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| Early Macintosh home brew 4MB memory upgrade board development | |
| Posted by: pezter22 on 2025-04-18 07:01:28 My PCB's arrived this morning - quicker than I thought. | |
Posted by: Builder68 on 2025-04-18 13:28:24Are there any photos of version 3 completed? I am looking to compare parts. The Github page has a dead link for photos. Oops! I forgot to add those connectors to the BOM. Here's a picture of the back. They are 2 mm pitch through-hole JST connectors, like these on Amazon (the link you provided doesn't seem to be working). I actually bought the ones I used from Ali Express These pictures are from the initial PCB run used for testing. The KiCad files on GitHub represent a slightly newer version with a couple of minor fixes and some improvements. The dip switches were the areas that were changed.   | |
Posted by: Builder68 on 2025-04-18 13:48:01  | |
Posted by: pezter22 on 2025-04-19 06:09:14Oops! I forgot to add those connectors to the BOM. Here's a picture of the back. They are 2 mm pitch through-hole JST connectors, like these on Amazon (the link you provided doesn't seem to be working).Very cool. Thanks for the info. I purchased the correct headers for J11 and J12. I must have bought the last ones. Same Amazon vendor had listing on eBay as well. Both are out of stock. 
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I ordered enough components from Mouser to make two. The RAM chips (AS4C1M16E5) are coming from China and won't be here until May. I am hoping while I wait for a diagram to connect the jumper wires from PCB to the board. Currently I have BOMW ROM-inator installed on my 512k. So some direction with connecting it to the board would be greatly appreciated. Thanks again. This is a great project. | |
| Posted by: Joopmac on 2025-04-25 10:59:51 Is it correct i have a empty space at C1? | |
Posted by: Builder68 on 2025-04-25 11:20:41Is it correct i have a empty space at C1?Oops! It looks like C1, a 10uF tantalum capacitor (case code 2312/6032), was mistakenly excluded from the bill of materials in its footprint attributes. So sorry about that! | |
| Posted by: Joopmac on 2025-04-26 05:11:47 Thanks=) i am going to use: 10uf tantalum polymer I do not use yellow tantalum anymore since i saw a capacitor burn like a match on a SE/30 board Addendum for the mouser cart: correct JST headers *The header in my first cart was wrong; SMD and not through hole (the wrong ones are not in stock so probably one does not have these yet) correct JST connectors the pins Mouser is ordered, JLC is on their way and the RAM ic's are here already | |
| Posted by: pezter22 on 2025-04-27 05:49:37 All my parts are in. I am preparing to build two expansion cards. I did create a photo parts location with pin locations. (please correct me if this is wrong). I have all the proper headers, but am wondering about stacking and proper header height so the board can clear the case. Are headers soldered onto the IC and then card is placed on top? Or can the IC's be removed and placed on the expansion card? I haven't seen any images from the top of the expansion board (Version 3) mated to the motherboard. This is a great project. | |
Posted by: Builder68 on 2025-04-27 12:47:44I have all the proper headers, but am wondering about stacking and proper header height so the board can clear the case. Are headers soldered onto the IC and then card is placed on top? Or can the IC's be removed and placed on the expansion card?The GitHub repository's readme explains that you have two options: either solder sockets onto the ICs (piggyback) and male-to-male pin headers onto the expansion card, or do the reverse by soldering the sockets onto the back side of the expansion card and the male-to-male headers onto the ICs. I choose solder the sockets on top of the ICs (piggyback). Oh, one more thing! For the connections at RP2 and RP3, remember to solder socket pin headers to the back of the expansion card. Then, add just one row of male-to-male pin headers to these. On the LB side, solder socket pin headers at RP2 and RP3. This way, all connections will be equally leveled. | |
Posted by: Builder68 on 2025-04-27 12:50:59I haven't seen any images from the top of the expansion board (Version 3) mated to the motherboard.Unfortunately, I haven't had the chance to take pictures with the expansion card installed yet. Right now, I have a mess of wires connected to my LB trying to make another project work. But don't worry, I'll assist you anytime you need. | |
Posted by: Builder68 on 2025-04-27 12:54:13All my parts are in. I am preparing to build two expansion cards. I did create a photo parts location with pin locations. (please correct me if this is wrong).Thanks for the photo! Just glancing at it, I think some of the pin locations might be incorrect. Let me create an image with the right pinouts for us to double-check. | |
| Posted by: Builder68 on 2025-04-27 13:50:39 Alright, Readme.md is updated! You'll now find a picture right after the description of the signals that connect to the JST connectors on a Macintosh 512K LB (630-0118). This should definitely make things a bit easier. I tapped the /RAS signal from the TSM chip (pin n°14), as shown in the recently added picture. However, the table in the readme.md indicates tapping it from the left leg of R4. Don't worry, both locations are the same signal. Use whichever you prefer.  | |
Posted by: Builder68 on 2025-04-27 14:14:27Or can the IC's be removed and placed on the expansion card?While physically possible, I haven't explored desoldering and transferring the ICs. Our design offers a much simpler and reversible solution: remove the card, and your LB is back to its original configuration thanks to the socketed RP2 and RP3. | |
Posted by: pezter22 on 2025-04-27 17:15:03Alright, Readme.md is updated! You'll now find a picture right after the description of the signals that connect to the JST connectors on a Macintosh 512K LB (630-0118). This should definitely make things a bit easier.This is really helpful information. Thank you. I will be starting to build my board this week. | |
| Posted by: pezter22 on 2025-04-27 18:01:04 I was just looking at the BOMW ROM-inator install instructions and it uses the same two pins as the RAM expansion card (pins 45 and 46. So this would mean two wires connected with those pins. Just trying to make sure I get this correct. Thanks again for the new information. | |
Posted by: Builder68 on 2025-04-27 18:57:49I was just looking at the BOMW ROM-inator install instructions and it uses the same two pins as the RAM expansion card (pins 45 and 46. So this would mean two wires connected with those pins. Just trying to make sure I get this correct.Since these address bits from the CPU aren't connected anywhere else (on Macs 128K, 512K, and 512Ke), they are sourced from the single location where they exist. If you have concerns about having two wires (one for the memory expansion and another for the ROM-INATOR) connected to A17 and A18, please don't. There is nothing wrong with this; both cards require these input signals, and that's all. I strongly advise you to install the memory expansion card without the ROM-INATOR first. Reinstall your original 128KB ROMs from the Macintosh 512Ke. Once you have confirmed that the machine boots and the new memory size is fully detected, you can then begin the installation process for the ROM-INATOR. As I clearly stated in the readme.md file in the repository, the ROM_INATOR ROM image needs to be patched. Otherwise, the machine will freeze immediately after the "Welcome to Macintosh" window appears if the memory expansion board is installed concurrently. I have two sets of the ROM-INATOR ICs, one set is patched and the other not. I recommend that you do the same. I no longer have the ROM-INATOR board installed; instead, I installed the replica board of the MacSnap SCSI interface, made by Demik. Having the SCSI interface and the ROM-INATOR integrated into a single board would be the ideal solution to have both. | |
Posted by: pezter22 on 2025-04-28 06:04:40Since these address bits from the CPU aren't connected anywhere else (on Macs 128K, 512K, and 512Ke), they are sourced from the single location where they exist. If you have concerns about having two wires (one for the memory expansion and another for the ROM-INATOR) connected to A17 and A18, please don't. There is nothing wrong with this; both cards require these input signals, and that's all.Thankfully I have two Mac 512k boards. I was planning on installing the RAM expansion card on the one without the ROM-inator as a test. | |
| Posted by: pezter22 on 2025-05-03 09:52:35 I have all the components installed on the board. I just need to start adding the headers. I should be able to mount the PCB to the motherboard early next week. | |
| Posted by: pezter22 on 2025-05-03 14:09:32 Test fit. Very nice fitment! I just need to place headers on the board and then run jumper wires. | |
Posted by: Builder68 on 2025-05-03 14:25:42Test fit. Very nice fitment!Mmm... so, those ROMs you have installed—342-0220-B and 342-0221-B—are 64KB ROMs. We haven't tested the RAM Card with the Mac 128K/512K ROMs yet. | |
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