I started testing this ECS UV486 motherboard and DX4-100 overdrive processor I got recently.
ECS UM486V Socket 3.jpg
UV486 Motherboard Testing.jpg
The board worked fine with a DX-33 and DX2-66 processors. However, when trying the DX4-100, during bootup into DOS it would halt with a "parity error".
Parity Error Bootup.jpg
On a whim I decided to try a newer BIOS chip from another ECS board that uses the same chipset. That worked, and the system was able to boot just fine.
Landmark Test new BIOS.jpg
However, it doesn't detect the L2 cache. Doing some research apparently this is an issue with this chipset that can be solved with a different BIOS. So I've order some EEPROM chips and will hopefully be able to try flashing a new BIOS once I receive those.