Hi everyone.

I'm Bobby and this is my first post. In fact, I recently decided to enter the world of MSX by purchasing a National CF-2000, therefore Japanese MSX1 type NTSC standard. After about 1 hour of use, glitches appear on the screen. One hypothesis is that it is the vdp and in fact I'm looking for a reliable TMS9918A (I'm told that the "Chinese" ones found on eBay are not). In particular, in the basic environment, after about 1 hour of use, the characters skip and become Japanese katakana. Could it also (or only) be a matter of replacing the RAM? I already replaced the VRAM but nothing has changed.

I thank anyone who has an idea and wants to help me.