Try to install the 486 DX 50 in an underclocked DX 33 configuration first.

This board is the Soyo SY-4SAW2. The difference between the 4SA2 and the 4SAW2 is that the 4SAW2 is the cost-reduced board that only supports a single bank of cache, wheres the 4SA2 has 9 cache sockets for a dual bank cache. The digit at the end is the amount of cache the board is originally equipped with. 2 means "256kB of cache" and 5 means "512kB of cache".

I just found some info about the 4SAW2 board, it really looks just the same! And I also just noticed that JP15 is hardwired (no pins) but there’s a JP14 next to it which is set to 2-3.
But then again, according to stason.org JP14 should be set at 1-2 closed - for ALL cpu speeds except 50 and 150iMHz so I think that should do the trick!

Kouwes wrote on 2022-11-21, 15:09:

I just found some info about the 4SAW2 board, it really looks just the same! And I also just noticed that JP15 is hardwired (no pins) but there’s a JP14 next to it which is set to 2-3.
But then again, according to stason.org JP14 should be set at 1-2 closed - for ALL cpu speeds except 50 and 150iMHz so I think that should do the trick!

That's likely the PCI clock divider, then. 1-2 means to run the PCI clock at FSB clock, and 2-3 means to run the PCI clock at half the FSB clock. This means if you jumper for 40MHz, you get the PCI bus clocked at 40MHz, unless you set JP14 to 2-3, in which case you would get PCI clocked at 20MHz. Not every PCI card is happy with just 20MHz (e.g. the Highpoint IDE controller refuses to work at that PCI clock), and obviously, not every PCI card is happy with 40MHz (although the same Highpoint IDE controller works without problems for me at 40 MHz).

@mkarcher: thanks for helping me find the right mobo model!
According to the manual you actually have to set/check 19 jumpers!!!!!
I‘m not so sure anymore if I really want to touch this running system…😅
The 486dx50 runs internal at 50MHz, does it?

Kouwes wrote on 2022-11-21, 15:55:

The 486dx50 runs internal at 50MHz, does it?

Yeah. It runs at 50MHz internal and 50MHz external. When Stason writes "50i", they mean 50MHz internal only, implying (but not stating) 25 MHz external using a DX2 processor. So 50i on stason.org is just the same as "25". The same is true for "66i" which just means 33, "100i" is not unique, it could mean 50MHz (external) * 2 or 33MHz (external) * 3. In fact, they use it to mean 33MHz (external). The speed of "150i" you quoted is 50MHz (external) * 3, so that's why 150i and 50 share the jumper configuration.

Great info, thanks!!