Refer this page where I looked up your motherboard's details: https://www.wimsbios.com/awardnumbers.jsp
Based on the BIOS ID string, the chipset (as already clear from the pictures) is the SiS 85C471B/E/G.
The motherboard manufacturer is Chaintech.

Once I was able to identify the manufacturer, I looked on Total Hardware 99.
This looks like your motherboard: http://arvutimuuseum.ee/th99/m/C-D/33003.htm

right, I also researched the bios string: the LAYOUT is a 4SLD.3, BUT the BIOS String says it's a 4SLE ! Really weird! I asked the vendor if he once flashed the wrong bios on it (perhaps it still runs even with a wrong bios), but he denied it.

Now I have to find the exact manual for it 😉

Where do you see in the BIOS string it's a 4SLE?
Regardless, it's most likely just a later revision of the same motherboard.

If the layout is the same as in the link that I provided in my previous post (with the jumpers in the same locations), then you can rest assured it's the correct settings for your motherboard.
As such, there is actually no need to obtain the manual for it (chances are slim you will be able to).
My experience has been that Chaintech's support (in terms of drivers, manuals & BIOS updates) for their older motherboards is very poor.

https://www.wimsbios.com/chipset/2C4I9.jsp

if you continue your link, you'll see the rest:
2C4I9C31-00 Chaintech 4SLE

therefore.. 😀 but the 7 pages of jumpersettings etc. are already enough i guess 😀

No problem - I was looking at the BIOS post screen in the pictures that you posted, not realising you were actually referring to the link that provided.
The link that I provided most likely refers to a slightly older revision, but from what I can see, the layout is exactly the same.