I would guess the issue is that the Soyo SY6BA+only supplies 2.0V to the CPU which is in range for the Katmai PIII 550, but out of range for the Coppermine PIII 700 (1.6-1.7v).

In terms of getting the 550 running at full speed, you just need to set the system bus speed (FSB) to 100Mhz in the bios settings. If the system is not POSTing at 100mhz, maybe the RAM is not working at that speed

According to this thread, the VRM system on the 440BX is entirely done in hardware using a single chip, so you can replace one chip on the board to upgrade it to coppermine voltage support:
P3 Coppermine Voltage in GA-6BXC Rev 2.0 Mobo

550 not being able to be set to 100Hz fsb mighty also be power supply or motherboard capacitors near slot1
that 700 mhz Pentium 3 is slot1 or in a slotket?
Intel VRM 8.1 and 8.2 standards only guarantee 1.8-3.5V support https://kentie.net/article/deskproupgrade/vrm8.2.pdf
VRM 8.4 Introduced Coppermine support and goes down to 1.3V https://kentie.net/article/deskproupgrade/vrm8.4.pdf
Common trick is using a slotket with VID pins and bumping Vcore from standard 1.7-1.75 to 1.8V. Anything below or equal to 1.9V is harmless for Coppermine CPUs.
There are also ways of modding slot1 cpu or slotket without jumpers to make the motherbaord think an 1.8V CPU is installed.

NeoG_ wrote on 2026-03-24, 08:55:

I would guess the issue is that the Soyo SY6BA+only supplies 2.0V to the CPU which is in range for the Katmai PIII 550, but out […]
Show full quote

I would guess the issue is that the Soyo SY6BA+only supplies 2.0V to the CPU which is in range for the Katmai PIII 550, but out of range for the Coppermine PIII 700 (1.6-1.7v).

In terms of getting the 550 running at full speed, you just need to set the system bus speed (FSB) to 100Mhz in the bios settings. If the system is not POSTing at 100mhz, maybe the RAM is not working at that speed

According to this thread, the VRM system on the 440BX is entirely done in hardware using a single chip, so you can replace one chip on the board to upgrade it to coppermine voltage support:
P3 Coppermine Voltage in GA-6BXC Rev 2.0 Mobo

Do you know which chip that is specifically? And if so, is it something that is socketed or would I have to solder it onto the board?

soldering involved, or if the chip is in a slotket just change jumper setting
but first you would need to solve mobo crashing after setting 100MHz - that is a big problem

There is some old online chatter that only revision E boards with BIOS 2CA7 or later can support slot 1 coppermines or, failing that, you'd need to use a slocket / skt 370 combo with voltage clamp / jumpers set to 1.8V. The board revision should be marked on the underside corner near the ISA slots

I would try and resolve the 66/100mhz bus speed issue and then tackle the VRM issue second.
You mention wanting to run Windows 95, nothing wrong with that but might need a patch for either of those CPUS depending on which version of Windows 95 you are running.
What are you wanting to use the PC for specifically, games? If so, which games as a Pentium III class system is pretty overkill for most any Win95 era games.

Jasin Natael wrote on 2026-03-24, 13:14:

I would try and resolve the 66/100mhz bus speed issue and then tackle the VRM issue second.
You mention wanting to run Windows 95, nothing wrong with that but might need a patch for either of those CPUS depending on which version of Windows 95 you are running.
What are you wanting to use the PC for specifically, games? If so, which games as a Pentium III class system is pretty overkill for most any Win95 era games.

In the BIOS there is an option to change the clock speed under the "Soyo combo feature" menu, but every time I try to enter that menu the machine locks up on me, and trying to navigate the menu with the keyboard causes strange beeping to come from the PC speaker. Any idea what that's about or how to fix it?

rasz_pl wrote on 2026-03-24, 09:29:

soldering involved, or if the chip is in a slotket just change jumper setting
but first you would need to solve mobo crashing after setting 100MHz - that is a big problem

It crashes before I can even set it back to 100mhz, as soon as I enter the menu to change the clock speed which is called the "Soyo combo features" menu, it locks up on me and I just get some strange beeps from the speaker every time I press a key on the keyboard.

Sounds like faulty MB. It shouldn't freeze in BIOS setup. To be absolutely sure you would need another 100FSB CPU or another 440BX board.

AlexZ wrote on 2026-03-24, 16:13:

Sounds like faulty MB. It shouldn't freeze in BIOS setup. To be absolutely sure you would need another 100FSB CPU or another 440BX board.

I do have another 100mhz cpu, a Pentium 2 that clocks at 133mhz and it still freezes on me in the Soyo combo features menu. Is my motherboard just screwed at this point?

bunghole102 wrote on 2026-03-24, 16:18:

AlexZ wrote on 2026-03-24, 16:13:

Sounds like faulty MB. It shouldn't freeze in BIOS setup. To be absolutely sure you would need another 100FSB CPU or another 440BX board.

I do have another 100mhz cpu, a Pentium 2 that clocks at 133mhz and it still freezes on me in the Soyo combo features menu. Is my motherboard just screwed at this point?

Have you tried installing a different BIOS revision?

giantenemycat wrote on 2026-03-24, 16:27:

bunghole102 wrote on 2026-03-24, 16:18:

AlexZ wrote on 2026-03-24, 16:13:

Sounds like faulty MB. It shouldn't freeze in BIOS setup. To be absolutely sure you would need another 100FSB CPU or another 440BX board.

I do have another 100mhz cpu, a Pentium 2 that clocks at 133mhz and it still freezes on me in the Soyo combo features menu. Is my motherboard just screwed at this point?

Have you tried installing a different BIOS revision?

I'm not exactly sure how to do that, I don't have another chip and I'm not familiar with flashing the BIOS.

Leave the CPU frequency alone and set the "CPU Host/PCI Clock" to 100/33Mhz

NeoG_ wrote on 2026-03-24, 22:07:

Leave the CPU frequency alone and set the "CPU Host/PCI Clock" to 100/33Mhz

Unfortunately the option for that is under the same menu, the "Soyo combo features." As soon as I access that menu I can't select anything and I have to reset the computer.

bunghole102 wrote on 2026-03-24, 22:12:

NeoG_ wrote on 2026-03-24, 22:07:

Leave the CPU frequency alone and set the "CPU Host/PCI Clock" to 100/33Mhz

Unfortunately the option for that is under the same menu, the "Soyo combo features." As soon as I access that menu I can't select anything and I have to reset the computer.

Sorry it sounded like the freeze was when you change one of the options, definitely there is something wrong and I think it needs the BIOS flashed at least. It uses a very common Award 4.51PG bios so you can use AWDFLASH and the BIOS files available on TheRetroWeb.

https://theretroweb.com/drivers/1408
https://theretroweb.com/motherboards/s/soyo-sy-6ba-2

You need to be able to boot into a pure MS-DOS prompt (not in windows) and have the files accessible in MS-DOS, either on your hard drive, a floppy etc.

NeoG_ wrote on 2026-03-24, 22:23:

Sorry it sounded like the freeze was when you change one of the options, definitely there is something wrong and I think it need […]
Show full quote

Sorry it sounded like the freeze was when you change one of the options, definitely there is something wrong and I think it needs the BIOS flashed at least. It uses a very common Award 4.51PG bios so you can use AWDFLASH and the BIOS files available on TheRetroWeb.

https://theretroweb.com/drivers/1408
https://theretroweb.com/motherboards/s/soyo-sy-6ba-2

You need to be able to boot into a pure MS-DOS prompt (not in windows) and have the files accessible in MS-DOS, either on your hard drive, a floppy etc.

It's either this, or you could lean into the limitation and use a 66MHz FSB Klamath instead. A plain old Pentium II 233 would be very fitting for a Windows 95 build.

I just thought the freezing BIOS page could also be a corrupted CMOS - In which case clearing the CMOS and making sure you have a good CMOS battery may help

NeoG_ wrote on 2026-03-24, 22:23:

Sorry it sounded like the freeze was when you change one of the options, definitely there is something wrong and I think it need […]
Show full quote

bunghole102 wrote on 2026-03-24, 22:12:

NeoG_ wrote on 2026-03-24, 22:07:

Leave the CPU frequency alone and set the "CPU Host/PCI Clock" to 100/33Mhz

Unfortunately the option for that is under the same menu, the "Soyo combo features." As soon as I access that menu I can't select anything and I have to reset the computer.

Sorry it sounded like the freeze was when you change one of the options, definitely there is something wrong and I think it needs the BIOS flashed at least. It uses a very common Award 4.51PG bios so you can use AWDFLASH and the BIOS files available on TheRetroWeb.

https://theretroweb.com/drivers/1408
https://theretroweb.com/motherboards/s/soyo-sy-6ba-2

You need to be able to boot into a pure MS-DOS prompt (not in windows) and have the files accessible in MS-DOS, either on your hard drive, a floppy etc.

Definitely gonna try this, I've heard that flashing the BIOS can go badly on occasion but it seems relatively self explanatory so I'll give it a shot and let you know what happens.

giantenemycat wrote on 2026-03-24, 22:31:

NeoG_ wrote on 2026-03-24, 22:23:

Sorry it sounded like the freeze was when you change one of the options, definitely there is something wrong and I think it need […]
Show full quote

Sorry it sounded like the freeze was when you change one of the options, definitely there is something wrong and I think it needs the BIOS flashed at least. It uses a very common Award 4.51PG bios so you can use AWDFLASH and the BIOS files available on TheRetroWeb.

https://theretroweb.com/drivers/1408
https://theretroweb.com/motherboards/s/soyo-sy-6ba-2

You need to be able to boot into a pure MS-DOS prompt (not in windows) and have the files accessible in MS-DOS, either on your hard drive, a floppy etc.

It's either this, or you could lean into the limitation and use a 66MHz FSB Klamath instead. A plain old Pentium II 233 would be very fitting for a Windows 95 build.

I was thinking of doing this too, my neutered Pentium 3 sits at 366mhz which from what you guys are saying seems a little more fitting for windows 95 than 550mhz, and I already have a souped up windows 98 machine for heavier stuff so I may do this but I'm still gonna try and flash the BIOS because I'm not a fan of the freezing.