Hi - Didn't see these messages earlier. Below are some things to consider - maybe with some repetition vs. my earlier posts.
The v1.27 ROM should work much better than that v1.11 ROM. Also, when you burn the ROM, assuming you verified it, it should be OK. Make sure you cover the window with a label to prevent stray UV erasing -- I'm sure you are aware, but mentioning it just in case.
It's remotely possible that the ROM could have a marginal/bad bit, but in that case, you could try to read-verify it a few times after you see the 100% reproducible problem to check that it hasn't changed. It wouldn't be my first worry if it verified.
The board should be able to support v1.27 -- SuperMac had to ship field upgrades to fix the Quark problem (see earlier posts). There may have been some changes to reduce rework. Maybe the earlier release boards had some jumpers on them down around the nubus connector -- I would have to look at the physical boards. As I may have mentioned in earlier posts, there were some timing changes to account for changes in the Xilinx parts in later boards - could have also rolled the board rev, possibly because of the Xilinx config ROM, but the declaration ROM should have been backward-compatible. The timing changes occurred towards the end of 1990 into early 1991, I think.
The Spectrum/24 PDQ is originally vintage 1990 with a final firmware upgrade in 1991 (v1.27). I think the SuperMac and RasterOps 19" 75Hz configs were present in the earlier ROMs -- so not something added just for v1.27. You have already figured that out based on what configs SuperVideo shows when using each ROM. Both v1.11 and v1.27 show RasterOps. The version of SuperVideo in 1990-ish would have been v2.07 or maybe v2.09, but v2.47/.49 should work. Beyond that, I don't know, as before.
The original Spectrum/24 PDQ preceded the Quadra 800. The fastest box available during original testing was probably the IIfx? There might have been some Quadra DVT testing with later ROMs and also testing on the released Quadra 700/900. However, the 900 had hardware/firmware issues that weren't fixed until the 950 came out. The 900 was its dirty little step-sister, but still a pretty good box for its era.
In terms of PRAM configs -- you shouldn't have to pull boards -- just zap PRAM on restart. Also, it doesn't require putting another board in the same slot. Just boot briefly with nothing in the slot or put the board in a different slot. It will automatically trigger Round Robin config.
If you want to debug this problem in a retro contemporary setting, start on a lower-end mac, like a II, IIcx or IIci with 6.0.8 and SuperVideo 2.0.7 as a baseline to see how it behaves (24-bit mode, assuming not using MODE32). If everything works as expected, then It might be possible that there is a 32-bit addressing gremlin somewhere (can't communicate, etc.). I think that error occurs when SuperVideo fails a call to get a resource from the board -- which could easily be an addressing error into boardspace. Also, I think the "can't communicate" error was associated with the custom programming feature in SuperVideo (which doesn't exist in Spectrum/24 PDQ). So, it could also be a SuperVideo software bug where it is doing something unexpected, leaping into hyperspace and hitting a dialog it shouldn't be hitting.
Once you profile the baseline config, you could then try using it in the Q800 in 24-bit addressing mode with System 7.1.2 as a test. Boot with a bare bones system. Also, make sure you have the correct system enabler for the Q800. I think that was back in the enabler days.
You don't need SuperVideo to set the video config (and acceleration should be on by default). So, you could boot without SuperVideo. Pull out any optional oscillators and just use Round Robin with the space bar at startup after zapping PRAM. What for it to sync on the 19" 75Hz config. As I mentioned earlier, I know that the 21" config was cable sense-based, but I don't recall if 19" 75Hz was or not. Maybe.
Another variable is the Shock INIT. The Spectrum/24 PDQ (and Spectrum/8 PDQ - a stripped 24) were the first boards that implemented SuperMac's VDI technology that allowed for external ROM patching. But, I think v1.27 ROM accounted for any interim external software patches.
Finally, there could be a hardware config/timing issue. The SuperMac SMT01 graphics controller was very touchy and could randomly bus error based on certain register timings (but usually when using Virtual Desktops). Seems unlikely based on what you describe...but maybe.
To help with debugging, if you are hanging at "Welcome to Macintosh," put in an appropriate version of Macsbug as the first extension that loads (root system level). It may not catch the problem...or it may. Might be interesting. You are hanging at the "Welcome to Macintosh" on the primary 13" screen, where the likely failure is when the OS tries to call Secondary Init on the Spectrum/24 PDQ before drawing the desktop (and that is also when the acceleration patches will be loaded).
And regarding baseline testing -- take out the other card(s) and just boot from PDQ as primary/only card installed. It sounds like there are too many variables in play. Also, in this single-card mode, then do 24/32-bit boot testing, etc. If it works in an older II box on a contemporary 1990-91 system (single/multiple boards, 24-bit/32-bit) and not on the 800, then it could just be a firmware or other bug because it was never tested on the Q800. I have all of these boxes and boards/ROMs. I don't know if my Q800 works, but maybe. Biggest issue at the moment is time. But, I hope the above helps.
