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68-pin VRAM SIMM “shortage”?


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On 3/12/2021 at 7:52 PM, Flux said:

I recently acquired a Performa 475, but have been at a loss to find 512K VRAM SIMMs for 16-bit colour at 640x480. Photoshop with 256 colours just isn’t the same.

 

I would definitely be interested in a couple of VRAM SIMMs if they can be made.


I recently purchased a brand new, sealed, unopened, Apple 512kb VRAM kit on eBay. I popped it open and was disappointed to find two 256kb VRAM SIMMs inside. I had been expecting a single 512kb SIMM. Needless to say the $40 I paid for it was about $20 too much in the end. Whatever you do, don’t buy any new sealed kits unless you know what is inside for sure. 

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On 3/13/2021 at 7:33 AM, MrFahrenheit said:


I recently purchased a brand new, sealed, unopened, Apple 512kb VRAM kit on eBay. I popped it open and was disappointed to find two 256kb VRAM SIMMs inside. I had been expecting a single 512kb SIMM. Needless to say the $40 I paid for it was about $20 too much in the end. Whatever you do, don’t buy any new sealed kits unless you know what is inside for sure. 


Thanks for the warning. I’ve seen similar issues with ram before, where a 32MB SIMM turns out to be a 2x16MB kit on closer inspection. You were unlucky that you couldn’t see the memory sticks themselves on eBay. 


If individual 512KB VRAM SIMMs go for $40, then I’d say there was at least a small market for making new ones from memory ICs.

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20 hours ago, Flux said:


Thanks for the warning. I’ve seen similar issues with ram before, where a 32MB SIMM turns out to be a 2x16MB kit on closer inspection. You were unlucky that you couldn’t see the memory sticks themselves on eBay. 


If individual 512KB VRAM SIMMs go for $40, then I’d say there was at least a small market for making new ones from memory ICs.


At least it wasn’t a very expensive lesson. Just annoying really. 
 

I value brand new original Apple VRAM at $40/512kb. I’ve been sourcing 256kb lately and they’re presently readily available for under $15 US each in quantity. Given that 512kb are nowhere to be found, are far more useful, and are double the capacity, one could argue the lower limit price should be $30 USD without argument / question. Possibly higher if the market can bear and supply/demand favors it. $40 could be the upper limit and you may have fewer customers at that level. 
 

I could be wrong but that is my estimation of the current situation. 

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The PCBs finally arrived, now if only the capacitors I had ordered before the PCBs had ever shipped...

IMG_0863.thumb.jpeg.cfd584acf0f89e3205f64e02cfd45e10.jpeg

 

Oh well, I suppose they might be fine without the capacitors.

 

So, what tests should I run on these besides just sticking them in and seeing if it goes?

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I'd inspect for short circuits in the marked places after assembling them:

 

1142832_VRAMSIMMTC524258BJv1.0_PCB_PNG.png.9b150e2faa56d11fe2900cf30fa2c35f.thumb.png.6daae995199e00a583e3eafa87c64055.png

 

Putting vias between or very close to solder pads always is a bad idea.

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Anyone know the difference between the TC258257 and the TC258267.   I can probably dig it out of the datasheets, but if someone already knows...

 

I don't really need to know.  Pretty much just idle curiosity.

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On 3/10/2021 at 2:02 AM, Fizzbinn said:

I hadn’t thought about the IIci like this. The old IIsi trick I know and definitely works is having enough “fast” 70/60ns? RAM in bank B where you can set the memory control panel disk cache to 1024KB to consume all of the slower bank A memory. This forces the “vampire” video memory to use the faster memory in bank B. (At least I think that’s what’s happening) My past tests show about a 10% CPU speed improvement:


So I think I got this wrong. According to the IIci Apple hardware developer note in the IIci (and apparently si) architecture RAM banks A and B are somewhat independent, with only bank A being used by onboard video. This means if you can force the OS and applications into bank B bank A will be left for use by the onboard video, meaning the OS/Apps aren’t competing for bank A access providing an overall speed boost.

 

Since the onboard video’s various resolutions/video color bit depths use a variable amount of bank A memory, under 1024KB, setting the Memory Control Panel disk cache to 1024KB guarantees the OS and applications will use bank B. The disk cache would still be in competition with the video memory so the “RAM muncher” apps that do nothing but eat up the bank A memory likely provide a bit more of a boost.

 

I guess the rule for the IIci might be if you are using onboard video there is a real benefit to having 4 x 256KB SIMMs in bank A. If you use a NuBus video card only (nothing plugged into the motherboard video connector) then this likely becomes moot.

 

I think I’m going to start a new thread to explore benchmark this... (sometime soon hopefully)

 

 

 

 

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On 3/23/2021 at 2:09 AM, trag said:

Anyone know the difference between the TC258257 and the TC258267.   I can probably dig it out of the datasheets, but if someone already knows...

 

 

Apparently, nnn267 supports extended data out.   It holds the data on the data pins until, something I don't remember.  I think until RAS goes low again, maybe.  Probably doesn't make much difference in practice.

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Posted (edited)

@SuperSVGA any luck with your new PCBs? I've ordered some of the Toshiba TC528267J ICs and if your schematic has already been demonstrated as working that would give me some confidence before pulling the trigger on a PCB order. I'd be happy to refine your layout a bit and have a reasonable quantity of PCBs made if others wanted one or two boards.

Edited by ttb
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20 hours ago, ttb said:

@SuperSVGA any luck with your new PCBs? I've ordered some of the Toshiba TC528267J ICs and if your schematic has already been demonstrated as working that would give me some confidence before pulling the trigger on a PCB order. I'd be happy to refine your layout a bit and have a reasonable quantity of PCBs made if others wanted one or two boards.

I've assembled a few but haven't been able to test, because unfortunately neither of my LC power supplies seem to  work (even after recapping them) in either of my two LCs. I think the only other computers I have that take VRAM SIMMs are a Centris 610 and a Duo Dock, so I'll have to get one of those out if I can't get a power supply to work.

 

One thing I noticed is it seems like there's a slight dimensional accuracy issue in the SOJ40 footprint, or it's just a mistake from the cheap PCB manufacturer I used. As you can see in this picture, it just barely doesn't line up right:

131844558_ScreenShot2021-04-06at6_58_33PM.thumb.png.4d4c719a8ba03c1c64116b2795b6f761.png

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Dear all!

It looks like the lockdown has inspired us to undertake similar projects!

I am the designer of the purple VRAM modules posted above.

I have made a small quantity of fully tested and working, 256k and 512k SIMMs.

Modules are professionally made with top quality gold plated 4 layer 1.2mm PCB.

My prices are:

$29 for a 100ns 512k module

$19 for a 80ns 256k module

Price include shipping worldwide.

I can be reached directly, or they can also be found on eBay for a little bit more.

 

In the near future I will also have 1MB modules for Power Macs, and I am working on a 68pin module to accept newer 70ns and 60ns VRAM chips

 

 

 

IMG_0443.jpg

Edited by siliconinsider
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On 4/12/2021 at 3:33 AM, siliconinsider said:

I am the designer of the purple VRAM modules posted above.

 

Welcome to the forums!  It's nice to see you here.  I saw these on twitter, I think, originally; they're really nice-looking boards.

 

I'd suggest posting about this in the trading post, you'll get more people noticing it there.

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Hopefully this is on topic (mods feel free to delete if not, I wasn’t sure this warranted its own thread since there’s a related discussion in here so I figured I’d post here first) :

Does anyone know whether 256KB VRAM SIMMs marked as 670-0269 will work with the Quadra 700? The listing I’m looking at only mentions LC models, and the seller hasn’t gotten back to me about compatibility.

 

Additionally, do all 6 SIMMs need to be identical/from the same batch, or will things work fine if one pair is from a different batch and potentially a different speed? My Quadra currently has 2/6 slots filled, it would be nice to only have to purchase 4 SIMMs instead of 6 to max it out.

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I did some testing. Probably not relevant to the topic but anyway, maybe better spend money on better videocard than upgrading vrams...

 

• Macintosh Q700 PPC - Quadra 700 with PPC card and Radius Thunder GT video card 256 colors = 81.2
• Mac Q700 Built in - Quadra 700 with PPC card, video built in, 256 colors = 49.2

• Mac Q700 32 bit - Quadra 700 with PPC card, video built in, Millions of colors = 16.8

 

F5582C4B-A96D-4025-861E-763DD82D9804.thumb.jpeg.101779b91508930d6a3301f15acaa04d.jpeg

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