Which ICS clock chip does your board have (appears to be an ICS) ? IIRC if ICS9148 then only up to 66Mhz, if ICS9148B series or ICS9248 series then it can do 75Mhz....just going by memory.
Also JP6 is hardwired to from the pictures, it may have to be changed....

I will check the ICS chip when I am home this evening. My board is Rev D same as the color photo on Retroweb. I did not see a JP6 originally it has no pins and the board is still in its case this edge is beneath the optical drive I will need to investigate that maybe some surgery would be required.

The clock chip on this MB (DFI G586ITOX rev D) is an ICS 9169C. I found one refrence online that indicated it supports 50, 60 and 66 mhz only. It looks like I may be limited to 400mhz at 66x6with my K6-2+. I suppose I will focus on a variety of ISA sound options. With 2 pci+ 6 ISA (1 shared) I have started with a voodoo banshee, sb live, and Yamaha Isa card. The board seems very nice, it played a death march tune through the pc speaker when I forgot to plug in the CPU cooler fan.

Hi mistermister,

The ICS9169C does support the 75 and 83MHz clocks.

In the patched ITOXC_J1 BIOS I added x6.0 multiplier support for all possible FSB speeds, including the 6x75 and 6x83 setting. So the BIOS has you covered for these FSB overclock speeds. 😉

Cheers, Jan

Thank you for responding I may attempt to modify jumper setting of the unused JP6. The attached data sheet suggests this may work I presume JP6 corresponds to FS2 which when set to "1" enables 55,75,83 FSB options whereas "0" , the current position which is hard wired, enables 50,60,66 which are currently available. There is also interestingly a position which appears to allow an external clock which currently does not post probably no clock is connected. I suppose one would need to attach a clock directly to the chip to attempt this. I may not get to all this right away but thanks again for the information and all you bios work I am using your modded bios in multiple builds. I posted a long time ago about a bios I would like to see for a compaq k6+ compatible machine maybe I will revive that post again soon.

Upon further reading of the data sheet it appears this clock chip can run the pci bus asynchronously at 32mhz, independent of the FSB, or the more typical fsb/2. Is there a simple way to tell what frequency the pci clock is running at?