You could do a force back light test .
Remove power cord, remove 1 side of the cable going between the main board and Power board. Plug in power cord and see if you get back light. The light should be on FULL since the main board is removed from the equation.
If backlight is fully bright then it could be the main board causing the problem. Any time you cant see main menu of the TV it also could be main board problem,
If you do force backlight test and the LED still do not look like htey are firing then it could be Power board or LEDs themselves.
Check voltage on CN802 and CNI801, proper low voltage should be listed there
Also CN201 pin 14 should be 1v-4v -> thats the diming signal
SOURCE: Samsung LN46C670 LCD TV not displaying picture
There is a good chance that the actual back lights are not working. This could be due to a number of things. The troubleshooting guide is here: http://www.toms-service-manuals.com/?do=search&mfg=Samsung&modelsrch=LN46C670&typekey=0&Search=Submit+Query
Hi Rick,
It appears to be a case of backlight failure. since you have replaced all the boards, inverter is ruled out. Some of the LEDs in the backlight array may have gone bad. Fault is repairable, but needs care and experience of opening and repairing the LED panel. Good luck.
Check and replace damaged component/s at its back-light inverter board, or replace this board as card basis. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts. It will be best to replace the inverter board as card basis. http://electronicshelponline.blogspot.com/ To some model sets; especially LED back-lighted types; the back-light inverter circuit will be part of the main power supply board [SMPS]. In such cases, the power supply board might need replacement. To some models sets, the back-light inverter and SMPS section circuit will be integrated at its main board itself. If so; the main board should be replaced. To some models of sets, all these section circuit will be integrated at its main board. If this is the case, you have to replace the main board.
I would count your losses and replace the TV.
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