Hmm the 54170AJ have a "2 WE write control" and so does the 514270A J....and they same 400mm 40pin. But the pinouts do not match. Pin 15 is A09 on 514170 but NC on the 514270
54170A: https://www.datasheetarchive.com/datasheet?id … erm=HM514170AJ7
54270A: https://retrocdn.net/images/9/9b/HM514270_datasheet.pdf
One of the others here may be able to help more....

Something else I noticed was 512-refresh for the 270 instead of 1k refresh on the 170.
I've been burned in the past mixing up 2k refresh DRAM and getting 4k-refresh DRAM instead, which then didn't work at the full capacity. Different refresh times often mean different row & column layout and that is in the case of the HM514170 vs HM514270. The '170 has 10 address lines, the '270 only has 9, so I can't say whether it would be compatible or not but the memory going into the 2nd bank should really match the 1st bank. Technically I think that lower refresh would be better with old equipment like this but mixing types might cause problems.
This datasheet inciudes both types so you can get a direct comparison with block diagrams. My understanding is that memory is like a spreadsheet made up of rows and columns, 512k refresh has the same number of cells as 1k refresh but a different layout of rows and columns within the chip.

You don't need the part code to be exactly the same - specifically the A letter signifies kind of the version of the chip i.e. HM514170 - A - J - 7:
HM514170 - this part is important, it specifies the vendor, size, refresh cycle, layout of the DRAM. You might see parts ending in 1, 5 or 7 instead of 0, stick with 0 in this case. Different numbers at the end usually mean EDO which won't work with all memory controllers and might not work alongside existing FPM
A - not important, this is the revision code. You can get a part with "B" or "C" here and it should work exactly the same as the "A" part
J - Important, this signifies the package type, J means SOJ. The J means the shape of the leg in this case, which folds under the chip for SMD or socket fitting.
7 - Important, you can go lower but ideally not higher. This is the response time of the memory and 7 = 70ns. 8/80ns might be too slow for your video memory

So you can get the B/C/D versions of the chip. You'll probably need to turn to utsource or aliexpress to get them, can't seem to find any on ebay.

Beyond that though, memory does adhere to JEDEC standards so another vendor's chip should work in place of the HM514170 if all the parameters match up. Seems like 1k refresh 256k x16 memory is actually really rare so I'm not going to give alternative part numbers since they're even less available 🙁 ... Just get HM514170, there seem to be a few on aliexpress including 3pcs for ~$10.

Oh also, please post some pictures of that computer - there doesn't seem to be much to refer to for what memory is required or what the board looks like

ok that explains why i can't work with the 270 anymore
than VGA with 256 colors. Thanks for the clarification!
let's see if worked with aliexpress so far
never ordered anything through them.
tt0ny

tt0ny wrote on 2023-11-27, 17:43:

let's see if worked with aliexpress so far
never ordered anything through them.
tt0ny

I wish you good luck. May the loss be minimal. Holding my thumbs you get something remotely usable.
Its like gambling but with even less chance of winning 😼