Life has been hectic but I had a chance to finally test some cpu upgrades in a Teradrive and I can confirm they work. After doing some of my earlier Teradrive modifications as seen on this thread: https://assemblergames.com/threads/sega-teradrive-simms-ram-upgrade-help-needed.62782/ I got a hold of some cpu upgrade boards. The biggest/huge improvement came with the Rev to 486 board that runs at 66 Mhz. This upgrade board also comes with a socket for an internal Math co-processor. Without it the Teradrive displays as 486SX Once fully populated and as described by the Rev to 486 manual, it brings it to 486DX status. Others tests. Sound Blaster Pro 2 test (don't forget the Teradrive lacks the -12V -5V power lines) Sega Teradrive in composite video mode so it can run the demo in full color. Next in line was the Kingston SXNow (386) upgrade and while it works is on the slower side and there is also one major caveat, while on the socket & due to the aesthetics and board size, some of the cpu upgrade chips make contact with some of the Teradrive board IC's. I was able to still install/test it while the board was inserted at an angle .