Looks a lot like this one: https://arvutimuuseum.ee/th99/m/E-H/32077.htm

Seeing as the CPU voltage jumper is soldered to 5V, I wonder if this is a budget version of that board. I thought it was odd seeing a DX-33 given it seems to be a DX4-era board but I guess that explains why.

Thanks. It in fact looks similar.
DX-33 is there simply because I do not have anything better in my collection at this point.
Board had some damage from battery acid spill, resulting in "keyboard error". Fortunately cleaning affected part of the board and resoldering socked resolved that problem.
There are still some other issues. For some reason board doesn't boot byt itself after being powered on - it needs to be manually restarted by shorting RST pins. There are also stability issues. Some games (Doom and Raptor for example) crush the system. I am not sure if it is fault of a memory, cache, some I/O conflict or wrong jumper settings.

I also will be grateful for one additional information: does DX-33 od DX-40 require heatsink/cooler or can it safely run without it?

Atlantis wrote on 2020-07-22, 17:59:

I also will be grateful for one additional information: does DX-33 od DX-40 require heatsink/cooler or can it safely run without it?

Heh, I opened that can of worms recently although it was about DX2s. (486DX2 heat sink debate)

If you read p. 209 of the datasheet for the DX-25/33/50 (https://archive.org/details/bitsavers_intelda … e/n209/mode/2up) as long as there is some case fan airflow the allowed ambient temperatures with no heat sink are pretty generous, unlike a DX2.

I haven't worked inside a DX-33 system in ages but I can't remember ever seeing one with a heatsink. Only DX2 and later. Someone in that thread does how an OEM DX-33 heatsink however.

If you're concerned, perhaps put a front fan in your case (or turn on the air conditioning...)