If you buy a DVD from another country and try to play it in your Sony DVD player, you may find that the player won't recognise the disc. This is due to region coding, which is added to almost all DVDs to prevent the DVDs from being played by DVD players that were manufactured outside of the region. To play the DVD with region coding different from that of your Sony DVD player, you must unlock the unit and turn it into a region-free player.
Find the unlock code for your Sony DVD player model. The DVD Demystifiziert and Video Help websites both provide unlock codes for Sony players that can be unlocked and made region-free. To view the code for your DVD player, click on the model of your DVD player in the Sony hack list on the website.
Perform the tasks included in the unlock code. For most Sony models that can be unlocked, the unlock code is not as simple as pressing a few buttons. You may need to open the tray on the player or power the unit on and off multiple times as part of the hack.
Turn the unit off and then on again after you have entered your unlock code, even if the code doesn't include this step. Once you power the unit back on, it should be region-free and should be able to read any DVD that you insert in the tray.
Not all Sony players can be unlocked to be region-free. According to the DVD Demystifiziert page, no unlock codes are available for Sony models DVP-NC85H, DVX-11A, SLV-D980P and SLV-D500P.
Keep in mind that unlocking a Sony DVD player almost always voids the unit's warranty.