1 V or less, the tuner processor worked with errors or froze. At a voltage of 1.2 V, the processor worked without errors in all operating modes of the set-top box, consuming a current of about 0.6 A.
Because even if it were possible to find and purchase the same microcircuit to replace the failed one, its installation, in the author’s opinion, is devoid of practical meaning (what burned out once will burn out a second and a third time); It is not enough to simply eliminate the malfunction; you need to eliminate the causes of its occurrence. Probably, the KV3VC integrated stabilizer burned out from overheating - a typical malfunction of modern digital devices, it ranks first in the number of failures of devices for household and industrial use (in second place is printed wiring, and together they “take away” more than 90% of all malfunctions that did not arise due to improper use).
It was decided to replace the faulty switching stabilizer chip with a linear stabilizer with an output voltage of 1.3 V on the KR142EN12A chip, the circuit of which is shown in Fig. 1 (positional designations of its parts begin with the prefix 1). The output voltage is set by resistors 1R1, 1R2. The lower the resistance of the first of them (with the second remaining unchanged), the lower the output voltage. Capacitors 1C1, 1C2 are blocking. Diodes 1VD1 - 1VD3 protect the load from damage if 1DA1 malfunctions. Taking into account the voltage drop on the connecting wire, the output voltage of the stabilizer was approximately 1.28 V.
Rice. 1. Stabilizer circuit
The parts of the new voltage stabilizer are placed on a circuit board measuring 22x22 mm. The KR142EN12A microcircuit is installed on a ribbed duralumin heat sink, which is tightly pressed to the bottom and side walls of the metal case of the set-top box. Since the heat sink flange of the microcircuit is electrically connected to pin 2, it is fixed to the heat sink through an insulating gasket; a PVC tube and a getina washer are put on the mounting screw for insulation. All mating planes are lubricated with heat-conducting paste. Instead of KR142EN12A, you can install KR142EN12B or one of the imported ***317 series in the TO-220 housing (for example, LM317, KA317). The purpose of the pins of all these microcircuits is the same. A view of the installation of the stabilizer and the “stuffing” of the attachment is shown in Fig. 2.
Rice. 2. View of the installation of the stabilizer and the “stuffing” of the console
The stabilizer input is connected to fuse link F1 (Fig. 3, red wire), the output is connected to inductor L4 (Fig. 4, green wire), and the common wire is to the negative plate of capacitor C35 (Fig. 4). Instead of 1N4001 diodes, you can use any of KD208, KD243, KD247, 1 N4002-1 N4007.
Rice. 3. Circuit board
Rice. 4. Circuit board
The M3103-0C circuit board can be used in other models of DVB-T2 receivers. Since the author has never come across “cold” DVB-T2 set-top boxes (they all get very hot during operation), after finishing warranty period It is advisable to measure and record the input and output voltage values of the stabilizers installed on the board, as well as photograph the circuit board on both sides so that all the inscriptions are visible; this can be useful when repairing a failed device. Keep in mind that several operating voltages can be generated simultaneously at the output of a pulsed integrated stabilizer. To improve cooling, you can install a small “laptop” fan inside the console.
After repair, the current consumed by the tuner from the power supply was about 0.75 A, which means that the external complete pulse block power supply with the output parameters specified at the beginning of the article is capable of providing power not only to the DVB-T2 set-top box, but also to the external device connected to it hard drive form factor 2.5 inches. If the set-top box is equipped with a power supply built into its case, to reduce the load on it and, accordingly, to reduce the temperature inside the case hard drives 2.5"" is preferably powered from an external unit.
Publication date: 20.01.2016
Readers' opinions
- Genn / 11/12/2017 - 07:30
Well told - thank you - admin / 10/31/2017 - 10:17
Unfortunately, there is no diagram! - ALEXANDER / 10.30.2017 - 19:00
Globo GL50 diagram where to find - Victor / 03/19/2017 - 11:47
Thank you! Interesting. Educational. - Vladimir Vasilievich / 29.12.2016 - 13:59
I’m 69. And I’m still interested. I liked the site and the sections. Since I’m still doing repair work. since 1967.Thank you 73. - Guest / 02/07/2016 - 20:23
The article will be useful to a certain circle of people, I liked it.