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Could I just throw a series of noninverting buffers on the /weout to introduce some propagation delay?

I threw together some VHDL to simulate the circuit design.  Does this behavior look correct?

So if I understand this right, during a CAS-before-RAS refresh cycle I want to keep WE high for some brief period after RAS drops low.  So I need to determine whether or not such a cycle is occurring, and then hold WE high.  Am I right in stating that the CAS-before-RAS cycle is the only time at...

So is it possible that UH7 on the SE/30 doing the same thing as the PALs on these SIMMs?  

So the crucial bit is only the section governing /o19?  That seems like it could be implemented by a couple of 74 series chips on a breadboard.  Looking at the Bomarc schematics for the II, which shares the same RAM system, each bank's /W is controlled by G7, a 74F240 inverting buffer.  But...

Nice, this might be helpful.  How did you generate that code from the GAL?

Theoretically, would it be possible to design a board that hooked straight to the address and data lines (perhaps by hijacking the FPU or ROM socket) and had all the memory muxing and refresh logic onboard, allowing use of any standard SIMMs, essentially bypassing the ones on the board?

The odd thing was it was working consistently with a MacSIMM, but after I swapped it out for a ROMinator II, neither worked consistently anymore. The only other problem I can think of is that the slot on the motherboard is damaged and does not hold SIMMs, forcing me to either use the rubber...

Turns out it wasn't stuck, it was just slow, and gives no indication it's making any progress (very little HD activity).  I left it for a couple of hours and came back to find it sitting at a repair confirmation prompt.  The A/UX installer had actually partitioned the drive to a 2GB volume...

Do you have an oscilloscope by any chance?  You could probe the green signal from the logic board, just to make sure the board is actually sending that green signal.

I have A/UX installed on a 4GB disk, which I recently found out is not a good idea since the Startup fsck can't fsck it.  But I really don't want to start over with a fresh A/UX installation.  At the moment the disk was unmounted dirty, but now it won't boot because the disk needs to be fscked...

Update:  It does seem to be the ROM.  I tried both a GGLabs MacSIMM and the ROMinator II -- both of them did the same thing.  Forcing a ROM checksum test from the debug interface reported a failure, as did a databus test at bit 1.  I swapped in the stock ROM, and that seems to boot reliably.  I...

I tried that.  But wouldn't bad ROM contact also stop the chime from playing?

It works sometimes, but is unstable, and upon a reboot, I'll get a garbled screen, as shown in the photo.  It does chime, but does not death chime (but the memory checks are probably being skipped due to the ROMinator II that's installed).  It seems to me like this is some sort of RAM issue, but...

Thanks, that would be great!  Although the icon in your graphic seems to be yet another version than the one in OP’s photo.

It looks like the ROMs out there are different from yours -- they have the normal blinking ? in a disk, not the symbol in one of your photos.

Good luck! Any idea if those ROMs are on the Web somewhere?

As someone mentioned, the ROM really needs to be preserved from this thing.  Do you know how to dump it? Have ROMs from either of the other two Twiggy Macs been dumped?

So Rhapsody has SWIM support but OS X Server 1.x doesn’t?

I'm trying to set up a headless machine I can download floppy images to, and then write them to disk using dd or equivalent.  I was planning to use a Beige G3 for this, since I figured it probably has the widest variety of OS choices.  Do any of the various NIXes out there (NetBSD, Linux...