There is one of these on eBay right now, http://www.ebay.com/itm/152280830199
It looks like a cross between a Chaintech 486SPM and an MSI MS-4144, both of which are awesome boards.

The 486SOM has solder pads for a PS/2 mouse header, so getting a PS/2 mouse fairly straight-forward. Both the 486SPM and MS-4144 were pretty easy to get a PS/2 mouse working, e.g. Adding PS/2 mouse components to a Chaintech 486SPM

Unfortunately, I have not had the honour to test out a 486SOM, but I would guess the performance and overall functionality is similar, if not the same, to the 486SPM and MS-4144. You may even be able to use the BIOS from those boards. At $60, I think this is a real steal of a deal.

Hope it's okay to revive this ancient thread, as I just yesterday opened the dx5/133, that was retired from work (after 15'ish years in storage). It sports the 486SoM board with an AMD dx5/133.

As for what I can see from the pictures, it has all 8+tag cache sockets populated with 32x8k making it 256 kiB of cache, right?

I can't find any documentation on the board, but as you state, feipoa, it looks close to the 486SPM - except for the CR2032 and other jumper placement. But the SPM seems to be capable of up to 1MiB of cache - isn't that totally overkill for a 486 system? Would the 486SOM also be compatible with 1MiB? Apparently, being a socket3 and taking from the silk screen on the PCB, I would suspect that it will run a POD 83? Am I right?

Also, with up to 50MHz clock, it should be capable of some fun?

computergeek92 wrote on 2016-10-15, 12:23:

I saw a 486SOM board online. It's one of the late model PCI ones. I'm guessing it's made by Chaintech, cause the 486SPM looks similar. Any knowledge on this board? Are they easy to set up with an AMD 133MHz 486?

http://www.recycledgoods.com/sis-486som-socke … stem-board.html

Yes, definitely Chaintech. I have similar 486SPI P103A board and it's Chaintech.

Yes, its Chaintech. I have exactly the same board, and this Chaintech 4som2. Settings on photo for AMD AM5x86-133.

Manual for this board:
http://www.elhvb.com/mobokive/Archive/Chainte … /4som/4som2.gif

It looks like 4SOM 486SOM and 4SOM2 were used for one and the same board.
http://www.motherboards.org/forums/viewtopic.php?t=33045

Maybe some modification.
BIOS update from web.archive.org.
http://web.archive.org/web/19991117232109fw_/ … DEL486.htm#4SOM

I just acquired this exact motherboard and now have the PS/2 port working. All the required components already exist on it, only the header needs installation, and the pads in the lower left corner of the PCB marked JP4 (see image) must be shorted. JP4 connects IRQ12 to the keyboard controller, without this the system will hang or behave spuriously due to PS/2 data being interpreted as keyboard data.

No bios modification was necessary however I did have to use the PS2SUPPC.COM TSR driver program (from Native PS/2 mouse implementation for 386/486 boards using the keyboard controller) to enable the PS/2 support during boot as the bios provides no option to enable this from factory.