During operation satellite receivers Globo, Bigsat, Allsat, Yumatu, Lumax, Digital, Boston and others like them, one malfunction inherent in all of them was noticed:
The tuner does not start, the LED on the front panel is on, and the digital display does not light up or flickers weakly. The reason for this behavior of the tuners was a malfunction of the power supplies in the + 3.3V circuits, much less often in the + 5V circuits.
More than 90% were caused by poor quality capacitors (C15) of the power supply in 3.3 volt circuits.
It is important to remember that the stabilization of the voltage group of the entire power supply is carried out precisely along the + 3.3V circuit, and it is in it that the optocoupler LED (PC817) is installed.
Faulty capacitors often swell, and their end surface takes on a spherical shape. You can visually identify a swollen capacitor.
At the initial stage of the capacitor drying (C15), the voltage of +3.3V is normal (the feedback is still able to compensate for the decrease in the capacitance of the capacitor), (but the remaining voltages will be above normal). The voltages in the +5V, +12V and +22V circuits (in case of malfunctions in the +3.3V circuit) will be overestimated.(The stabilization circuit seeks to keep the voltage in the +3.3V circuit normal, while simultaneously increasing the voltage in all secondary voltage circuits)
After replacing the faulty elements, all voltages return to normal both at idle and under load.
voltage to diode D8 
voltage after diode D8 
voltage on the winding of the tr-ra
On the oscillogram "voltage after diode D8" (there should be a straight horizontal line at +3.3 V);
Replacing faulty capacitances is usually sufficient to restore tuner performance. Motherboards of this type of equipment have a fairly high reliability.
Note: Once, in addition to replacing the capacitors, it was necessary to replace the rectifier diode (D8) in the +3.3 V circuit. In some tuner models, the power supply circuit has a different numbering of elements.
In some cases, due to overvoltage in the network, 2 diodes in the bridge on the high-voltage side and a fuse burned out. Diodes burn out in pairs. Burnt diodes are short-circuited, so they only pull a fuse with them, the rest of the circuit usually remains intact.
Part of the stabilization circuit located on the low voltage side of the UPS.
Consider some of the nuances of the repair in more detail. If the receiver works, but not correctly, then at the beginning of the repair, first of all, you should check (or reinstall again) all the necessary software settings for the equipment. If this does not help, we proceed to check the antenna-feeder path - we check the antenna settings (if it has moved, if there are any damages or deformations). Next, check the converter and the supply cable.
The converter can be checked using Satfinder or another receiver - if there is a problem in it, then you will have to spend money on buying a new one (although some, especially inquisitive do-it-yourselfers, manage to cut the inner silumin case of the converter and get to its insides). I especially want to focus on when choosing an antenna cable - the use of a low-quality (China or Poland) antenna cable of the RG-6U type can lead to very serious consequences.
This cable does not stand up to criticism - the outer insulation can be torn off by hand, a violation of the insulation at least in one place leads to the fact that the inner sheath of the cable is filled with water! The use of bimetal as the material of the central core leads to corrosion in the first season. As a result of external factors, the cable may fail in a week (there have been cases!) After installation. Professionals in the field of satellite reception will advise you to use a cable from the Italian company Cavel, which is an order of magnitude more expensive than a proven cable from domestic manufacturers, which is also suitable for use.
Checking the integrity of the cable is not difficult if you have a multimeter. So, we checked all the external elements of the satellite system. If everything is in order, then you can safely proceed to the main thing - repairing the receiver. First of all, it should be mentioned that the incorrect operation of the satellite receiver may occur due to a “rally” of the firmware (rarely, but it happens) or its incorrect operation. In this case, flashing the receiver with new software can help us. To do this, we need a null modem cable, a bootloader, and the actual software itself. We talked about how to make a null modem cable in the chapter on. Loading the software into the receiver is an individual procedure for each individual model, and we will not focus on this. Another software malfunction of the receiving equipment may be a software failure during firmware or incorrect firmware. In this case, the receiver does not respond at all to any external settings. This happens due to the impact on the internal memory of the receiver's bootloader, or its erasure (for example, erase or incorrectly set the BIOS settings of your computer and see what happens). Resuscitation of such a "dead" patient is performed by using JTAG - a specialized protocol for programming and internal debugging of the receiver's resources using a specialized JTAG programmer. It is worth mentioning that this procedure is the lot of either professionals or fairly advanced users - there is a risk (if it works incorrectly) to completely ruin it. Next, let's start discussing the physical faults of the receivers.
The most common receiver failure is a power supply failure, as the most unreliable part of any electronic equipment. The power supply generates voltages to power the receiver's internal circuitry as well as to power the external LNBs and the motor drive (if installed). We start repairing the PSU by checking the fuses and protective breaking resistors. The burnout of these parts does not necessarily indicate a malfunction of the circuit - it may have happened as a result of a surge in the AC mains, or these parts originally had a manufacturing defect. If it was not possible to eliminate the malfunction, we begin to "dig" further. To do this, consider the principle of operation of a pulsed power supply unit on a block diagram.
In the UPS, the AC input voltage is first rectified, then it is supplied to power the controller and the converter, with the help of which the DC voltage is converted into rectangular pulses with a given (increased) frequency and duty cycle, supplied to the transformer. One of the output windings (UN) is used for control - depending on the voltage in it, the PWM controller changes the frequency and duty cycle of the pulses in the high-voltage winding (HV). This maintains a stable output voltage. The UPS has another type of parameter control (KN) - voltage control to power the digital part of the receiver - the processor and memory. The control voltage is supplied to the PWM controller through an optocoupler (OP) for galvanic isolation from the high-voltage part of the PSU. Output voltages from the low-voltage windings of the transformer (LV) are fed to rectifiers and stabilizers. A voltage of 24-33V is required to bias the varicaps in the RF tuner module; 12V is needed to power the analog part of the circuit (video and sound); 5 and 3.3V - to power the digital part of the circuit. Troubleshooting begins with checking the diodes in the high voltage part of the circuit. Diodes in the low-voltage part of the circuit are also subject to failure. They also check resistors (for open circuit) and capacitors (break, swelling) in all parts of the circuit, low-voltage circuit stabilizers, Schottky diodes. It should not be forgotten that the diodes may seem to be serviceable, but have a leakage current. If this search does not lead to anything, and the troubleshooting of the transformer windings and chokes also does not bring results, then it can be said with confidence that the PWM itself and the elements must be replaced his bindings. It should be recalled that often a malfunction can be a non-solder at the points of attachment of the winding parts of the PSU - loosening of the contacts occurs due to the vibration of the elements at the operating frequency of the power supply. Finally, a little technical note. You should be very careful when choosing satellite equipment - the market is simply littered with fakes for well-known brands. You don't have to go far for an example - in the recent past, a device called Boston passed through my hands, which was an almost complete copy of the Korean Openbox brand receiver. After less than a month, the device failed. Conclusion - before buying, carefully study the device, check the manufacturer, do not be too lazy to look for information about the satellite receiver on the Internet (reviews, licenses). Speaking of licenses - equipment made in mainland China is quite reliable in operation, just don't run into a frank fake, made in no one knows where.
The equipment of European manufacturers in this respect is certainly beyond competition (compared to the Chinese one) - the simplest receiver shown in the picture (with the cover removed) from the German company Golden Interstar has been working in my country house for many years without repair. Consider all the above criteria for choosing equipment and you will not have to repair it!
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In this article, we will fix the most common breakdown in satellite receiver, namely, we will repair the power supply of this device. Why a power supply? Yes, because in 95% of cases of failure of the receiver, the culprit is the power supply. it may not turn on at all, it may turn on “halfway” (for example: the red indicator is on, and the green one, despite our efforts when a certain button is pressed, does not turn on and there are still a lot of signs), or some function may not work. And the cause of all these misunderstandings, in most cases, may be the power supply. We will repair the SVEC receiver, but functionally, on most of these devices, the power supplies differ only in the shape and location of the radio elements. The principle of repairing receivers is almost always the same.
Now let's visually inspect the unit and the board, for visible causes of failure (this can be a "bloating" of capacitors, burning out of the board or individual elements, etc.). If there are no visible reasons, then we look at the fuse. Even if it is not visually visible that the fuse has “burned out”, it is better, nevertheless, to check its integrity with the device. If the fuse is not working, do not rush to change it and try to turn on the receiver. Usually they don’t “burn out” just like that, on the contrary, for the most part, when there is an overvoltage in the network, they remain unharmed, and something else will definitely fail. This is how modern technology works. In general, we need to remove the power supply (in the figure it is marked with a blue arrow) from the receiver in order to check other elements.
After that, we proceed to check the main transistor, which is on the radiator. If we discard all professional terms, then we simply “call” it for a “short circuit”. These transistors constantly fail, are designated as follows: D13009K. The literal values can be different, but the numeric values must match. This transistor is in many receivers, but not all. Others have similar or may have microcircuits. This is not the point, it is important that in most cases it is power transistors or microcircuits that fail.
Next, solder the new transistor and diode into place. After that, you can check our power supply. We do it this way: we insert it into the receiver and connect only the power cord and the power button to it. We DO NOT connect the cable with wires that goes to the board with processors. We will check by output voltages, the value of which is indicated on the power supply, near the "socket" where the cable is inserted.
Moreover, I recommend buying an external tuner that does not require the inclusion of the computer's system unit itself (for example, Grand ua40ext.). such a TV tuner works autonomously and is a kind of signal switch - when it is inactive, then the image from the video card goes to the monitor, and when we turn on the tuner with the remote control, the signal from the computer is automatically turned off and a TV signal is sent to the monitor. Or you can listen to FM, or input a video signal from a miniature video eye on the front door, or place this video camera in the nursery, and monitor the situation in another room (kitchen).
But recently a problem arose: after turning on the TV tuner, it worked for a couple of minutes and turned itself off. Restarting led to the same result.
In general, we begin the autopsy. Naturally, the first and of course the right thought is nutritional problems. I will say without exaggeration that malfunctions with power supplies or supply voltage are the cause of breakdowns in radio equipment in half the cases.
The tuner is powered by a small pulse external adapter for 5 volts half an ampere. We measure the voltage at the input of the power plug - only 3.8V!
Of course, no digital TV processor chip will tolerate this. This is where the device turns off.
But what is interesting - at idle, the adapter shows the required 5 volts. We'll have to do an autopsy and the power supply.
The Chinese were too lazy to supply the PSU case with screws, so we will do it radically - we use a cutting tool.
Inside is a small scarf, in the style of a mobile charger. It is an electronic transformer with output voltage stabilization.
We're doing an inspection. The electrolyte at the power output looks very suspicious. It even seemed to be swollen and depressurized.
Having found a similar capacitor at 470 microfarads, we replace it. First you need to measure it with an ESR meter, but my device has not been completed yet, so I skip this item :)
The test showed that now the voltage of 5 volts does not drop even under load. We connect the PSU to the TV tuner and see that the output voltage is almost normal.
Now you can close the TV tuner case and connect it to the monitor. We check - everything works fine. Since then, two months have passed, no more such a defect has arisen.
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