68kMLA Classic Interface
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| IIfx Memory | |
| Posted by: campbellashe on 2026-03-19 15:14:37 As I'm new to the IIfx, I'm trying to find memory for this computer as I only have a total of 8MB, what is the landscape like? It looks like given the unique 64 pin 70/80ns DIMM requirements, that they are hard to find. No real listings that I can easily find. Has any one made them? I did see a schematic on GitHub.... Or are there people out there with 4MB DIMMs willing to sell? Would love to get to 16 MB or 32 MB if able. Thanks. | |
| Posted by: joevt on 2026-03-19 16:12:40 There's this: https://github.com/hanshuebner/maciifxsimm I haven't tried it. | |
| Posted by: finkmac on 2026-03-19 18:14:42 i made some of those, they work well. | |
| Posted by: campbellashe on 2026-03-19 18:17:43 Thanks @finkmac I've been able to create the Gerber files from the GitHub site above. Priced out the creation of the PCBs on JLCPCB for around $7.00 for 15, and the stencil for around $16.00. The slow shipping is about $18... would need to source the chips -- can get the KM41C16000CK chips from UTSource for about 50 for $50 dollars. I've just never used stencils before... just don't want to get too far down this.... however if memory is un-obtainable then this might be the best route. Glad you were able to create them.... does this pricing seem right for your prior project? Did you use stencils? | |
| Posted by: finkmac on 2026-03-19 18:37:52 just remember to choose the right thickness. as the github project says, it's best to use a reflow oven type soldering process... that does indeed involve the stencil. | |
| Posted by: campbellashe on 2026-03-20 15:48:16 On the V2 of the PCB of the Gerbers (if you plot and generate through KiCad) there are now small capacitors indicated above each chip....anyone know the value of these? | |
| Posted by: campbellashe on 2026-03-20 18:33:41 I think the capacitors are standard decoupling/bypass capacitors with 0.1 uF values? Just checking. I wrote Hans Huebner to ask.   | |
Posted by: finkmac on 2026-03-21 21:54:17I think the capacitors are standard decoupling/bypass capacitors with 0.1 uF values?correct. I can't remember the exact part number I used, but that should be the right value. | |
| Posted by: campbellashe on 2026-04-08 07:47:02 Well the journey to create 16 MB SIMMS was successful.... now at 128 MB in the IIfx. Used the above git and printed at JLCPCB with a stencil (make sure the 1.2 mm size is selected on the board options) -- worked great. Just used a credit card to spread the paste. Used the SAMSUNG KM41C16000CK-6 from UTSource Used the Cap 0.1uF 50V Z5U 0805 for the capacitors (Digikey: 399-C0805C104M5UACTUCT-ND) -- small little buggers.... Lots of trouble shooting with continuity of the pins with the solder paste and looking for bridges. As well as just getting the SIMMs to sit properly in the slots. It was hard to troubleshoot the first 4 as they all had to work. Once a stable 4 then you can swap out the last 4 into the mix to narrow down any problems. Lots of fun...  [td] [/td]   | |
| Posted by: finkmac on 2026-04-08 08:09:06 excellent work! i assume you went with the reflow oven method? what kind of oven did you use? As well as just getting the SIMMs to sit properly in the slots. It was hard to troubleshoot the first 4 as they all had to work. Once a stable 4 then you can swap out the last 4 into the mix to narrow down any problems.this was the biggest annoyance. I ended up having to tin the contacts a bit. | |
| Posted by: campbellashe on 2026-04-08 10:10:38 Actually, I used hot air and worked well. Things I learned: A) I set the hot air to 360 and flow at 30, worked great at about 4-5 cm above chips. B) I first tried to use hot air for all the components, but the capacitors blew off… I therefore moved to soldering them by hand. I have a microscope and a needle nose for my iron to get into the small space between chips C) tested continuity on all pins if error D) tested pairs to see if bridges underneath the chip E) the contacts were an issue, I had to reseat them multiple times - even a little solder bump can cause an issue F) I was worried about the Z5U a bit but they worked fine, make sure to get the 0805 size. G) using Kicad I did use the pcb view to network the traces some. But just checking GND and VCC and looking for shorts found most problems Overall a fun project. The chips were the most expensive part other than shipping and tariff fees. Thanks to Hans Hubner for his great design and git depository. I wrote him and he confirmed the capacitor value. | |
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