I know this might be a weird question, but does anyone have a schematic of 30 pin SIMMs?
Just like the Mac IIfx, the IBM PS/2 model 30 requires some weird mods to make it work. Proprietary.
Thing is, with SOJ style RAM, its almost impossible cut and redo traces to match it.
So I was wondering if someone had a schematic, and maybe a PCB layout with the correct PCB thickness for SIMM. I know there were threads discussing this in the IIfx stuff, but those RAMs are already pre-modded. Well I need stock modded a different way.
I don't have a schematic handy, but the pinouts are relatively simple to turn into a schematic for a reasonably seasoned electronic engineer (the SIMM pins map directly to IC pins, except for any weird ID lines). What do you need to know?
Also, the thickness isn't a property in layout files, it's something you specify with the manufacturer when you build the PCBs. Standard PCB thickness is 1/16 of an inch (0.0625", 62.5 mils, ~1.6mm). I know 64-pin SIMMs (as used in the ROM SIMMs and the IIfx) are 1.2mm, which means 72-pin SIMMs (very similar) probably are as well; I'd have to compare thicknesses to check 30-pin SIMMs. I have a sneaking suspicion that they may be 62.5 mils as well.
I basically need to make SIMMs for my PS/2 Model 30. Which uses "specially wired" RAM. Problem is, existing SIMMs with SOJ RAM back to back is hard to cut traces. So i figured it would be easier to spin new PCBs, and just remount the SOJ chips. But Not sure.
But, I dont have an existing layout file for the 30 pin SIMMs, as I dont have a set of calipers handy to figure out how to layout the SIMM contacts.
Can you please post your all hardware details here? What are their specifications?
Also where are your schematics and the details of the PCB?
What type of RAM you are using, its specifications?
How did you troubleshoot this till now?
While I do not own a set of calipers, I suspect you are right about the 30-pin SIMMs having the thicker PCB size, just based on casual inspection. I hope someone checks and then posts the answer here. It will nag at me at a low priority for weeks, otherwise.