Realtek 8029, 8139 and older 3Com 3c905 caused trouble on my 40 MHz bus, but I found that later 3Com cards (3c905c, those with the small PCB) work fine so far.

I may have different findings than you concerning later 3Com PCI cards. Anything besides a 3Com? Are those 2001-era Linksys cards CPU hogs?

YMMV, of course. 😉 After all, I only tested about five cards until I found one that worked on the overclocked bus, and there are a lot of 3c905 variants.

Which variant are you using?

I have two 3c905c-tx-m, an older one made in the USA, and a newer one made in mexico. I also have a 3c905B that looks similar to the 3c905c without the boot rom.

The 3Com 3C905C has now been working at 40 MHz for the past 24 hours. Randomness? Dumb Luck? Vintage karma?

w00t?

I have two identical 3c905c-tx-m "Made in Ireland". One is in my 486, the other in my Athlon box. Both tolerate a 40 MHz PCI clock. There is just one problem with these: They have an awful SMD-mounted RJ45 jack which tends to break if not handled with care.

To complete my findings, it was likely the re-arrangement of the PCI cards that seemed to enable safe 40 MHz operation. The trio includes an Adaptec 2940U2W, 3Com 3C905C-TX-M, and a Matrox G200. A 6.5 cfm fan was also added to the Matrox's heatsink.

I've heard that Adaptecs are not very tolerant to PCI overclocking...

iulianv wrote:

I've heard that Adaptecs are not very tolerant to PCI overclocking...

I heard this also, and even if it works in a standalone rig, you only know for sure it works if you've tried networking it with other computers.