This is a very fine Baby-AT Socket 7 mainboard!

First are you running the latest BIOS that supports all the late K6-III CPUs?
Second the K6-III is quite a powerhungry CPU and it´s power consumption rises with the frequency. If the electrolytics besides the CPU in the VRM circuitry (about 7 of them where the two toroidal inductors are) are degraded (which might well be) the necessary voltage will non longer be reached or will have too much ripple. In this case the system wouldn´t start either. If you have a decent voltmeter you can measure the core voltage at startup to verify it´s really stable at 2.5V exactly.
You can measure it at one leg of the left inductor.

Btw. I seriously doubt you can overclock a regular K6-III to 600MHz, I´m not even sure every 450 MHz sample can do 500MHz or every 400MHz sample can reach 450 MHz let alone more.
For overclocking you should buy a K6-3+ (400 MHz or higher).
Edit: bloodem just pointed that out while I was typing and I agree 100%.

nuno14272 wrote on 2023-01-27, 11:45:

Hello fellows, […]
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Hello fellows,

I have this babyAT board (DFI P5BV3+) with a K6-III 400mhz and i was trying to do some overclocking. At least put the cpu at 500mhz wich is my goal.
I know is not a "recent" board but i've read some good reaviews about this board. (Have other like the FIC PA2013)
I think the K6-III have unlocked multiplier right.
So, i set the board jumpers to 100fsb x 4multi and everything is fine
them i set 100fsb x 4.5 multi and i get a K6-III 450mhz - great.
then i rise the voltage to 2.5v (original is a 2,4cpu) and set to 100fsb X 5 multi and the computor does not boot.
I mean.. i see all this people getting 500mhz/550mhz, even 600mhz easy and it seams i cant get past de 4,5 multiplier...on this board.
strange..

I think you are confusing the K6-3 Plus CPUs with the normal, non-plus K6-3. If you have a non-plus CPU (and you do, since you mentioned that the original voltage is 2.4), then you can forget about reaching 500 MHz... I've never seen one that can do it (at leaast not @ reasonable voltages).
On the other hand, most K6-2+ / K6-3+ CPUs can easily reach 550 MHz.

Yes, is not the "+".. is the plain K6-III 400mhz

I've tried this cpu in another board ..the FIC PA2013, either with multi 5x, and with 4,5x multi and 112mhz fsb and it's a no go.

The computer doesnt boot. so. my conclusion is

This k6-III is not a good overclocker.. 450mhz is what i can get only and that's it.

Well.. it is what it is...