Retro ViatorDo any Mac repair aficionados know what pin 16 on both Sony sound chips in the Mac IIsi connect to? The BOMARC schematics show it going off page to a page I don't have.
Giovanni - ZL2GX@RetroViator You'll probably have more luck if you add some hash tags. Then you post will pop (as I understand it) in those on other servers - not just mastodon.social.
Daniel Tufvesson@RetroViator I believe these are the "TEST" inputs to the sound chips. Normally left unconnected or routed to a test point.
BigBadBiologist@RetroViator Something interesting is that the SE/30 has them going to pins 29 and 30 of the ASC (improperly labeled in the schematic as OSC). Those two pins are accounted for in the IIsi. Are 14, 16, and 18 all connected on the chip?
@BigBadBiologist @RetroViator We need to be careful here since the sony/sound chips of the SE/30 and the IIsi uses different packaging. Pin numbering is different.
@danieltufvesson @BigBadBiologist
It's a great idea to compare with other systems--even with pin differences, because I should be able to see what's missing.
I'm working on comparing the audio circuit schematics of IIsi, IIci, and SE/30. It is driving me a bit batty, but it should be helpful.
@RetroViator @BigBadBiologist It may be a good idea to look at the IIcx as well since it’s basically an SE/30 with Nubus
Khleedril@RetroViator Just idly curious, but, are there any loudspeakers in the system?
Justin Derrick
Michael Engel
DosFox@me_ @RetroViator ah looks like they go to a test point.
If PWM in, audio out, SV0-2, POR, the reset switch and the power rails are accounted for - it's likely just a test point
Thanks. The pin probes out as a 22.5KHz clock signal, but at a lower amplitude than that found on pin 18.
The reason I think I'm missing a page, aside for the lack of a sheet marked with a "Left" alignment marker, is this photo of an original set posted on 68kMLA (zoomed in to the relevant sheets).
@RetroViator @DosFox Here's a better picture (from https://68kmla.org/bb/threads/reverse-engineering-the-macintosh-iisi-logic-board.39950/). Pin 16 of UB7/UB8 is connected to the output of what I think is a comparator (UA10).
