I'm the one who bought it. I remember I opened it and inserted some normal cartridges. They DO fit. The first slot has a PCB (ROM cartridge without case) with a very ugly menu to select the slot you want to launch; I think it was in SCREEN 1, just a text. The machine is a MSX1 but I can't remember how much RAM. I took some pictures back then. I don't know if I'll find them. I'll give it a try.
Then maybe you can make some detailed photos of the motherboard, so there is a chance we can find out which motherboard it is?
I had really never heard of this 'hidden MSX' before.
