I have an LG 32 inch LCD TV with a CCFL backlighting. It stopped working about 4 years ago with a Flashing "Red Power ON" indicator light and the LG service engineer replaced the power board.
Now it exhibits the same symptoms as before - Comes on for a couple of seconds, goes onto a Flashing Red Power ON indicator. This time, the service man says that the TV is obsolete and replacements are not available.
I decided to do some repair on my own, managed to get a schematic.
There are 2 H Invertors, each feeding 7 CCFL tubes in Parallel.
Each Invertor has 4 MosFets (5N52U). The observation is One particular Mosfet Q707 over heats. I let it run and it blew along with its lower partner Q710.
Since the original MosFets were not available, I replace all the 4 with 2SK1118, with exactly the same observation - ONLY Q707 overheats.
I believe that faulty CCFL will cause all the 4 transistors of the H bridge to overheat. I have confirmed that the 2 Resistors, The Diode and the Capacitor connected th that MoSFeT are in order.
I look forward to your comments and suggestions. Thanks
Now it exhibits the same symptoms as before - Comes on for a couple of seconds, goes onto a Flashing Red Power ON indicator. This time, the service man says that the TV is obsolete and replacements are not available.
I decided to do some repair on my own, managed to get a schematic.
There are 2 H Invertors, each feeding 7 CCFL tubes in Parallel.
Each Invertor has 4 MosFets (5N52U). The observation is One particular Mosfet Q707 over heats. I let it run and it blew along with its lower partner Q710.
Since the original MosFets were not available, I replace all the 4 with 2SK1118, with exactly the same observation - ONLY Q707 overheats.
I believe that faulty CCFL will cause all the 4 transistors of the H bridge to overheat. I have confirmed that the 2 Resistors, The Diode and the Capacitor connected th that MoSFeT are in order.
I look forward to your comments and suggestions. Thanks
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