SAMSUNG LA26R71 LCD COLOUR TELEVISION: TROUBLESHOOTING AND REPAIR

LCD TVs are today’s’ most trend and they are slowly replacing picture tube based televisions, all over the world. Comparing to picture tube based televisions, these LCD or Plasma TVs are more venerable to faults, and are not long lasting.  More over, with LCD TVs, with lower frame rates are very troublesome to see the fast moving objects.  In most LCD TVs, this is a main drawback comparing to picture tube based TVs.  Fast moving objects will appear as jerking across the screen. With increased frame rate, this drawback can be rectified, but the cost of the TV will go high.

The repair work to LCD and Plasma TVs are very easy, comparing to picture tube based TVs, as only few replicable components are there on its boards. In most repair cases, board replacement should be done, as, there will be no replicable components, by normal disordering and soldering methods.  Mainly an LCD TV will have a main board, called “Logic Board”, which have most of the main functional, lie video processor, DDR RAM, main microcomputer, audio processor, audio output, sub microcomputer, tuner and memory sections.  Next to it, a video card, contains low voltage differential signal processor, multiple output regulator, dynamic random access memory, and two or more operational amplifiers and an EEPROM [Electrically Erasable Programmable Read Only Memory].

The third one to say is its backlight inverter card.  It will have a DC to AC converter, two comparators, four or more MOSFET [Metal Oxide Semiconductor Field Effect Transistor], used as outputs. This board in turn controls the backlight of the LCD TV.  According to the screen size, the number of backlight CCFL [Cold Cathode Fluorescent Lamp] lamps will increase, and the number of MOSFET outputs and CCFL drive transformers will be.  For a 26” LCD television, there will be at least 12 CCFL lamps.  This lamp driver board otherwise called as lamp inverter board is venerable to defect in most LCD TVs, irrespective of brand and model.  We can come to details later; now get a general idea about what are boards in an LCD TV, and their functions.

The fourth one is the main power board, which supplies all the power to other boards to work. The power board of different LCD brands has different circuits, but the output voltages comes from it will be almost the same.  Here I refer the circuit of SAMSUNG LA26R71.  A 26” LCD TV.

As stated earlier, there are mainly these four boards will be there for any standard LCD TV.  Some advanced models will have two more boards, which are used for surround sound output.

Let’s have a look at the power supply inverter board [SMPS] of the above said model.  I’m here to report some main faults I’ve got serviced.  So many other faults may occur, as a TV is composed of thousands of small components soldered together, each and every component in it has its own function when TV is switched ON.

To be continued: on Part-2