Yes, that's my understanding too, and I appreciate the offer of one, thanks.stephen_usher wrote: ↑Mon Oct 07, 2024 12:03 pm Looks like an address line issue. Check for shorts. Probably one of the higher address lines.
What you get on the screen very much depends upon the mode the VDP is in and what graphics planes are being used as to what memory it will use.
The PAL version of the TI99/4A does use the same chip, as does the Memotech MTX, MSX-1, Spectravideo etc.
I should have one in stock if necessary.
Funnily enough the address lines were next on my list of checks based on this from the service manual:
Basically if the VDP is good it's one or more of the RAM chips, if not then the VDP is bad...
It does then go on to say check the CPU and system ROM (U1 and U2) but since the games are running, I think that they are fine.
However I did just do a continuity test on the address line of the RAM and found pins 6 &10 in the sockets are not connected to each other, however if I flip the board and run the same test, they are. I need to go away and verify that as it seems a bit weird to me and I need to check my work.