Minimum Boot (Macintosh SE/30)

if you are having issues with your macintosh se/30 not working correctly or at all, i like to start with the absolute minimum requirements for boot to rule out as many items as possible that could be faulty we will start by booting the main motherboard from bench without any monitor, audio, analog board or anything else at all this will allow us to test the motherboard itself this is the motherboard (note this is a reloaded not original pcb, and various components not yet installed, but it looks very similar to the original) power rails attempting to power up the motherboard on its own with just a bench power supply and minimum rails, using an oscilloscope to see video output 12v rail (j12 pin 14) goes to external and internal drives, external pds connector and sound, so will boot without 12v to some degree, however the sound chip ub11 will hold the system in reset so you will only get to horizontal lines/simasimac screen at most j6 (external 3 5" floppy drive) j8 (internal floppy drive) j13 (pds video/expansion slot) ub10/ ub11 /ua9 (sound) 12v rail (j12 pin 7) goes to the pds slot only, so should definitely boot without it j13 (pds video/expansion slot) 5v rail (j12 pin 6) goes to the line drivers for the printer and modem, and the pds port, so again should at least boot without it ue12 / ud12 (line drivers for printer and modem) j13 (pds video/expansion slot) this leaves the 5v rail (j12 pin 12/13) which goes everywhere else to loads of logic this is absolutely needed based on that, the system should at least boot with some video output on j12 (pins 9/10/11) we can observe with an oscilloscope with just the motherboard and 5v rail powered however, due to ub11 sound chip not having power it will hold the !reset line at 2 5v getting to horizontal lines/simasimac screen at most to get to a further boot, you need to also apply the 12v rail power from bench based on the information above it should mean we can boot to horizontal lines/simasimac screen with just 5v power applying ground and 5v on j12 like so on applying power i get 1 6a of current draw and 3v peak to peak signals on the vsync (j12 pin 11), hsync (j12 pin 10) and video (j12 pin 9) if you have it i would also apply the 12v power too so you get audio and it can come out of reset system clocks it is best to check the crystals are operating as nothing on the board will generally work without them using an oscilloscope check the crystal closest to the rom (front right) which should be 32 77khz sine wave with the top pad being a little more square it should be around 3v to 4v peak to peak the same for the crystal close to the powe connector, it should be 16 93mhz and 5v peak to peak (if your scope isn't quick enough to measure it well it might appear lower peak) !reset line several chips can be held in reset or control the reset of other chips although the video output circuit works regardless of the state of the reset line (so you can see the horizontal lines/simasimac) the system won't do anything useful until out of reset the reset line connects to 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 this is what a system typically held in reset (or with other faults preventing initial post/boot) would look like this is with tms 4461 ram with other ram the visually is typically look like this without ue7, ug7, ug6 and video ram will still boot with audio all of them are needed for video with ue7 missing you will get video but white screen