Very Minimal Boot (Macintosh SE/30)

if you have a major issue like no bus activity, no boot sound, or even no av out, it is best to start with the absolute minimal boot, and look for the address bus toggling constantly on power up, or the initial boot audio chime critical ics the initial startup is done by the glue logic chip ui8 i have not fully reverse engineered its boot up yet but have found all required chips the following ics are critical for the boot operation of the system to get to the out of reset address toggling state 68030 cpu (uk8) glue logic (ui8) pal for ram signals (uh7) pal for 68k/video signals (ui6) resistor packs for pull ups (rp7 / rp9) sound ic (ue10) rom (j14) if we want to hear boot sounds, if not oscilloscope for address bus activity below are the critical ics with a pink dot (plus the ue10 sound chip above and to the left of these) now to boot from only 5v we want to remove the sound chips too and with up the headphone port so we can still hear audio from the headphones remove ub10 / ub11 jumper between ub11 pins 8 and 9 to short together analog and digital grounds (audio will be a little noisy) this also makes the s2 nmi button work again as once ub11 is removed the analog and digital grounds are separated and the reset button uses the disconnected ground note s1 normal reset button won't work with ub10 removed as it is responsible for sensing that button and pulling reset low so use s2 or disconnect power to reset non essential ics you can remove all non essential chips in case them failing pulls voltage rails or lines bad if you are still struggling to diagnose ud1 uk4 (rtc) ud12 / ue12 / ug12 / ui12 uk12 / uj11 / uk11 / ul11 ui5 (fpu) all ram (because if it successfully checks ram but ug12/ui12 or uj11 fail or are missing you won't hear any beep and get horizontal lines) uk6 (video ic) ue6 / ug6 / ue7 / ug7 (pals) uc6 / uc7 (video ram) ua8 / ub8 / uc8 / ud8 / ue8 / uf8 / ug8 ui2 / uj2 / ui3 / uj3 / uj4 / ui4 / uj6 (logic) rp1 / rp4 / rp5 / rp6 / rp8 (resistor packs) expected boot with just the critical ics installed, if you have also removed the sound chip and bridged the audio jack (otherwise if not you will need 12v power applied also) you should expect to hear a sad mac boot sound when power is applied if you have no rom, instead you can probe the lower address pins of the rom socket and they should be constantly pulsing if you do not see this, perhaps check all the following chips happy to come out of reset in/out 68030 ( uk8 ) !reset via1 ( uk12 ) pin 37 via2 ( uk11 ) pin 37 apple desktop bus adb chip ( ul11 ) pin 4 (for keyboard/mouse) super woz integrated machine swim ( uj11 ) pin 25 (for floppy drive) 53c80 scsi controller ( ui12 ) pin 7 (for hdd) asc stereo sound chip ( ue10 ) pin 40 sony sound chip ( ub11 ) pin 5 any or all of these chips can cause the !reset to not go high even if they are inputs as if they go faulty it could pull the pin lower