Very interesting, can't say I'm too surprised that they swapped for a circuit board based system in the 1990's as it was probably cheaper by then to use that than making the disc based mechanisms, which probably also rings true for most toys using similar systems as well (I was a child in the early 2000's and any sound emitting toys I had used microchip/IC based systems by then).
Been building Plarail worlds since 2001; Building when I can in 2023 