Hitachi 50SBX78B 50" Rear Projection TV

Samsung TVs have three boards, ie, video card (center), input (control) where a single button control/inferead and HDMI s are connected and a power board where 120 volt is plugged in. A chip checks all the circuits before powering up the TV. Usually, fail in the high voltage circuit will cause many issues.Check the high voltage for at least 390 volts at the capacitor after the tiny high voltage transformer, as the power board supply all the other circuits, ie the backlights.

Do a hard reset to the unit, unplug the unit for at least 2 hrs and then turn it back on it should work fine.

Fault with the main power supply regulator board. Check and replace damaged component/s at its main power regulator [SMPS] section circuit. Contact any service technician. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts.
http://electronicshelponline.blogspot.com/
It will be best to replace the power supply regulator board as card basis rather than making "Surgery" to it; which usually will make loss for both money and time. Even though you can make it right, it will cost around an amount equal to the cost of a new board; including the cost of (spare parts + service charge) More to say, most of the spare parts to it will be difficult to get from open electronic spare part market. This is true to most of the flat panel TV power supply boards; irrespective of its brand and screen size.
After replacement of the power board, Va&VS voltages are to be set according to the silk screen; can be located at the display panel, and it is a must for plasma displays.

first place to begin is if able test voltages in and out of the power board inside the set---if not able to do that consider having a shop look at it.

If you get it open:

if no any power light indicator at the front of your tv that was mean the unit is dead set or no voltage that is circulating in the main board and other boards.if you can remove the rear cover of your tv, the first place to check will be the power supply board if the primary fuse was blown. if the fuse is blown with darkened color that was mean has shorted component either in the main board or in the power supply unit. if the fuse blown with clear color just replace with the same rating.

Have no picture can be caused by bad T-CON board, bad main board, bad 24vdc power supply for the backlight inverter board, bad backlight inverter board. You need to get some basic understanding how LCD flat panel works so it will guide you how to go about troubleshooting it because I am not going to tell you to throw in the boards until the problem is solved, it can get real expensive.

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.

1 swollen Capacitors / Replace
2 blown Diodes on inverter board / on some # 508 or 908
3 bad transistors in inverter bad will appear overheated powdery coat
4 replace inverter if you cannot locate problem on it
there is a safety built into the high power back light supply and that is if too much current is drawn or light is shorted it will not burn up
or hazard high volt shock to user.
capacitors and diodes driven with power transistors
look for darkened spots on the board to identify hot transistors
puffy tops and leaky bottoms of capacitors

when you turn it on does the bottom or top of the screen show image a Milli second before the other it should be evenly the lag
is the one requiring more amperage

It can be that the 24vdc power supply section has gone out or short circuits in the backlight inverter circuits, those are the two areas you need to check out, another posibility is the dead T-CON board. Please read my guide to get some understanding how the LCD flat panel TV works.

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 are some troubleshoot 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

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

What is the make and model number of the set your trying to repair? Post that information and I will be able to possibly help you out.

Probably has some bad solder connections in the deflection/ power supply area, if you dont know about electronics, might call a repairman and put a few hundred $ into it or junk it, also it is not HD, just FYI