I thought I'd start a new topic on this, rather than cluttering up one of the existing ones.
I had my PCBs turn up today for the 4MB SIMM project by "UpLateGeek" https://github.com/UpLateGeek/Let-s-Make-Some-Memories
There is a list of recommended chips to use on the Github, but not having any of these in stock, I disassembled a 72 pin SIMM with LG GM71c17400C chips on it for the main RAM and GM71c4100C chips for parity. I had a good read through the data sheet before doing this and I couldn't see why they wouldn't work. 5V, FPM and 2k refresh.
However, they don't!
They are obviously close, my 386SX will sometimes boot with any 2 of the 4 I made installed, but I get all sorts of weird parity errors, either during post, or while testing high memory. Other times it'll just sit there and beep at me angrily through the PC speaker.
With all 4 installed in my 486, I just get the beeping, no POST.
The other very odd thing is when only two are installed in my 386SX, it will show 2mb of RAM, then boot DOS, which is obviously wrong, as they are 4MB a stick. If I install all 4, it will show up as 16MB.
I'm now a bit stumped as to whether this is something wrong with the modules I have made, or whether there is some weird incompatibility with the two systems I am testing them on. They are both Elonex PCs, a 325X and a PC433.
Can anyone else spot anything on the data sheet that suggests that I can't use the LG chips?
I'd really love to be able to take these PCs beyond 4 and 8 megs of memory.
Data sheet for the 71C17400
https://pdf1.alldatasheet.com/datasheet-pdf/v … M71C17400C.html
Data sheet for the 71C4100
http://www.bitsavers.org/components/goldStar/ … _MOS_Memory.pdf (Page 102)
Cheers
Andrew