By mistake, my matshita uj-8505 was changed to region 3. How to change the dvd region back to 0?
I don't believe there is a region 0. DVD regions are numbered 1 through 8. Anyway, open up Device Manager, expand the DVD/CD-ROM arrow and double click your drive. Select the DVD Region tab and pick your country from the list. Keep in mind that the number of changes you make is limited. When you're out of changes the drive will be locked. The number of changes left is shown in the dialog.
Region 0 = Region ignored, problem is that windows/software will not normally let you apply a region 0. Only way I know is thru "3rd party" Firmware updates. This was primarily aimed at stand-along DVD recorders. I used this 3rd party Firmware to add 3 hr record mode to an old Lite-on DVD recorder for recording TV to watch latter., While it made no diff to me, it also set the drive as region free. Have not followed this for several years as PVR are more available and also newer DVD DL stand-alone recorders..