How to stop sansui sv2136 changing channels without a remote

Try here

http://elektrotanya.com/sansui_sv2118si_m28_chassis_also_lt1427_lt2127_sv1418_sv2136_sv2188.pdf/download.html

Circuit dagrams are in PDF, and cannot include by this window. If you wish to get some details, check the site linked here. Pull up older posts. Check the site in 'Mosaic' view. It will make search easy. http://electronicshelponline.blogspot.com/

tried to unplug and don't use for a while.

Have you tried taking the batteries out? Also, is there some sort of reset button on the remote?

To switch from cable to air or vice versa on most Sansui flat screen tv's including the SLED2280, go into the menu. Select "channel" on the screen. Press "enter" on the remote. Select "auto ch mem" on the screen. Press "enter" on remote. Select "signal type" on screen. Press right arrow button or right volume button on remote to change signal type (cable or air). To program channels into tv, select "automatic search" on screen then press "enter" on remote. Wait for search to finish.
I hope this helps you.
Bobya

If the light on the tv does not flash when you press and hold a button it is not getting a signal from the remote. Your remote is bad. Do you have a cable or satelite remote you can program to work your tv? If not I think you need to go buy a universal remote and set it up for your tv.

i have a 29'' sansui furrato sx , the picture tube is not swithcing on , but itz changing channels, and sound also is ok , can i do anything on my own

Sounds like AFT, AGC voltages are not proper. Contact any service technician. The main board of your TV has to be troubleshooted.
If the main system control memory IC is bad, this kind of fault can occur. This is a very small IC; have 8 solder terminals, and can be located very near to the main system control-chroma IC. Check and replace it. Be sure to replace it with the same number printed on it; in all respect. Otherwise, it won't go. http://electronicshelponline.blogspot.com/ Before replacing it, try a reset to this set, and then check.
There are two methods to reset TVs. The first is simple to do; a Hard Reset. The other is somewhat skilled; is a Factory Reset (System Reset). To make it a hard reset, just unplug the TV from AC mains wall socket, and re-plug it back after 15 minutes or so. If you do this by overnight is better. This procedure will make it a hard reset. If you want to make it a system reset [Factory Reset]; you have to enter its service mode option, and select the factory reset option. If you wish to get some details; check the site linked here.

found solution by holding down both volume buttons at same time which enables on-screen menu allowing to select channel auto program

You'll most likely need a Sansui remote made to work with your specific model TV. I have similar problems with my Toshiba TV. Check eBay.