> Apparently some of the bootlegs of both this and Phoenix used different doorbell
> chips too?
There is a Atari Tetris bootleg that uses an additional Z80 and a UM3482 for sound (a doorbell chip).
Sean decapped my UM3482 and the bits are clearly visible, but we cannot make sense of them (we cannot find the logical order). There is no CPU core on it, and there are four ROM regions, one for notes, other for the offset of each doorbell melody and the other two are for unknown purpose.
Sean even captured the output of the chip with a logic analyzer while it played all 12 songs, then wrote a program to measure the period of each note and count the number of cycles it was played... But still we're missing something.
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