the Commodore folks solved this on their '040 Amiga CPU card by using a raft of ten (10) GALs, which burned a ton of power.
Top-level
the Commodore folks solved this on their '040 Amiga CPU card by using a raft of ten (10) GALs, which burned a ton of power. 23 comments
@tubetime This post suggests power management. https://68kmla.org/bb/index.php?threads/where-to-find-341s0851-c-1990-apple-lciii-boot-issues.37152/ @tubetime that's 343S0120, often found alongside the customized 68HC05 Apple calls Egret (Cuda in later models) used for ADB, housekeeping tasks, PRAM, reset (and NMI) management, etc. IIRC '0120 serves as a power monitor, switching the HC05 to battery power when system power is cut. ...as seen here on a 630 DOS/LC580 board. i removed the 'ls125. there was definitely a puddle of electrolyte underneath (it crackled and fizzed during desoldering). note that the potentiometer connection (red arrow) is right next to a pin tied to ground (blue arrow). electrolyte is conductive, so maybe it was creating a leakage current.
[DATA EXPUNGED]
@tubetime Did you figure out what the ‘LS125 is doing there? I looked it up and guess it’s just a buffer. https://www.ti.com/lit/ds/symlink/sn54ls125a.pdf @tubetime Ahhh, so IBM _wasn't_ the only company that used an RC circuit as an integrating ADC :'D! @tubetime I feel like that's the spiritual successor of the SE's BBU which turned a half dozen or so PALs into a single chip |
the one thing i haven't figured out is this chip.