Repair the TV power supply TV BBK LD1912KToday, a TV with a built-in DVD player BBK LD1912K is being repaired. The TV did not react to the POWER in any way, which naturally meant that in 90% the malfunction was in the power supply.
When disassembling such TVs, you must be extremely careful, since the power supply board and main are attached to the back cover, and all connections are made using loops that must be disconnected beforehand.
Disconnecting the matrix cable during disassembly
In this TV, the power supply is made by a separate board, which is located at the bottom of the TV, and produces 12 volts.
First of all, I checked the presence of 12 volts at the output of the power supply. The measurement results showed a complete absence of output voltage.
Measurement of 12 V at the output of the power supply
220 volts at the input of the power supply turned out to be available, which fully confirmed the failure of the power supply.
Measurement of 220 volts at the entrance to B.P.
I immediately decided to measure the voltage on the mains electrolyte. The measurement result showed that there was only 195v, instead of 280v, which indicated that it was malfunctioning.
Measurement of voltage on the mains electrolyte
This TV uses the power supply model HGP-KS03 / REV5-2. As a controller PWM, the LD7575PS chip is used. Burned resistors on the negative bus immediately rushed into the eyes, the value of which could no longer be determined, since they were very burnt. The burned resistance from the gate of the field-effect transistor to the housing is also visually visible.
Burnt Parts of HGP-KS03 / REV5-2 Power Supply
Having removed all the defective elements, I replaced the 100μF capacitor with 400 volts, the voltage at which I measured earlier. After the replacement, the voltage rose to 284 volts, which was already in line with the norm.
Mains capacitor voltage after replacementNext, a field effect transistor was checked, which turned out to be open. It is very interesting that there were no signs on the transistor. I decided to put a transistor brand P6NK60ZF, which I often use as a universal replacement in power supplies.
After installing the field operator, he began to test the LD7575PS. Having downloaded the datasheet on it, I saw that food should come to her on the 6th leg. In order to eliminate the short circuit of this PWM, it rang 6 legs (VCC) and 4 (body). As a result, it turned out that the microcircuit is broken, and it must be replaced.
Breakdown LD7575PS between 4 and 6 legsHaving installed the new LD7575PS, I checked all the other elements, but did not find anything suspicious.
It remained to find the values of the burnt resistors, and install them on the board. At this point, I had the greatest delay. In the datasheet on the LD7575PS, a connection diagram is shown, without specifying the element ratings. In the search, I began to look for block schemes assembled on the LD7575PS, but many schemes were built on a slightly different principle, and the ratings were very different. As a result, I found a more or less similar circuit, where instead of assembling 4 resistors, 1 resistor of 0.56 Ohms was used, and the resistor from the gate to the case corresponded to 10 kOhm.
I did not find a resistor in the smd case; I installed the usual 0.36 Ohm mounted mounting. It turned out not very beautiful, but the main thing is reliable.
The final version of the power supplyTurning on the power supply, the output appeared 12v.
The power supply after repairHaving collected the TV, it started.
TV at workWho cares, the picture shows all the flown out elements of the HGP-KS03 / REV5-2 power supply.
Replaced parts on the HGP-KS03 / REV5-2 power supplyDownload the datasheet on the LD7575PS chip by the link below:
LD7575.rar
TV BBK LD1912K