I am working on a 40'' lcd flat screen tv model tcl l40fhdm11, the top half of the screen is normal but the bottom half is yellow greenish,how can i fix

sounds like a board or cable connected to the board

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.

power board defect

0174,0179,0173,1070. Try these codes. If you wish to get more, try the following links. Both the sites linked have set-up code list & set-up procedure to many popular brand remote controls.
http://electrohelponline.blogspot.com/
http://electro-medical.blogspot.com/

If it is an LED LCD TV, the backlight inverter board should be troubleshooted. Contact any service technician.

Depending on the brand, it's likely that the color guns are out of alignment, or some of them are faulty. If bumping the TV has any affect on the picture, this is your problem. If the TV is a newer TV, this should be covered under warranty. If it is past warranty, the parts are available from the manufacturer. It's not "easy" to replace these parts, but it is doable. Good luck to you!

tcl tv

the red shadow is a power shortage

update your tv softwhere

Most RCA Codes Will Work Depending On Your Remote.