How to test tuner on 40lc45s

Have you tried,
1 Changing the source.
2 Changing the batteries in the remote
3Getting a replacement remote or pushing the buttons on the tv itself
4 Asking a pro

This could be the tuner overheating and sending a signal from the tuner board CPU to the power board to instruct the tuner to turn off. Check that there is adequate ventilation in the TV. Try testing with a fan to see if that changes the behaviour of the loop that you get.

the chroma ic could be shorting

This TV has a well known problem with the back light inverter board.

See
https://www.youtube.com/watch?v=cDAwGTP3RLY

Hope this helps!

check bad component parts at the power supply board as will as burnt parts.

Try changing the input device to something you are sure, works such as a DVD player. Switch off TV manually, switch off power, remove plug and retry after 48 hours. If problem persists, please refer it to a qualified service technician.

1) test the button from channel for dirty , open or defective.
2) test the TUNER, lubricate tuner contacts.
3) see tuner, i-f, video detector, AGC , rfamp/converter ,amps, circuit see the block diagram
God bless you

The tv problems u are decribing are 50/50 it could be the main board tv Tuner signal board is dying and shorting out or the tv LCD screen panel itself are leaking radiation and slowly shorting out.Tries websites like Shopjimmy.com,Ebay.com to buy a refurbish main board tv Tuner signal board for the replacement.50/50 could get this tv fixed by replacing this main board tv Tuner signal board.If after u replaced the board and still have the same problems,than u know for sure it is the tv LCD screen is dying and leaking radiation and slowly shorting out.Than u know for sure this tv is not worth as a whole tv anymore,now only as salvages tv for it PCB circuits boards only.U can return the main board tv Tuner signal board to the dealers.Get some money back,but must lose some money,like subtraction like from the shipping and handleling cost and the useually the 10% restocking fee.

Go here:
http://www.oncorpus.com/down/2009/40LC45S-UM-Eng.pdf

http://www.oncorpus.com/Product/LCDTV/19LB30QD.htm