I had a spare Japanese Megadrive model 1, which I needed to convert to 50Hz / ENG so I could play Prince of Persia (UK version) as it is region locked. Done the mod but if the machine is running at 50Hz it lacks sound, however boot in 50Hz and drop it into 60Hz and the sound does play (not straight away but at certain points but it sounds much too fast), however other non region locked Japanese games (Sokoban, Sonic) do play the sound in 50Hz so I am a little confused. The game does play sound in 50Hz as a UK Megadrive Model 2 works fine. The model is a MD5 VA7 which I believe is the last revision of the Megadrive 1 which has the single Sega custom and the sqaure 68000 chip. Anyone have any ideas to get the sound to play at 50Hz?
It is the UK version of the game, so if you run it in 60Hz you get a "This game is for PAL and SECAM regions, blah blah" and there it freezes. Run it in 50Hz and there is bugger all sound, switching to 60Hz in game will get the sound back but it's too fast, drop back to 50Hz and it goes away again. The VA5 model I have does not have this issue :s
Are you sure it's running at 50hz (i.e do you have larger vertical borders on TV display) ? I mean, there are actually two signals that are used to change the console region: NTSC & JAP. The thing is, the first one is also used by the VDP chip so, depending on the model you have, you might have only modded the I/O chip (which game are essentially reading to figure console region) and not the VDP chip which is still using NTSC timings, causing compatibility issue (no sound is often related to Z80 interrupt timings issue)
The Eng / Jap switch does basically nothing for Prince of Persia, it seems to ignore it. But yes it is switching to 50Hz with the JP3 JP4 jumpers, no sound in 50Hz and sound in 60Hz if switched whilst running. I do not have that many games to test but Sonic, Sokoban and TFIV all work fine in both speeds on the VA7 machine but PoP seems to lack sound in 50Hz but works fine on a VA5 machine...
