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Use the twist method to remove caps rather than hot air. Your yellow circled vias look correct to me.

Won’t it just recognise it as a 256MB module due to chip density?

Looking back at this bit of my copied code, it looks like I typed in a bunch of commands in the middle of a device listing. I could have sworn that I never did this - instead, it asked me to press spacebar to continue showing the listing. I'll need to double check but I'm in a bit of a rush at...

Yeah I got a bit confused about the pasting process without any feedback. I tried again just now and I think I managed better. Open Firmware, 2.4 To continue booting the MacOS type: BYE<return> To continue booting from the default boot device type: BOOT<return> For Open Firmware serial I/O...

Absolutely. Reverse engineering a 1400 Series G3 accelerator is the way to go here. The 1400 Series *is* a 500 series in fancier clothing. 500, 190, 5300, 2300, 1400... they're all the same basic architecture. BTW, you mean PBX, rather than TREX - the bus translator/memory controller?

The mods that have been done so far have been superficial in the sense that no attempts (that I know of) have been made to use for example a logic analyser to understand where in the boot process things are hanging up and why. This is not to play down the importance of the work that has been...

I don’t agree it’s ‘not meant to happen’ - it could just be something marginal that needs adjusting to get it going. I’m of the opinion that someone could get this working if they were dedicated and capable enough. Many feats have been accomplished in the community which were previously deemed...

I pasted in your code successfully and it does seem to successfully modify the device tree, but the end result is that the floppy drive still doesn't work. Here's my output: Open Firmware, 2.4 To continue booting the MacOS type: BYE<return> To continue booting from the default boot device...

dev / ls in OF lists the swim3 controller, not the mfdc... interesting

I grounded the Disk In Place and Media Density Select pins so that the Mac thinks theres always a high density disk inserted, but this didn't change anything. Interestingly those pins (4+6) do go back to the controller IC on the floppy drive. Pin 4 is connected through a solder jumper labelled...

OK, the LPX-40 dev note (thanks @finkmac) gives us some clues: So, auto-eject MFM drives exist, but sounds like it could be an optional feature here. Right, so the Mac is looking for a Disk In Place signal - you can see that on the Gossamer schematics labelled MFDC_DIP_I. But regular PC...

So I discovered my floppy drive has DS0 and DS1 solder pads on the PCB, and I moved the solder blob over. I do now get signs of life - the floppy drive indicator light comes on with the Mac's power light, and then stays on until the grey screen with mouse pointer. Just before the Mac starts to...

The schematics show that only drive B is supported - but the twist in my floppy cable sets mine as drive A. I'll try a cable without a twist.

Thanks for clarifying this. EDIT: 'Disk change' is pin 34 on an MFM drive, which is labelled 'no connect' on the Gossamer schematics – so that couldn't work.

Well done!

Looks to me like one of the VRAM chips isn’t being written to correctly and is displaying uninitialized data.

It might be firmware related. I don’t quite get how a PC floppy drive would have integrated with Mac OS, though. Normally, when you insert a disk it appears on the desktop - but afaik a PC floppy drive doesn’t have any way to signal to the OS that a disk has been inserted.

380W. The original is a 200W but it has a beefier 5V rail (30A) than the Antec (20A), which is the important thing here.

So I have now, and it doesn't work. No sign of life. Of course I made sure the floppy cable was the right way round and that the drive was plugged into power. I also swapped in a Rev. A ROM and booted Mac OS 8.0 just in case the newer ROM/OS had dropped support for it. Interestingly theres a...

Only one way to find out…