Sanyo DP 50842 backlights not working flashlight shows that screen is working which board d I replace to fix inverter r led driver

Common issue, you have some shorted LED lamps in the panel and will need to be replaced, the LED driver section of the power supply is shutting down after a second or so because of over current, chances are its not a board issu

Sounds like a backlight problem to me. If you input a signal to the HDMI or Composite input and then it goes black have you tried taking a flashlight to the screen to see if the picture is still there but just dark? That would indicate a backlight issue. That model appears to be an LED edge lit backlight, so if the picture is still there after going black your going to have to trace out the backlight circuit and see whats going on. Usually with LED backlighting if it comes on at all then the LED's are good, its just the driver supply thats failing to keep them on. Some TV's have a small separate board that provides the backlight control, but i suspect with this model its on the power supply board and not the motherboard. Have you checked that board? It could be bad caps on the power supply board, check the voltages to the backlighting when it lights up and then when it goes dark. It could just be some failed capacitors on the power supply causing that voltage rail to drop off.

Back - light problem. 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.

U are on the right track - problem is caused by the board that drives the backlighting - the inverter board.

If you can get the number for the board it may be available on the cheap on ebay.

http://www.shopjimmy.com/toshiba-pk101v1780i-power-supply-unit.htm

invariably the LCD backlight inverter board or the LED driver board are the usual suspects. or the T.Con board

see the video below and follow the logic of elimination process
LCD LED TV Repair No Image Blank Black Screen Flashlight Test How to Fix...

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://electro-medical.blogspot.com/
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.

LED TV Repair Tutorial - Common Symptoms & Solutions ...

? 6:43
https://www.youtube.com/watch?v=8HG7efTMj78
Jan 3, 2014 - Uploaded by ShopJimmy.com
LED TV Repair Review & Overview-Common Problems - Symptoms, Solutions Click Here to BUY TV REPAIR PARTS: ...TVs inputs and outputs, this main board is connected to thebacklight inverter/LED driver via this ribbon cable. ... ofillumination for the screen and the board that drives thatillumination.

LCD TV Repair Tutorial - How to Replace the Backlight ...

? 2:30
https://www.youtube.com/watch?v=s3r1GZCA0K4
Dec 31, 2012 - Uploaded by ShopJimmy.com
Philips TV Repair Flickering Image On TV Screen Tutorial Guide How to ... Inverter on LCD TV Easy Fix Help Click Here to BUYTV REPAIR PARTS: h... ... How to Replace the Backlight Inverter Board in LG & Philips LCD TVs.Missing: restore ‎illumination

Sanyo 42 led lcd tv - Engine cork

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.

Sounds like backlight is dead. Shine flashlight on screen. Can you see video slightly. Replace inverter or some sets have inverter as part of power board. If led set replace led driver board. Also that may be part of power board.