You have the old version of the K6 233. AMD used a design that worked well up to 200MHz at the usual 2.8V for split-voltage CPUs. To counter Intel's Pentium MMX 233, AMD selected K6 processors that ran stable at 233MHz if overvolted to 3.2V.

Your board might auto-detect that a split-voltage CPU is installed. Early socket-7 boards only supported 2.8V, or both 2.7 and 2.8V core voltage, but not 3.2V (for your processor) or 2.2V (used by the newer editions of the K6 and K6-3).

You have two choices: Either you find a way to force the board into single-voltage mode even though a split-voltage processor is installed (probably requires a bodge), make sure you are not using the VRE setting (3.45V), but the VR setting (3.3V), and overvolt even higher (3.3 instead 3.2), or you lower the multiplier from 3.5 to 3.0, and run the processor at 200 MHz. Most likely it will work without problems with 2.8V at that clock, and of course it runs a lot cooler at 200/2.8 than at 233/3.2. I don't expect 233/2.8 to work.

I've added a photo of the CPU. It seems to run stable for the moment as 233mhz at 2.8v.