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PDf[31:0] at U8 in the Quadra 800 schematics? https://68kmla.org/bb/index.php?threads/centris-quadra-650-800-behaviour-when-leds-are-fitted.46961/post-525870 If it's not the traces, then it could be U8 itself?

I would have to look at a schematic to know the actual names of the signals/traces. Can you take a screenshot? If the problem is not captured in the screen shot, then the problem is not between the CPU and the VRAM or in the VRAM - it is between the VRAM and the display output.

Color fringing seems excessive. A white horizontal line should ideally not have color fringing at either end (unless a line or bit exists within 2 bits of the edge of the line), though I don't know if that's possible with analog circuitry or simulation. The output of the Apple II is digital...

Does this GPU have a black and white mode? That may help identify what bits or bytes or words are bad.

The B&W image indicates a 32-bit bus with D29 or D28 being stuck low.

What is 28F020 command 30h? I don't see it in the Intel or AMD data sheets. Do flashable ROM SIMMs have extra logic to catch this command?

What color depth is being used in the photo? Change it to B&W so we can see which VRAM data lines are broken.

Did Apple reverse the order of the data bits for 8 of the 16 Am28F020 chips? i.e. D0-D7 -> D7 D0?

"Flasher (TNT 0.6)" expects AMD 28F020 (vendor/ID = 01,2A) or Intel 28F020 (vendor/ID = 89,BD). Since these chips are 2 Mb there are 16 chips = 4 MiB. 8 chips are accessed using 8 bytes at ROM base + 0 (1 byte per chip). The other 8 chips are accessed using 8 bytes at ROM base + 2 MiB (1 byte...

Working on porting B&W G3 Firmware update to ANS/TNT Open Firmware. I'll try making DingusPPC emulate flashable ROM to test that and to see "Flasher (TNT 0.6)" work to completion.

Should perform a test in DPPC to see if anything (exception handlers?) in ROM is accessed after Open Firmware is set-up. Can do a copy to RAM and virtual memory to compensate maybe.

The closest thing would be the 8100 schematics. https://www.macdat.net/repair/apple_schematics.html The 6100 and 6100 Enhanced Developer Notes mention Cuda but not Egret https://leopard-adc.pepas.com/documentation/Hardware/hardware2.html

Can a ROM SIMM be created that has a switch to switch between two different ROMs while the Power Mac is running? The first ROM would be a working ROM to boot into Open Firmware. The second ROM would be the target for flashing. Boot the first ROM into Open Firmware, then flick the switch to...

The name of the ROM Flashing Utility is "Flasher (TNT 0.6)". I ran it in DingusPPC emulating a Power Mac 9600 v1. DingusPPC shows the code below after setting the RomWE bit of the ROM Timing Register. It uses 8 byte read/writes to FFC00000 and FFE00000 to probe the ROM (offset 0 and offset 2...

They are usually unnecessary, since the default conversion radix is sixteen. Alternatively, you could use hex ffc00000 400000 dump Check the current conversion radix with this: base @ .d If the conversion radix is not 16, then ffc00000 cannot be interpreted, causing the remainder of the command...

The ROMs I've uploaded the 3 new ANS ROMs to https://github.com/joevt/MacROMan There's 4 total now. They are similar to the Power Mac 9500 v2 ROM. In fact, the 2.26B6 ROM has identical first 3 MiB. 077d.28f2.1 9630c68b 045a3ff2.04a8169b.03334745.03ffe575...

According to the checksums (and doing a binary compare) the broken last ROM is identical to the first new ROM that we received (2.26b6) except for the byte 2 lane errors in the first 2 MiB of the ROM so I don't think we need to try and fix it. The broken ROM was able to get into Open Firmware...

I will post ROMs to my MacROMan fork and add some notes here later. The last ROM we're working on has problems. It has errors in byte lane 2 (8 lanes numbered 0 to 7). Byte lane 2 is the address with least significant bits = 010. 077d.28f2.1 "Boot TNT 0.1p..]" 4096 9630c68b...

Also useful would be a dump of the PCI registers of all the PCI devices since dump-device-tree shows only some of them. Here's a dropbox link with the required script for Open Firmware...

The serial cable should be a null modem cable, such as what you would use to connect a printer, like an Image Writer II serial cable. The receive at one end should connect to the transmit at the other end. Zip the captured text and attach to a post.