Friends,
I wish to Share with you my repair experience on an LG-LED LCD TV, model: 47LW5700-TA.
Problem with this TV was: when I was watching a program, it got turned itself off. When I press power ON again, TV has no display & no sound. Although the TV has its power supplies turned ON (I determined this from the operation of Power ON LED, It cycles from dark to Red, in slow motion every 2 seconds or so, meaning the Mother Board has DC voltages and it is waiting for some feedback signals before turning ON Back lights, T-CON etc).
I am sure, no one designs their TV circuits to fail exactly after the product warranty period is over! But alas, there is somewhat unreliable partner, which is the manufacturing process, to put together electronic devices on a PCB. (be it BGA, SMD, Soldering and other manual assembly processes involved with that Board). Quality of the board depends on these processes + ageing / environmental effects such as heat, moisture etc.
With this in mind, I tried various ways to solve this issue. And to cut my story short, the real reason for the fault is due to some of the digital circuits, not making communications within the Mother board. Therefore, we are seeing the power LED cycles from dark to red in slow motion, an indication that some link is missing.
Solution: I Used a hot air blower on digital ICs, which I suspected may have poor solder / joint connections (smd/bga chips with tiny pins bound to have this problems from time to time)! I set the temperature to around 320 degrees and slowly applied HOT AIR onto RAMs, processors, EEPROMs, NVRAMs, QIPs etc (one needs to ensure these chips don't get burnt...of course) so as to improve their "leads connections" onto the PCB tracks. Then, I let the chips cool down (5 to 10 mins). After that, turn ON the tv... Bingo... the TV works for me...
Simplified power ON operation of the TV:
when you hit the power ON switch, mother board should send the PS_ON signal to the POWER Supply Board, to turn on the PFC Voltage booster and the 12V/24V SMPS section. after slight delay, MOBO should send the BL_ON and diming control signals that are routed through the power supply to the inverter board to turn on the back light LEDs, and at the same time the processor on the main board will send the T-CON ON command, to turn on the MOSFET, to supply the 12V to the T-CON board and then the other processes will take place. This a general POWER ON cycle operation of a TV.
Hope this information will help someone in their understanding of a fault better and repairing it further.
I wish to Share with you my repair experience on an LG-LED LCD TV, model: 47LW5700-TA.
Problem with this TV was: when I was watching a program, it got turned itself off. When I press power ON again, TV has no display & no sound. Although the TV has its power supplies turned ON (I determined this from the operation of Power ON LED, It cycles from dark to Red, in slow motion every 2 seconds or so, meaning the Mother Board has DC voltages and it is waiting for some feedback signals before turning ON Back lights, T-CON etc).
I am sure, no one designs their TV circuits to fail exactly after the product warranty period is over! But alas, there is somewhat unreliable partner, which is the manufacturing process, to put together electronic devices on a PCB. (be it BGA, SMD, Soldering and other manual assembly processes involved with that Board). Quality of the board depends on these processes + ageing / environmental effects such as heat, moisture etc.
With this in mind, I tried various ways to solve this issue. And to cut my story short, the real reason for the fault is due to some of the digital circuits, not making communications within the Mother board. Therefore, we are seeing the power LED cycles from dark to red in slow motion, an indication that some link is missing.
Solution: I Used a hot air blower on digital ICs, which I suspected may have poor solder / joint connections (smd/bga chips with tiny pins bound to have this problems from time to time)! I set the temperature to around 320 degrees and slowly applied HOT AIR onto RAMs, processors, EEPROMs, NVRAMs, QIPs etc (one needs to ensure these chips don't get burnt...of course) so as to improve their "leads connections" onto the PCB tracks. Then, I let the chips cool down (5 to 10 mins). After that, turn ON the tv... Bingo... the TV works for me...
Simplified power ON operation of the TV:
when you hit the power ON switch, mother board should send the PS_ON signal to the POWER Supply Board, to turn on the PFC Voltage booster and the 12V/24V SMPS section. after slight delay, MOBO should send the BL_ON and diming control signals that are routed through the power supply to the inverter board to turn on the back light LEDs, and at the same time the processor on the main board will send the T-CON ON command, to turn on the MOSFET, to supply the 12V to the T-CON board and then the other processes will take place. This a general POWER ON cycle operation of a TV.
Hope this information will help someone in their understanding of a fault better and repairing it further.