Smart Genius famiclone computer problems

[gamebox]

Hello all.

I've been experimenting with my famiclone type computer for quite some time, but ever since I got it it had some issues I'd like to finally sort out. It does function (mostly), accepts cartridges, displays a game and plays sound, but I can't get it to react to a controller or keyboard button press. So far, the 7805 is working correctly, the main CPU which is on a small pcb holding the cartridge connector operates too, all connections between that PCB and the other one with RF/joypad and keyboard connectors/7805 are testing ok. When I attach the joypad and test voltage on its PCB pins I get a small 0.01V drop during the key press. The same RF PCB holds another chip which seems to be some sort of "interface controller" as it connects to the keyboard itself, but at least it shouldn't affect joypad use since I found that joypad pins on a PCB trace directly to the small PCB holding the CPU. The CPU PCB itself has a couple of electrolytes, a crystal, some resistors and 2 small capacitors. Any ideas what to test?

If recall correctly, I once (long ago), got some sort of reaction to a keyboard button press, but not all keys worked and I think it also misinterpretted keyboard presses - wrong letters appeared.

Thanks for your attention and help.