I’ve done the mod myself - the info is at http://hardsdisk.net/1400clock.html . Can confirm it works 100%.Interesting, I did not! Well I've got a 166 board so I'm good for now, but that is good to know. Do you know where I could find resources on downclocking? Would be a good page for my website. I wonder why it doesn't work at 166 though, Newer, Sonnet, Interware, etc, managed to get G3s working on the 117/133 boards no problem. Would love to know the technical explanation behind that if anyone does know.
The issue is the ROMs on the 117MHz board - they do not support/recognise multipliers above 4x, so the maximum setting is 133MHz on a 33MHz bus. Obviously the upgrade card manufacturers found a way around this, perhaps they patched the ROM at startup?
The only difference between the two revisions of motherboard is the version of the ROM chips onboard, the later one supporting multipliers of 5x and beyond. That said, I doubt you’d see much difference between a 133 and 166 in real world use, it’s having the 128kb L2 cache that really matters.