To open a Sony rm D.C. 400 remote

SOURCE: Opening the case of a JVC Remote Control

Not having seen that particular one, remote cases usually have a couple screws under the battery to lock the case together and then a number of plastic tabs around the perimiter that hold the joint closed. find the screws (sometimes they hide them under labels) - I don't know what it is about screws that manufacturers don't like to show. Either think they are not cosmetic or don't want us take-it-apart maniacs to get in. Anyway, get the screws loose then (this is the hard part) carefully pry open the case joint, feeling where and how the tabs snap out and then be careful not to have everything inside go flying when the last one lets loose. Almost impossible to not leave little gouge marks in the joint.
Hope Ya Fis It!

SOURCE: Insignia TV code for Sony remote RM-V302

press tv, hold setup til tv blnks twice and release setup, type 10463 then power. 5 digit code not 4 like most.

SOURCE: Code for Sony RM-V310A remote.

How do I program sony universal remote RM-V310A for a polaroid flat screen TV

SOURCE: Sony remote RM-DX500 not working with Disc

There are 2 set's of command switch's for the dvd player, a 3 position command switch on the back side of the dvd player and another 3 position command switch on the inside of the remote right next to the batteries, easiest option is to remove batteries from remote and test each one of the 3 position switch's labeled 1,2 & 3 and test remote control.

SOURCE: how can i open my sony rm-ed009 remote control

insert wide flat blade (such as a wide flat bladed screw driver) into seam along one side. Twist carefully until seam starts to prise apart - carry on until you hear the "crack" of the press-tabs coming apart and repeat along the the length of the seam until you can carefully pull it apart.