LG 42LB5600 TV with faulty EAX65423701 PSU
Good day folks. Let's get straight to the point: I've got what I think is a pretty recent model of LG LED TV which has a power supply issue. The TV is a 42LB5600. I've searched around and I found posts about other models pretty similar to this, but not the exact problem (though I kinda know what to look for), so I'll leave my own thread here so that I can hopefully get some more tips from those more professional than I am (haven't quite worked with LGs that much).
The problem: the TV does not turn on and the power LED on the front is flickering (not flashing steadily as if TRYING to come on).
My thoughts based on what I read so far: bad PFC.
My observations so far (bare with me, as I haven't quite measured everything I should've, but I'll open the thread in advance anyway): the power supply is an EAX65423701. Plug the TV in and the power supply starts making a rapid ticking noise (4-5 clicks per second, in time with the LED flickering). The 3.5V stand-by is present at the connector for the main board. Applying 3 volts to the main board with a computer power supply keeps the LED lit steadily, so I highly doubt the main board is at fault. Disconnecting the main board from the power supply does NOT turn on the backlight - the ticking noise continues and no voltage comes out of the LED plug at the top ! The voltage at the main cap jumps between 317V and 322V in between each of those clicks, indicating that it tries to fie on but fails, as it should go up to around 380v and stay there, so I'm suspecting a PFC issue, though I haven't yet ruled out the possibility of something bad in the secondary causing the immediate shutdown. All the diodes that I checked are good. Fuses are good. Caps show no sign of wear (though I don't have an ESR meter on hand yet - will get one soon). Another thing I checked were those 4 SMD diodes on the back encircled in red in the third pic (7503 = 750 Kohms - can't see them too well due to the glare) and I find their values to be a bit low, only around 500 Kohms on all of them, which is strange, since resistors usually increase their resistance when they fail and not the other way around ! :|
What I haven't tried yet: reflowing connections to transistors/transformer etc, heating up the board while on, checking the power to those 2 ICs on the HOT side (which is going to be a pain, since they're covered in some sort of raisin and I can't even friggin' see what they are, let alone measure them !
).
That's about it for now...thanks in advance for all the help. Cheers.
The problem: the TV does not turn on and the power LED on the front is flickering (not flashing steadily as if TRYING to come on).
My thoughts based on what I read so far: bad PFC.
My observations so far (bare with me, as I haven't quite measured everything I should've, but I'll open the thread in advance anyway): the power supply is an EAX65423701. Plug the TV in and the power supply starts making a rapid ticking noise (4-5 clicks per second, in time with the LED flickering). The 3.5V stand-by is present at the connector for the main board. Applying 3 volts to the main board with a computer power supply keeps the LED lit steadily, so I highly doubt the main board is at fault. Disconnecting the main board from the power supply does NOT turn on the backlight - the ticking noise continues and no voltage comes out of the LED plug at the top ! The voltage at the main cap jumps between 317V and 322V in between each of those clicks, indicating that it tries to fie on but fails, as it should go up to around 380v and stay there, so I'm suspecting a PFC issue, though I haven't yet ruled out the possibility of something bad in the secondary causing the immediate shutdown. All the diodes that I checked are good. Fuses are good. Caps show no sign of wear (though I don't have an ESR meter on hand yet - will get one soon). Another thing I checked were those 4 SMD diodes on the back encircled in red in the third pic (7503 = 750 Kohms - can't see them too well due to the glare) and I find their values to be a bit low, only around 500 Kohms on all of them, which is strange, since resistors usually increase their resistance when they fail and not the other way around ! :|
What I haven't tried yet: reflowing connections to transistors/transformer etc, heating up the board while on, checking the power to those 2 ICs on the HOT side (which is going to be a pain, since they're covered in some sort of raisin and I can't even friggin' see what they are, let alone measure them !
).That's about it for now...thanks in advance for all the help. Cheers.
Attached Files
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...I should've seen it from a mile away and testing with a multimeter showed just that: a solid "beep" between pin 6 and GND...sorry, will measure again 
I attached a close-up of the MAP8800.
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