Now I'm puzzled. Indeed, the service manual doesn't mention about HDD1830, i hadn't noticed that before, so in theory can actually be some hardware differences, but on the other hand, it worked before, so the player should not differ from each other.
Formatting a disk is a good idea, and if that does not work, then it must be a change that I made in the code in the period between the two versions. But it would be very strange for me, cause IIRC i haven't changed anything critical, except the LCD code.
EDIT:
I compared OF downloaded from the manufacturer's website for HDD1630 and HDD1830. Both files are exactly the same, which means that players should also be exactly the same. So I don't know really how is it possible that it works on mine DAP and it doesn't on yours. LCD code in OF is the same for both.