Fabbing 30 pin SIMMs

[tt]

I was wondering about the feasibility of making new 30-pin SIMMs and wanted to see what thoughts members here might have. Finding 16MB modules can be bit tough if you have space constraints like within the SE/30 chassis. Could making our own be feasible without being too expensive?

trag pointed out the simplicity of the circuit here viewtopic.php?f=7&t=18527 So perhaps it would be feasible to make 30-pin SIMMs by fabbing them at SeedStudio and finding the appropriate chips if they are still being manufactured. I tried finding a source for the IC used in my 3-chip SIMMs (KM44c16100BK-6) but could not readily find any in stock. I would think a 2-chip design would be optimal to reduce complexity/cost and power consumption assuming it is compatible with most machines.

 

[Unknown_K]

http://www.ebay.com/itm/LOT-OF-TEN-16MB-FPM-NON-PARITY-70NS-SIMM-30-PIN-5V-16X8-/330590860017

$10 a stick ($40 a set of 4) in groups of 10 , would be hard to beat that by making your own.

 

[tt]

Good point, but I bought some from them a few months ago through their website and had to send them back since they were the taller type that cannot fit in all the banks of an SE/30 due to clearance issues. At the time they said they had no shorter SIMMs, maybe they have some "new" inventory now, but a lot of times the photos posted are not representative. OWC could not confirm the height of their SIMMs, but someone that ordered from them recently said they received the taller type.

 

[Unknown_K]

I don't know what they stock to be honest, or how "NEW" those parts are. You need SIMMs for compacts, not sure what the other buyers would need them for and if the premium of you making SIMMs would be worth it to them (there seems to be no clearance issues with old PCs or Macs like the 950 for example). I stuffed 256MB into a 950 just for the hell of it, hard to justify the expense when you don't realy need that much RAM. I did have 128MB in a SE/30 but 32MB seems to be good enough and I removed it.

The only time making small batches of RAM is warrented is when it just cannot be found anymore and the market is big enough to make it worth the effort. Very few sets of 16MB IIfx SIMMs seem to have been sold (and the maker quit when a set of 4 would only bring in $60 if they did sell) and those are unobtanium.

I know somebody made some GVP 64 pin SIMMs for Amiga users with GVP hardware, but those people pay crazy prices for that kind of stuff and it is not available anywhere else.

 

[tt]

I'm not really interested in marketability/profitability or whether or not having a certain amount of RAM makes sense for a certain computer, I'm just trying to see how feasible it is given availability of components, etc. :b&w:

 

[uniserver]

4's and 8's pretty easy to come by?

Is the se/30 picky besides just a clearance issue?

 

[Unknown_K]

8's are rare and some macs have issues with them, same with 2's. macs in general since they take non parity and parity 30 pin SIMMs are not that picky about RAM (except the II, IIx models that need composite SIMM).

I don't understand what you mean by marketability/profitability of 16MB SIMMs, if money is no object and you don't care about selling them then ANYTHING is possible to make, they were commidity RAM and the specs are out there. All I was trying to say is you can find them cheaper then it would cost to make them so there isn't a market for them.

 

[zuiko21]

2 & 8 MB SIMMs do not work on the SE/30 -- just 256K, 1, 4 & 16 M

The IIsi (and I presume the IIci too) seems to take almost anything 30 pin, parity or not, composite or not, including 2 and 8 MB sizes.

But the clearance issues aren't unique to the SE/30: the Quadra 700, for instance, has a tighter spacing between sockets, thus some SIMMs with chips on both sides won't fit.

 

[tt]

I don't understand what you mean by marketability/profitability of 16MB SIMMs, if money is no object and you don't care about selling them then ANYTHING is possible to make, they were commidity RAM and the specs are out there. All I was trying to say is you can find them cheaper then it would cost to make them so there isn't a market for them.

I know it doesn't totally make sense, part of this is driven by wanting to make something "new". When I looked for SIMMs that met my specs, the cost was getting in the realm of maybe just looking into making it myself and learning something new along the way. My thinking is if the SIMM takes 3 main components and each component is $3-4 then it is probably feasible cost-wise. I'm just not sure what parts would be best to use, if they are still manufactured, or more contemporary/available equivalents could be used.

 

[trag]

The memory chips are available, if you are willing to do some extra work.

Get 128 MB 72 pin SIMMs or 64 MB 72 pin SIMMs. Desolder the eight (or 16) 16M X 4 memory chips. Put two each on your home designed 30 pin SIMMs.

One $16 128MB 72 pin SIMM will supply enough memory chips for an entire SE/30, provided you don't destroy any in the desoldering/soldering process.

http://www.ebay.com/itm/KMM53632000BK-6-128MB-32x36-60NS-FPM-SIMM-/110677960034?pt=US_Memory_RAM_&hash=item19c4eba562

A two-layer SIMM should work fine. I used a two-layer design for my IIfx memory, and Doug is using a two-layer design for his ROMs.

As others wrote, it may not be worth the time/money, but it would certainly be fun. I've often considered running off a batch myself.

 

[uniserver]

well how much does it cost to have a company fab up some blank simms and send them back to you?

i would assume were talking about made in china…

just like how much does it cost for the 8mb rom simms.

 

[trag]

well how much does it cost to have a company fab up some blank simms and send them back to you?i would assume were talking about made in china…

http://www.seeedstudio.com/depot/fusion-pcb-service-p-835.html?cPath=185

For the Seed Studio 2-layer boards, it's $2.50 a board. I think that's their price for up to 5cm. X 10 cm. (2" X 4"). It's $10 + $15. It puzzled me at first, because I kept reading it as being $15 for 5 cm X 10 cm.

So, a set of eight of them (128 MB of RAM) would cost $25 (PCBs) + $16 (chips) + ~$6 shipping + supplies (solder and the like). With two circuit boards left over.

 

[tt]

Thanks trag, that's a clever idea.... I was hoping you would chime-in since you have a bit of experience in this area.

The 3-chip SIMMs I have have 2 DRAM chips and the other I thought was maybe parity, or is it some kind of controller? Without looking at P/Ns It looks like the 128MB 72pin SIMM also has them.

 

[trag]

Yes, the extra chip is a X 1 chip for parity. If you scavenge from a 128MB SIMM you get a bunch of 16M X 1 chips as a by-product. That's why I built both two-chip and eight-chip IIfx SIMMs. The X4s are a lot easier to come by, but they require me adding a couple of ICs to the SIMM to handle the IIfx's special write buffering scheme. That's not an issue on any other Mac, so one can just use the X 4 chips by themselves.

 

[Trash80toHP_Mini]

tt, in another thread; you or another member were wishing for a way to kick-start development for boards that require 4 layers in order to make all the connections.

Suggestion:

Almost every single sided PCB that I've seen in PSU and KBD matrix applications, wires on the component side jump across across traces on the copper side, effectively implementing a two sided layout on a single sided board.

Doing a two sided "Seed board," with vias designed in for patch wiring these same impossible connections would effectively convert a two sided proto-board to four sided function, sans the additional ground fill planes, of course.

 

[tt]

I was thinking the PDS connector necessitated at least 3 layers since there are 3 rows of pins close together, but the Asante card sneaks two lines between each pin, so if that clearance, tolerance and minimum feature size scheme is allowed by the fab-house, then I could see it done with a 2-layer board. There may be electrical reasons for needing more than two layers though, but that determination is out of my design space.

I don't see any reason why a 30-pin SIMM cannot be done with two layers without digging into details, but I think dougg3's ROM design shows it can be done.

 

[James1095]

That sounds like a fun project, I'm not sure why it never occurred to me to try it. I've used Seeed Studio many times for PCBs and have been very impressed. The quality is quite good, delivery can take close to a month but the price is a fraction that of the next lowest cost fab house I've found. The base price is $9.90, with larger sized boards adding on top of the base price. The dimensions they list are the maximum dimensions, smaller boards are fine. I recently had a batch of 10cmx10cm PCBs made and for 10 boards it worked out to only $2.50 per board. Shipping is free if you spend $50 so I get 2-3 designs ready to go and order them all at once.

Somebody mentioned making some IIfx RAM SIMMs, do you have the PCB layout available for those? It's something I'd be interested in doing if I ever get my (badly corroded) IIfx resurrected.

 

[Trash80toHP_Mini]

I'll throw a knuckleball into the works at this point, this one has been on back burner for quite some time, but I just remembered a recently downloaded pic of a similar adapter.

Instead of moving just the 72 pin DRAM ICs back a form factor generation. Move the entire 72 pin SIMM back a generation by converting a 72 pin socket (or more?) to the older 30 pin SIMM form factor.



I've always wanted to do a "reversed-funnel" SIMMspender™ hack of ye 'ole SIMMsaver Hack. Three bare minimum profile RAS-CAS line address transfer SIMMs would be wired up to one larger SIMM that lays a 72 PIN SIMM flip-flopped right back across the top of them.

View attachment 16952

Maybe it's more of a Knucklehead throwing a Screwball into the works here. All the signals would need to be reversed to match the banks of the "backwards" 72 pin SIMM socket.

Installation of the adapter SIMM and the 72 pin SIMM will probably need to be done simultaneously to keep the adaptation low profile. hold the two ready to click into their slots then and push them down together like two legs of a parallelogram for near simultaneous clicks.

Removal should be fun too! }

The original concept involved a single adapter PCB and patch wiring the additional connections. This way no MoBo modding would be required. It'd be a lot more straightforward for most to do.

These are the less attractive configs available in terms of height.



The top version should be easier to install, but the overhang may not fit in the SE/30.

The middle version uses a more difficult to source flat SIMM Slot Connector and the screwball wiring setup. Probably low enough for most Macs.

The bottom version uses it as well, but could be silly looking and use the angled connectors for a straight thru, but very high config.

The lower two, with jumper settings to re-arrange the RAS/CAS line feed, might be staggered to convert adjacent banks.

Three of the four might work in tandem banks.

My first choice, the most difficult to install of course, along with the top, of the alternate choices, might work in a 4x4 bank config if right and left handed versions were to be made available.

. . . or it's a silly idea all together due to SIMM type incompatibility. :-/

 

[Gorgonops]

recently downloaded pic of a similar adapter

Just for edification, the dinguses hanging off that PCI slot adapter are there to take a couple of the unique select/arbitration lines from two of the motherboard's PCI slots and connect them to the appropriate pins on two of the adapter's slots. PCI isn't a *completely* parallel bus like ISA/S-100/whatever; each slot has a few dedicated lines running from it to the PCI controller to handle selection and arbitration. (In other words, a PCI controller has to know *which* slot a card is in, unlike something like ISA where in theory you could extend the bus infinitely via a passive slot extender, subject to electrical loading and propagation time limitations, and the system will have no clue where on the bus a card is located.) If one or both of them aren't plugged in the associated slots on the riser won't work.

(In theory you *can* add more slots to a PCI slot by using an "active" riser that itself has a PCI-PCI bridge on it. But from a software standpoint that's not completely transparent.)

A 72 pin to 30 pin adapter would need at least 8 connections running from each of the "satellite" SIMM slots to the "main" slot the 72 pin socket's plugged into. Any cables would have to be kept *very* short and shielded, so the thing would be utterly monstrous to plug in. There may also be issues with faster machines experiencing errors because of the almost unavoidable timing "skew" you're going to end up with because of the different total wire lengths for each of the four 8 bit banks. It might work, but it would be an even grosser hack than SIMMsavers were in the first place.

(I never got the point of SIMMsavers. Every time I remember upgrading motherboards to one using a newer memory form factor the price of memory had dropped enough it made more financial sense to just buy more new memory than I had in the first place than try to save the old stuff. I can see some edge cases where if you'd *really* broken the bank maxing the memory on the last machine they might save you a few bucks, temporarily, but... factor in the headaches and it's still a stupid idea.)