I have an old video card for a computer from the 1980s era, but unfortunately the memory chips on it have gone bad. As it's quite a rare device today, I would like to repair it.
Unfortunately I can't find anywhere that sells pin-compatible replacements for the old
44256 ICs. These were apparently quite widely used ICs - the
41xx is 1-bit memory, and the
44xx is 4-bit memory, with the
xx64 having 64k addresses and the
xx256 having 256k addresses. All are 5V TTL logic.
Is there an easy way to replace these failing chips? If there are no compatible replacement chips being manufactured anymore, is it possible to find a chip that's similar enough that it could be substituted with minor modification? What would I be looking for? These are DRAM chips, so I'm not sure if they could be substituted with SRAM chips or newer types of memory ICs, since the DRAM refresh may be too slow for newer chips to maintain the data.
The chips on this card appear to be arranged in two independent banks of four
4464 chips each, but I have other failed cards with different arrangements so it would be nice to aim for the more general case of 1-on-1 chip replacement rather than trying to replace a group of them with a modern larger capacity chip - only since that solution may not work elsewhere.