Yeah it was me that first raised it as a solution on 68kmla (I never saw it anywhere before, but I mean, apple engineers knew and someone else might have spotted it if they were familiar with the 88916 and beeped around the chip). My machines were always stable at 33MHz so I hadn't needed to make the change, but other people were having issues so I suggested making the swap to change the SCSI clock. I later made the change myself when I started pushing to 40 and 50MHz and beyond. Around that time I'd spent a load of time mapping out the Q610 timing settings and clock circuit, the LC475 is similar, but doesn't have independent footprints for a separate clock for ethernet and SCSI like the 610 does (the second clock isn't fitted on some machine configs).
Not entirely, soft power (on machines that have it) isn't just part of ADB. It actually goes to the Nubus, can be controlled from software and on some machines even goes to the IR port control board (which has another of the same type of MCU).
No modern equivalent, but thousands of NOS and recovered parts available cheap. If I was doing a repair or a reloaded board, I'd always stick the DW80 on it for the couple of dollars it costs as they're completely compatible and give the possibility of pushing beyond 40MHz. The stock part actually seems to be the first hard limit on overclocking, without replacing it people seem to get between 38 and 42MHz. Some of us are getting up to about 53MHz with the DW80.
My poor Performa 475 was a rescue
. This was my video circuit! If I remember, the main issue on this one was the 31.3344MHz clock was dead, and there was some issues in the sound circuit, plus the usual recap. On, and a resistor had got hot and broken, I assume it developed a short.
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