I've been making these particular boards in one form or another for about 25 years, and they use a 1Mx8 EPROM that contains 128 lookup tables each 8K long. It's time to get into the 21st century. Trouble is, using flash is a whole lot more complicated than EPROMs. Looking at the data sheet I have no idea where to start. What would be really simple is a daughter board that could plug into the existing 32 pin DIP socket. Some level translation needed because the main board is 5V. And maybe converting parallel to serial and vice versa, depending on the actual chip. And some means to program it before it gets plugged into the main board.
Can anyone give me some pointers. I have no idea where to even start.
I'm not sure about "
converting parallel to serial and vice versa" that's never going to be practical, but you might find packages other than DIP32 are easier to apply to a daughter board.
That said, you can still buy DIP32 EPROMs eg 27H010 from Digikey, or AT27C0x0 from Mouser etc.
You can use FLASH parts, if you pgm externally and simply tie WE# high.
Parts like SST39SF010A-70-4C-PHE look to be active and stocked and 1/2/4Mb can all fit into DIP32, so that gives you many choices, without needing a daughter card.
For a while Winbond made MTP versions of their W27C010/W27C020 etc, sometimes called W27E010/W27E020, and those seem to show up on Aliexpress.
https://www.aliexpress.com/item/1005003166003152.html