MCD Region free bios won't boot

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Hi everyone,

I have repaired an early JAP sega mega-cd. It works just great now, but it still has the original bios (EPR-14563H) I have used my trusty old willem programmer to program a 27c1024 with a region free bios from l_oliveira but it doesn't boot.

I have verified it multiple times and looks like it is programmed correctly.
I programmed 3 other 27c1024 with other bioses PAL, USA and an original JAP, still nothing
I then tried some other eproms.
I tried reading the original bios and it doesn't have the usual sega header.
by that time.... 🤯

So I guess I'm stuck with converting all my cd's over to JAP region.....

To verify my programmer still works I programmed a 27c322 with Sonic 3 complete and I can play the game just fine.... I am at a total loss at what is going wrong... any help would be very much appreciated.
 
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Doesn't the bios requires byte swapping?
 
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That's probs why then give it a try
Thanks for the bump[, but that's not the problem. I know this for sure because I did a byte swap, it's the first thing you do after you load a bin-file. The problem is more likely to be with the software or the 40pin adapter I'm using.

I did find another forum where somebody had the same problem, no solution though; MCUmall
 
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I can send you a region free bios preprogrammed if you like .
 
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That would be really nice! I did find somebody with an eprom burner so I try that first and if that doesn't work out I will surely send you a DM.
 
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That would be really nice! I did find somebody with an eprom burner so I try that first and if that doesn't work out I will surely send you a DM.
no worries i noticed not everyone from ag games has moved here yet
 
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