I need a manual for a Sharp 19NV88BK television. The volume is stuck in the stereo mode, cannot lower it manually or with the remote. TV responds to remote except the volume.

Fault at its main digital board. Short circuited component/s at it. Contact any service technician; or the authorized service center. If you wish to get some details; check the site linked here. Pull up older posts. http://electronicshelponline.blogspot.com/ In most cases, the main board might have to be replaced. If so, a software [firmware] update too might be necessary.
Before going further; try a hard reset first. If it does not help you, replace the main digital board. 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; visit the site linked here. ....

Fault at its main digital board. Short circuited component/s at it. Contact any service technician; or the authorized service center. 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/
In most cases, the main board might have to be replaced. If so, a software [firmware] update too might be necessary.

U already change the remote control for brand new batteries wright?Yes.Remote controls devices are heavily depend on it CPU chip for all of it functions.Test the tv manual buttons like Power,Menu,Volume - + and Channel + - all work?Yes.The tv remote control CPU is dead that why doesn't read the tv infered laser signal at all.Try website like Remotes.com to buy an original remote for the replacement.

turn off manually and turn on it should work better than before

Code for? childlock? remote?

The link above does not work.

unplug the unit and plug it back in see if it resets

unplug and plug back in.