While you have the back cover off, test the panel and power supply board by disconnecting the cable from main board. If unit's backlight comes on the main board needs replacing. If the backlight does not, the power board needs replacing.
SOURCE: no picture
The way to isolate the failure to the power supply would be to measure the voltages going to the backlight inverter board. If all the voltages are normal then is more likely a defective backlight inverter board or LCD controller board.
SOURCE: Samsung LNR408DX/XAA Powers on with sound but no picture
I think you need to exchange the Main Board.
SOURCE: tv will not start after power surge
Voltage checking and caps inspection will be the first thing to do.
If you can post the pictures, that will help a lot. Look at the inverter board to see if you are getting 12~18vdc feeding it, also look for caps with leaking/bulging top.
See some pictures here:
http://s807.photobucket.com/home/budm/allalbums
http://en.wikipedia.org/wiki/Capacitor_plague
Testimonial: "Example pictures quite helpful. I do some more visual checks and then post pictures of my power supply and ask for test locations. Thanks"
SOURCE: I have an insignia NS-LCD37HD that has backlight
Chec to see if you are getting 12vdc at the T-CON board power input pin first.
First, look at the screen in darkened room to see if you can see any slight glow from the screen, if it does, then the problem can be the T-CON (not getting the 12vdc) or the main logic board not feeding the signals to the T-CON board.
if not, next place to check will be the power supply module, make sure it has 24vdc which is required by the backlight inverter to work, the reason for not having 24vdc can be from bad DC filter caps (leaking/bulging top, high ESR) or short circuits in the inverter board which will cause the 24vdc supply to go into shutdown mode, so you may have to disconnect the power cable that feed the inverter board to see if the 24vdc will work without the inverter board hookup, you will need to apply about 3~4 amp of load to the 24vdc to make sure it can handle that. There are fuses on the backlight inverter boards also. So there is some troubleshooting you will have to do to find out the causes of the problem you are having.
If you are going to DIY and have proper tools, electronics knowledge, and know safety precaution then please read on:
Please see my basic troubleshooting guide here:
http://www.fixya.com/support/r5093881-lcd_flat_panel_tv_troubleshooting_guide
Failed TV and Monitors: http://s807.photobucket.com/home/budm/allalbums
http://en.wikipedia.org/wiki/Capacitor_plague
Parts: www.shopjimmy.com
Capacitors kit: http://lcdalternatives.auctivacommerce.com/Default.aspx he can make you a set of caps.
Testimonial: "So far so good! Almost got it figured out. Thanks!"
SOURCE: I have Samsung UN46B8000XFXZA LED TV. After power
Yes based on your testing it appears that the power supply is at fault solely and you can opt to attempt a repair or replace it altogether. Unfortunately you will not be certain that the main board does not also need to be replaced until you have repaired the power supply.
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