512KB VRAM SIMMs

[trag]

It seems to be getting harder to find the 512KB SIMMs.   Someone want to run some off using these:

http://www.ebay.com/itm/271605768758?_trksid=p2060778.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

TC524258?

These are the chips the original VRAM are built with, but in a SIP package instead of SOJ.  I'm not sure one could get the SIPs to sit flat enough, but that's a good price on the memory.

Alternatively, I think one could use these (KM4216C256) to build a VRAM SIMM.  These are the chips that were used on the PCI PowerMacs 1MB VRAM SIMMs, but they seem to have the same functionality, just 4 times wider, as the original chips on the 512KB VRAM:

http://www.ebay.com/itm/131219842210?_trksid=p2060778.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

 

[Trash80toHP_Mini]

I'm in for some of the Z-SIPs, those are what's needed to upgrade quite a variety of VidCards.

Couldn't you make a T-Shaped PCB to give you an installation lever and mount those on either side to edgecard teeth to keep the profile fairly low?

 

[wilykat]

On many Macs I've seen that supported 512k VRAM SIMM, it's almost always a single VRAM slot and next to a RAM slot. It seems if you design the board with through hole and mount the ZIP style RAM chips on the "back" side of the board instead of the typical front, it'd avoid clearance issue with existing RAM SIMMs?

Alternately make the VRAM SIMM board taller so the chips would be more than an inch higher than usual to clear most of the typical RAM SIMMs. It might be a problem in LC style box and other low profile housing.  I haven't looked inside an all-in-one LC like 550 for many years, I can't remember what the clearance are like there.

Or are there Macintosh that can use 2x 512k?  Could there be a 90-degree angled connector that would allow the ZIP style package to lie flat on the PCB and still keep the overall thickness from interferring with other components?

 

[Trash80toHP_Mini]

The 256k VRAM SIMM from my 475 is .75" tall and there's another .15" to bring it up to the level of the top of the PSU. Is there any tighter fit than in an LC case? If not, we've got .9" of PCB to work with for this. If we can't scrunch it down low enough to fit into the LC Case, what might be the next threshold for Max Headroom? ;D

I pulled the TrueVision NuVista*** out of the Magic Plastic Shoe Box of NuBus Goodness™ in order to give the ZIP28-P-400 Package a good look. These are TC524256AZ-10, But they're from Toshiba, so they're close enough for govt. work.

@trag: is there any particular reason why the ICs are flip-flopped on the 256k SIMM?

How many layers make up the VRAM SIMM PCB?

*** Thought I'd share this VideoCap/Editing Card Roundup article.

.

 

[trag]

@trag: is there any particular reason why the ICs are flip-flopped on the 256k SIMM?

How many layers make up the VRAM SIMM PCB?

I haven't looked at one in a while, but usually, the orientation of the chips is chosen to get the pins into convenient locations for board routing. So it might make corresponding address pins line up with each other nicely, or get all the data pins in the right place or something like that.