Yay! It worked! As usual I made a mistake first, and soldered the first chip wrong way. Desoldering was slow and painful, but eventually I did it. After this I resoldered both chips correctly and tested the cart in my MSX TurboR GT. It worked! All but four Konami megarom games can be played with upgraded SCC+. Exceptions are: Metal Gear 2, Nemesis 3: Gofer, Knightmare 3: Shalom and Space Manbow. It is ok, I can still play those on Padial’s flash cartridge. It is just too much trouble flashing it - each time I have to switch four jumpers…
Big thanks to BiFi for writing SCC+ Rom Loader.
I did a fairly decent job at opening the case. Unfortunately I damaged two tiny plastic hooks on sides of the cartridge case. At least I didn’t make too many visible scratches. I guess I’ll have to use a bit of superglue to put everything back together.