This LG 26LD350-ZA TV suffered from premature oxidation due to proximity to an air conditioner indoor unit output. It tries to start, red LED blinking, then solid blue and after a few seconds it goes back to red.
Visual inspecton: greenish oxidation in PSU axial components. Ceramic caps C502 and C504 legs are close to break. Same for all 3 LiteON LTV-817-BN photocouplers, with very rusty top legs. Solder side with some oxidation in large tracks, but nothing cut or severely affected.
I brush off most evident oxidation from circuit and components and replace mentioned ceramic caps and photocouplers. No changes. Then I read voltages: they're all present, but "24V" are 28V and "12V" are 14V. Inverter ERROR line is at 3.3V (=error). Panel specs (AUO T260XW04 V.3) show that above 26V is an abnormal condition. Inverter fuse is OK.
I disconnect Inverter from PSU and short ERROR line with GND. TV turns on and sound can be heard. There's something wrong with 24V and 12V, and both are driven from IC100 (ST half-bridge switcher L6599D) and both have common feedback/regulation.
Check secondary side feedback circuit and discover that R255 (10kΩ 1%) is open! It's directly connecting 24V to a photocoupler (I can check schematic from very similar PSU LGP32-09P, schematic posted somewhere in this forum). Replace it and it's working, with normal values at 24V and 12V lines.
Visual inspecton: greenish oxidation in PSU axial components. Ceramic caps C502 and C504 legs are close to break. Same for all 3 LiteON LTV-817-BN photocouplers, with very rusty top legs. Solder side with some oxidation in large tracks, but nothing cut or severely affected.
I brush off most evident oxidation from circuit and components and replace mentioned ceramic caps and photocouplers. No changes. Then I read voltages: they're all present, but "24V" are 28V and "12V" are 14V. Inverter ERROR line is at 3.3V (=error). Panel specs (AUO T260XW04 V.3) show that above 26V is an abnormal condition. Inverter fuse is OK.
I disconnect Inverter from PSU and short ERROR line with GND. TV turns on and sound can be heard. There's something wrong with 24V and 12V, and both are driven from IC100 (ST half-bridge switcher L6599D) and both have common feedback/regulation.
Check secondary side feedback circuit and discover that R255 (10kΩ 1%) is open! It's directly connecting 24V to a photocoupler (I can check schematic from very similar PSU LGP32-09P, schematic posted somewhere in this forum). Replace it and it's working, with normal values at 24V and 12V lines.
