Yamada dvd5520 subtitles

[aceizace]

OK, i've posted this question to Umax, but the support from companys are usually slow and useless! Just incase someone here has had the same problem i thought i'd post it. Thanks. I have a problem with the DVD-5520 multi-region, i am trying to play dvds which are set to region 0, so they will play on all region dvd players. They play fine, however sometimes subtitles are required to translate japanese text on screen. When I turn the subtitles on, instead of the text a big white square takes up the whole/most of the screen. I have tried the dvds on other dvd players and the subtitles work fine, in fact the subtitles have worked on this dvd player for short periods, but then they go back to the white square. How can i fix this problem?