I have exhausted the resources here and elsewhere to the best of my ability.
Observations, then what I've tried:
Observations:
1) There are 4 CCFL's attached via two connectors: CN301 & CN304. It doesn't matter which CCFL cable is plugged into CN304: That cable's lamps illuminate and stay lit indefinitely just fine, provided there's no video input. It doesn't matter which CCFL cable is plugged into CN301: That cable's lamps never illuminate, with or without video input.
2) Without video input, the lamps on whichever CCFL connector is attached to CN304 are lit fine, and the "No Video Signal" graphic floats around the LCD. Upon applying video signal input, all lamps go dark in 2 seconds.
3) Without video input, there's 15VDC relative to chassis ground on both leads of F301 (power input to the inverter). Two seconds after video signal is applied, this increases to 21VDC.
4) Inverter transformer T301 has 8 pins with in-circuit resistance readings as follows: (I have pin #'s in red on the foil side photo)
Pin 1 to 2: 0 ohms
Pin 2 to 3: about 0.2 ohms, both meter lead polarities
Pin 3 to 4: 500 ohms in one direction; about 6K-ohms with cap charging behavior in the other meter lead polarity.
Pin 5 to 6: 1050 ohms (this goes to CN304)
Pin 7 to 8: 980 ohms (this goes to CN301, the CCFL port that's always dead)
5) This board doesn't appear to have any V sense capacitors. There's no evidence anything was ever soldered into C303 or C304. An identical board #LS24CMKKFVC listed on eBay also doesn't have these cap's.
6) This board appears to only have load capacitors at CN301 (C301 & C302).
7) There is very mild darkening of the board next to T301, so I guess the transformer runs warm, but I see this a lot even in working units.
8) There is no sign elsewhere of any thermal issue or suspect solder connections.
What I've done:
I've replaced every electrolytic capacitor on the board except for the tiny C111 which appears to be associated with the user control button input connector. I used all new Nichicon 105°C capacitors from DigiKey of the exact capacitance & voltage rating as the originals, some of which were "Sam Young" brand, but none of these showed any signs of bulging or leakage. Absolutely zero change in the above symptoms, observations and readings after doing this.
Ideas?
Observations, then what I've tried:
Observations:
1) There are 4 CCFL's attached via two connectors: CN301 & CN304. It doesn't matter which CCFL cable is plugged into CN304: That cable's lamps illuminate and stay lit indefinitely just fine, provided there's no video input. It doesn't matter which CCFL cable is plugged into CN301: That cable's lamps never illuminate, with or without video input.
2) Without video input, the lamps on whichever CCFL connector is attached to CN304 are lit fine, and the "No Video Signal" graphic floats around the LCD. Upon applying video signal input, all lamps go dark in 2 seconds.
3) Without video input, there's 15VDC relative to chassis ground on both leads of F301 (power input to the inverter). Two seconds after video signal is applied, this increases to 21VDC.
4) Inverter transformer T301 has 8 pins with in-circuit resistance readings as follows: (I have pin #'s in red on the foil side photo)
Pin 1 to 2: 0 ohms
Pin 2 to 3: about 0.2 ohms, both meter lead polarities
Pin 3 to 4: 500 ohms in one direction; about 6K-ohms with cap charging behavior in the other meter lead polarity.
Pin 5 to 6: 1050 ohms (this goes to CN304)
Pin 7 to 8: 980 ohms (this goes to CN301, the CCFL port that's always dead)
5) This board doesn't appear to have any V sense capacitors. There's no evidence anything was ever soldered into C303 or C304. An identical board #LS24CMKKFVC listed on eBay also doesn't have these cap's.
6) This board appears to only have load capacitors at CN301 (C301 & C302).
7) There is very mild darkening of the board next to T301, so I guess the transformer runs warm, but I see this a lot even in working units.
8) There is no sign elsewhere of any thermal issue or suspect solder connections.
What I've done:
I've replaced every electrolytic capacitor on the board except for the tiny C111 which appears to be associated with the user control button input connector. I used all new Nichicon 105°C capacitors from DigiKey of the exact capacitance & voltage rating as the originals, some of which were "Sam Young" brand, but none of these showed any signs of bulging or leakage. Absolutely zero change in the above symptoms, observations and readings after doing this.
Ideas?
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