Chosen Solution
Own a UN55H6350AFXZA and have the same exact issue with it - no backlight, no picture. When I power on , STBY led light blinks 6 times and then stops. When i disconnect the cable between the main and power board, back light comes up fine. T-CON is good . Checked voltages on the power board on two connectors - CNM803 (with power on i see 12.8v, with power off i see 10.54v), CNL802 (0,0,334v,0,223v,0,223v,0). Replaced the power board (sj) and the main board (ebay, out of stock @ sj), no change. Replace t-con (shop jimmy)and same problem. Replaced the cables and ribbon - no change. Checked the voltages on Main board as per service manual and found lot of discrepancies. The surprising this was that i found the same discrepancies with both the boards (ebay & original) - then started to wonder what are the chances . So, at this point, I have a strong suspicion that the issue is with Main board , but trying to process the voltage test results on both the main boards.
rturlapati your power supply has the right voltages for your backlight and obviously the backlight works since it comes on when you disconnect the main board from the PSU. This would leave the main board as the culprit since it provides the signal for the backlight enable. Check for 5V on connector CN201 pin 4 let us know what you get If you do not have that voltage it is a PSU issue). After that check pin 11,12,13 on CN201 for 13V and let us know what you get on that (If you do not have that voltage it’s a main board issue).
