68kMLA Classic Interface
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| Reverse Engineering the Macintosh LC III Logicboard | |
| Posted by: marciot on 2022-03-17 22:01:54 I probably ought to start a new thread for my LC III board from hell, but here is my survey of all the potentially corroded traces on my board. The more I dig into this, the more daunting it looks! The number of broken traces now numbers about fifty 😯 All the traces which pass through the damaged area near the battery are painted in white. I came up with this by using GIMP's magic wand tool to trace the paths from the PNG files. Now have a GIMP file with 50 layers, one for each trace and I can use this to figure out where to place wire bridges to hopefully avoid the damaged traces and vias. Anyone want to call the odds of me actually being able to get a bootable computer from this board? @max1zzz, if I fail in this insane repair endeavor, I might have to buy one of your brand new boards! 😁 View attachment Damaged Traces.png | |
| Posted by: Trash80toHP_Mini on 2022-03-18 07:50:11 max, did you change your GAL setup? Looks like you condensed three smaller GALs into that one higher capacity GAL? | |
| Posted by: marciot on 2022-03-18 10:12:50 @max1zzz: How much you are selling or planning to sell your PCBs for? Do you use JLPCB assembly to prepopulate any of the smaller passive components or must these be carried over manually? What type of tools do you need to transfer the components? I have a hot air rework station, but not much experience with it, and I worry about hand soldering small pitch parts like the CPU and transferring the large plastic parts such as the memory slot and the PDS slot connector from one board to another. Is that a relatively easy job? | |
Posted by: max1zzz on 2022-03-18 10:42:40max, did you change your GAL setup? Looks like you condensed three smaller GALs into that one higher capacity GAL?Gals? There aren't any GAL's in these guys, it's all apple customs @max1zzz: How much you are selling or planning to sell your PCBs for? Do you use JLPCB assembly to prepopulate any of the smaller passive components or must these be carried over manually? What type of tools do you need to transfer the components? I have a hot air rework station, but not much experience with it, and I worry about hand soldering small pitch parts like the CPU and transferring the large plastic parts such as the memory slot and the PDS slot connector from one board to another. Is that a relatively easy job?The boards are £35 + shipping The boards come without anything pre populated (I did look at it but it was going to add ~£40 to the cost of each board which I didn't think was worth it, I can however generate the PNP data if you want to order some boards and go that route) Personally I move everything that is undamaged across and then replace anything that was damaged A soldering iron and hot air station is all that is technically needed although some form of good magnification will help too (I assemble the boards under a microscope 🙂 ) I can't say it is a easy job though, the memory controller in particular is a pretty fine pitch chip and is very easy to bend pins on and the PDS slot is a right pain to remove (The PDS connector can be replaced though, you can buy 2 96pin Din 41612 connectors (Or one 96pin and one shorter one) one connector fills the main section and then you can cut the last 6 rows off the second and use that to fill the smaller section) I can assemble the board for you if you decided against assembling it yourself, this service is £50 (with a 1-2 month lead time) There is a thread in the trading section too 🙂 https://68kmla.org/bb/index.php?threads/fs-reproduction-macintosh-lc-lc-iii-logicboard-pcbs.39812/ | |
Posted by: mmu_man on 2022-03-18 11:15:47The board layout, Gerbers, Copper layout and board scans are now available!Yay! | |
Posted by: Trash80toHP_Mini on 2022-03-18 21:20:05Gals? There aren't any GAL's in these guys, it's all apple customsMy bad, I confuzzled the pair of square ICs in that package type and the larger one "above" them. But was looking at the board from opposite directions it seems. They're still there and the larger package is still on the opposite side of the board. 😳 | |
Posted by: demik on 2022-03-22 06:50:59The board layout, Gerbers, Copper layout and board scans are now available! Thanks for releasing this, that's awesome ! | |
| Posted by: Trash80toHP_Mini on 2022-03-25 20:24:55 Facepalm if I haven't mentioned this? Long ago uniserver removed the built in memory of his LCIII and installed 8MB on tits pads. IIRC he said it could address more than that, but such wasn't available in a matching footprint package. I'll have to try to dig up that old thread sometime. So anyone building one of these new boards should source an 8MB set of chips. 😉 | |
| Posted by: max1zzz on 2022-03-26 10:28:08 Ooh so if I run some more address lines I could maybe get 4mx4 chips working for 16MB onboard. This might call for some experimentation! | |
| Posted by: mmu_man on 2022-04-29 18:58:47 Btw, having seen this thread about C22, I just confirmed mine has the + pin of C22 at -5V, which is not really a good idea. It still works but it will probably shorten its lifespan. Not sure what it would do to tantalums either… | |
Posted by: Trash80toHP_Mini on 2022-04-30 15:50:55Ooh so if I run some more address lines I could maybe get 4mx4 chips working for 16MB onboard. This might call for some experimentation!Glad thread opped up again. Have you looked at the possibilities yet? I'd think replacing the Bank A with a SIMM Slot makes more sense than any soldered memory config. BTW, where are my IIcx trace layer references? 😉 | |
Posted by: max1zzz on 2022-05-01 03:30:41Btw, having seen this thread about C22, I just confirmed mine has the + pin of C22 at -5V, which is not really a good idea. It still works but it will probably shorten its lifespan. Not sure what it would do to tantalums either…I have seen that, electrolytics and polys seem to be "ok" with the reverse voltage but it probably isn't great for them long term. Tants I would install the correct way round as they tent to short (and sometimes explode!) with reverse voltage Glad thread opped up again. Have you looked at the possibilities yet? I'd think replacing the Bank A with a SIMM Slot makes more sense than any soldered memory config.Not had a chance yet, way to many projects I need to finish off...... Though I have just tried out a new method of creating kicad layouts from the sprint layouts that is much faster than totally redrawing the boards form scratch so some playtime for the LCIII board is coming soon 🙂 (Just need to finish the schematics for it first....) BTW, where are my IIcx trace layer references?Ohhh yeah I forgot about that, Will try and remember to do that tonight! 🙂 | |
| Posted by: max1zzz on 2023-01-04 15:32:24 A quick note for anyone who might have had one of these boards made: I have discovered a error in the layout which stops accelerator cards form working in these boards (And possibly PDS cards that try to do DMA), there is a resistor on /BR of the onboard CPU that should be a pull down but is actually connected to 5V, this error prevents a accelerator card form being able to request the bus from the onboard CPU and makes the machine crash immediately This dose not affect the machine normally and will not cause issues with many PDS cards. The issue can be easily fixed by desoldering the end of R60 closest to the PDS connector, turning it 90degerees and adding a jumper wire from the resistor to ground | |
Posted by: djhaloeight on 2023-02-02 08:26:16A quick note for anyone who might have had one of these boards made:Haven’t had any issues with my board and the PDS ethernet card I use. 🙂 | |
| Posted by: theirongiant on 2025-02-07 09:15:53 Bumping this thread to say: this is amazing work. And also to ask: is there a schematic for the LC III in a PDF format? I'm doing the recap, and need to check where C5 and C7 go. The contact pads delaminated unexpectedly while cleaning and wicking them. | |
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