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The pre-FDHD ROMs for the Mac II will fail if they see more than 8 MB of RAM. MODE32 can only help you if the system can boot in the first place.

The FDHD ROMs are required for RAM sizing to work properly above 8 MB. You don't need the actual SWIM floppy controller and SuperDrive.

The IIgs RGB monitors are prone to cold solder joints on the flyback transformer. I've had to reflow mine every so often to keep it from doing that flickery thing. If you give the monitor a firm thump and it changes the flickering, even briefly, that's probably what's happening.

Yes, the microcontroller is an extended 6502. Mitsubishi calls the architecture "MELPS 740" or "740 Series", there's good documentation here: https://bitsavers.org/components/mitsubishi/melps/

Hi chip, the latest version of MAME (https://mamedev.org/) supports the Portable, PowerBook 100, PowerBook 140, PowerBook 145, PowerBook 160, PowerBook 165, PowerBook 165c, PowerBook 170, PowerBook 180, and PowerBook 180c. All machines correctly identify with the right BoxFlags and Gestalt...

The Classic II ROM will detect an FPU and use it for SANE.

If there's no shorts on any of the rails, it's likely something is drawing excessive current, probably due to a near-short. Check the components connected to the SCSI port (the 5380 main SCSI chip being a likely suspect) and look for signs of the magic smoke having escaped.

Ooh, interesting!

The FAS parts are generally enhanced clones of the NCR538x and 539x chips. This card is either A/ROSE-based or similar, which doesn't strike me as the friendliest reverse-engineering candidate, but you never know.

31.3344MHz is an important clock in 68K Macs. It's 4 times the original Mac 128/512/Plus clock, 2 times the Mac II/IIx/IIcx/SE30 clock, and so on. Lots of other chips like IWM/SWIM and the VIA used clocks derived from that as well. As a wild guess, it's used to slow the 601 down to match...

Yes. I've attached the SE/30 schematic. The first page has the PDS slot. Pins 4, 44, and 84 are the 3 Interrupt ReQuests (IRQs). Slot pin 84 (IRQ1) should have continuity to pin 2 of the chip at UK11 (page 4 of the PDF). Pin 44 (IRQ2) should have continuity to pin 3 of UK11, and pin 4 on...

This is the kind of reverse engineering most emulators have to do, because there is usually no way to read the PLDs/FPGAs, and the custom ICs are black boxes. The 32K RAM window is probably mapped at 0xFFFF8000 on the x86 side since the 386+ boots at 0xFFFFFFF0. If 0xFs040000 is written after...

Dragging the menu bar to set the primary monitor has been a built-in MacOS feature for as long as it's had multiple monitor support.

Check continuity on the PDS interrupt pins back to, I believe, VIA2. The Xceed card's interrupts aren't being received. Nothing to do with the analog board.

The boot chime does wait forever on certain status bits from the ASC so it can work "by accident" due to stray bus capacitance, but I wouldn't rely on it.

Might be a small PROM with the ID rather than an EPROM. The chip above the crystal on the left side of the card has the markings mostly smeared out but it looks like it was stamped "ROM". ...and then I see the other, clearer picture and it's just a 7400 and "ROK", not "ROM".

With the amount of corrosion you can see underneath the pins it'd probably be a good idea to just remove the entire chip from the PCB and give it a good cleaning underneath.

MAME supports almost every desktop 680x0 Mac now except the Quadra AVs, with the original ROMs and emulating the actual chips. Is there some test I could run on the emulated IIsi for you?

The first-gen PowerMacs supported 2, 4, 8, 16, and thousands of colors on their motherboard video (which is actually borrowed from the LC III).

Bright line in the middle isn't lack of sync, it's lack of vertical drive. Gonna be something on the analog board.