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 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 with an ESR 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 they burn out in receivers DC-DC converters. 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 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 housing 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 housing? 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 console comes with external unit 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 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 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 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 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 purchase new console. Or you simply have a desire to prove to yourself that sometimes it is 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 pulse block power supply - most cases of failures are associated precisely with a malfunction of the power supply, and a malfunction of the power supply can lead to 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 distortion 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 AC voltage 220 volts to a constant value 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 power supply antenna amplifier also greatly affects the operation of the console. 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.
Since diagrams for them are not freely available and apparently will not be, manufacturing plants respond with silence or unsubscribe about certified centers that are licensed to repair a particular brand. 1. THE RECEIVER DOES NOT TURN ON; The LED blinks or dimly lights, or does not light up at all - Apply 5 volts with external source(with an output current of at least 1.5 amperes) to the output capacitor of the power supply unit, observing the polarity, we see whether the receiver starts, if so, then we repair the power supply unit. Most often the output capacitor of the power supply requires replacement, we install a new 1000 uF 16 V, although more often they cost 1000 uF 10 V 2. There is 5 volts, the receiver does not start - we check the secondary power converters (five legs with inductors nearby), we measure on inductances 3.3 1 ,8 1.15 volts, if it is missing, we change the microcircuit. Information on “five-legged” devices can be found on sites such as monitor, etc. 3. If there is voltage on all stabilizers, as well as in cases where the inscription ASH appears, cyclic reboots, freezes during loading, etc. P. (the firmware has crashed) - we flash the flash memory chip 25Q32 4. DOESN'T CATCH CHANNELS - reset the settings to factory settings, search again, change the quartz resonator in the tuner (if available), after first making sure that the antenna is working properly. If it doesn’t help, most likely the problem is in the tuner, demodulator or processor chip, repair is impractical, especially for non-professionals, it will be scrapped... DO NOT HURRY TO CHANGE THE FIRSTWARE, in this case you can end up with unnecessary problems on your own head, without experience this often leads to a programmer . 5. NO COLOR AT ANALOG OUTPUT - change the quartz near the processor. 6. The image jumps and twitches, the color is distorted - change the capacitor located at back wall near analog outputs. 7. There is no signal through the analog output, but there is a signal through hdmi, the cord is fine, the socket is also fine - most often due to burnout of the outputs analog signals from the processor in the absence of buffer protective elements of the circuit. if there are buffer elements (usually installed via sound channels), check their serviceability. If there are none, then either viewing via HDMI, or scrap, well, or replacing the processor... Do not connect the set-top box to the TV while it is on! 8. The receiver turns off by itself - look in the menu in additional settings the item responsible for the sleep timer, or shutdown during inactivity, can be called differently! 9. When you try to update the firmware over the air, the receiver freezes - leave it on for half an hour, the receiver, not finding the update, will reboot and continue working as usual. 10. The receiver reboots when trying to search for channels or install a USB drive into it - most likely, the problem is in the secondary converters “five-legged” and the quality of their wiring, a good voltmeter and oscilloscope is desirable.
Repair manual for digital TV set-top boxes Reflect Digaital
Capacitors:
1 – Problems with the image on the AV output (no image, noise in the picture), sound clicking.
8 – Does not start – hangs on boot; the splash screen appears, and then again blue screen. In this case, the capacitance, when measured, can correspond to the nominal value (low ESR of the capacitor).
9 – Doesn’t turn on – no image at all
13 – seems to slow down too
14 – the picture slows down, the image blurs.
15 is the same as 14, but 14 is more important.
“does not pick up channels” - quartz between C13 – C15
Capacitors in the power supply: 
These two capacities affect the performance of the power supply. The power supply either does not work at all (output voltage 0V) or produces a low voltage of 1.7V.
Container 2 swells - you can see the insides coming out from below.
Voltage measurements: 
1. PSU output – 5V
2. Output AMS1117 – 1.8 V, if there is no such value – go to point 3
3. There should be 3.3V, if not, then the problem is in the capacitor nearby or in the AS11D itself
4. There should be 1.34 V here, but even if there is that much, the problem is still most likely in the capacitor - it’s better to change it. In this case, nodes 2 and 3 show normal voltage values. This is the case when the receiver starts to load and cannot completely do it - the problem is in the capacitor of node 4. We cannot exclude AS11D in this node, but the probability of its malfunction is very small, compared to the probability of a bad capacitance.
THE BIGGEST NUMBER OF PROBLEMS ARE CONNECTED WITH TANK 8 AND 9 (SEE 1 PHOTO) IF THEY ARE NOT EVEN THE PROBLEM, THEN WE CHANGE THEM AS A PREVENTION.
What to do if the digital set-top box does not work?
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 failures of digital broadcast set-top boxes. 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.
The power supply is a weak point 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 it’s easy to solve this problem yourself. 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 The internal 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 turning on the digital tuner, after which the problem does not disappear. Similar symptoms also occur when the signal from the antenna is weak, 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.