Repair of DVB-T2 tuner Globo GL50. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Television, video equipment

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In the article, the author shares his experience of repairing a tuner for receiving terrestrial digital television programs. The troubleshooting technique he described is also applicable to other electronic products where one or more functional units are powered by a voltage stabilizer with unknown output parameters.

Tuner "Globo GL50" is designed to receive DVB-T/T2 terrestrial digital television programs, as well as to play multimedia files from external media connected to the USB port of this set-top box. After working for about a year, this tuner broke down. The failure looked like a complete inoperability of the device, while the LED on the front panel glowed yellow. Repair of such devices is usually impractical, but since there are few interesting parts in modern digital devices for further use, it was decided not to disassemble the receiver into parts, but to try to repair it.

The troubleshooting was started by checking the operability 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. Further, on the block board (its marking is M3103-0C), integrated voltage stabilizers were checked. At the output of one of them (KV3VC - according to the scheme of the U4 microcircuit) there was a voltage of 0,537 V, while the microcircuit case was heated to a temperature above 100 ^оWith five minutes. This stabilizer directly feeds the tuner's CPU, which remains cool. The initial version that one of the ceramic blocking capacitors C23, C24, C35 was broken was not confirmed.

Turning off the load of the stabilizer did not change the situation: the microcircuit case also got very hot. Since no useful information could be found either about the failed microcircuit or about the board itself, it was necessary to find out what voltage was required for the operation of the central processor experimentally. To do this, the U4 chip was soldered from the board, and the output of a powerful laboratory regulated power supply was connected to the printed conductor intended for soldering its output pin (the closest contact next to the inscription "U4"). At a voltage of 1,1 V or less, the tuner processor worked with errors or hung. At a voltage of 1,2 V, the processor worked without errors in all modes of operation of the set-top box, consuming a current of about 0,6 A.

Since even if it were possible to find and purchase the same microcircuit to replace the failed one, its installation, according to the author, is devoid of practical meaning (what burned down once will burn out the second and third time); It is not enough just to fix the problem, you need to eliminate the causes of its occurrence. It is likely that the KV3VC integral stabilizer burned out from overheating - a typical malfunction of modern digital devices, ranks first in the number of failures of household and industrial devices (printed wiring is in second place, and together they "take" more than 90% of all malfunctions that arose not due to improper operation).

It was decided to replace the faulty switching stabilizer microcircuit with a linear stabilizer with an output voltage of 1,3 V on the KR142EN12A microcircuit, 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 unchanged), the lower the output voltage. Capacitors 1C1, 1C2 - blocking. Diodes 1VD1 - 1VD3 protect the load from damage in case of 1DA1 malfunctions. Taking into account the voltage drop on the connecting wire, the output voltage of the stabilizer turned out to be approximately 1,28 V.

Rice. 1. Stabilizer circuit

The details of the new voltage regulator are placed on a 22x22mm circuit board. The KR142EN12A chip is installed on a ribbed duralumin heat sink, which is tightly pressed against the bottom and side walls of the metal case of the attachment. 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 getinax washer are put on the fixing 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 package (for example, LM317, KA317). The purpose of the conclusions 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 attachment

The input of the stabilizer is connected to the fusible insert F1 (Fig. 3, red wire), the output is connected to the inductor L4 (Fig. 4, green wire), and the common wire is connected to the negative plate of the capacitor C35 (Fig. 4). Instead of diodes 1N4001, you can use any of KD208, KD243, KD247, 1 N4002-1 N4007.

Rice. 3. Circuit board

Rice. 4. Circuit board

M3103-0C circuit board can be used in other DVB-T2 receiver models. Since the author has never come across "cold" DVB-T2 set-top boxes (all of them get very hot during operation), after the end of the warranty period it is advisable to measure and record the input and output voltage values ​​​​of the stabilizers installed on the board, and also 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 simultaneously formed at the output of a pulsed integral stabilizer. To improve cooling inside the console, you can install a small "laptop" fan.

After the repair, the current consumed by the tuner from the power source was about 0,75 A, which means that the external bundled switching power supply with the output parameters indicated 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 2,5-inch hard drive connected to it. If the set-top box is equipped with a power supply built into its case, in order to reduce the load on it and, accordingly, to reduce the temperature inside the case, it is advisable to power 2,5 '' hard drives from an external unit.

Author: A. Butov

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