Chosen Solution
To those awesome enough to give my “heavily budgeted” self an honest opinion and/or educated guess. Picked up this LG TV for $20 on local buy/sell/trade. Guy was nice enough and honest about the condition. It worked great for years, then about a week before I bought it, it doesn’t turn on — pressing the power button starts the status LED to fade dim to bright forever. A preface to the following: I worked managing an SMT production line for small r/c and robotics for nearly a decade. I can get by if it has a circuit board, but this also means I might be making incorrect assumptions. I did a thorough inspection of the power supply, checking electrolytics for the obvious signs of poopiness. Nothing apparent. The voltages on the PSU terminal to the mainboard appear to be normal when off, 3.5V (3.481V) on the 4 conductors from PSU to MB, all else seem to float low. Upon hitting the power button, all 12V are 12V and all 20V are ~22V (model dependant I’ve read). The power on pin, blue wire/pin 1, is the same 2.481V in this state. A-dim reads 2.967V and P-dim reads 85mV. Error reads 92.2mV. Poking around the PSU with my trusty Klein meter, I am seeing a lot of 385V and some intermediary values like 80V and thereabout. What i don’t see is what I believe to be the backlight stage outputting any voltage at all. There are two vertical voltage regulators screed to an aluminum ground/heatsink that start at 5.4V or so and wind down to ~4.5V then jump up again over about 10 seconds. There is another next to that at double that voltage. It appears the voltage is being transformed up properly, but not able to be piped to the backlight. Maybe… Whatever the case, I have a choice to make. If it’s the mainboard, this is going to the recycler. If it’s the power supply, it’s worth throwing $40-$45 at for a 120hz panel, but not $140 for the mainboard. What do you guys think?
@thenrz it’s a bit of a beast to really give you a definite answer. There are more issues with the main board on this model than the power board and going by your voltages it sounds like your power board is supplying what you TV needs to function. That would leave the main board as the culprit. You could try to check some other things like applying a jumper from the 3.3V to the pwr pin to check and see if you get 12V on the other pins. Also check your backlight by applying a jumper to backlight signal on (BL ON), just make sure that you disconnect the main board when you do that. For further testing you can always use the power block diagram 47LD450-UA_COVER
