68kMLA Classic Interface
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| 128/512/Plus 240 V PSU Schematics | |
| Posted by: cheesestraws on 2021-09-08 14:23:33 I know a number of folks have been here wrangling 240V Pluses/512s/128s recently, myself included. Schematics for the 120 V version of the power supply are reasonably available, notably in Thomas H. Lee’s commentary on the design. However, the 240V version is laid out differently enough to be disorientating, and the component designations are totally different, and schematics do not seem to exist. So I spent a couple of afternoons drawing them out, more or less, and I offer them here for people's edification and delight. Fortunately, the 240 V PSU is extremely similar (perhaps unsurprisingly) to the 120 V one, so I have laid out the schematics and split them up in the same way that they are split up in the document linked above; that way, the text and diagrams in that document should be able to act as a guide to roughly what the 240 V one is doing, also. Figure numbers in my schematics correspond to figure numbers in that document and cover the same parts of the circuit. Note, please, though, that I do not wrangle power supplies professionally, nor am I strictly speaking within my comfort zone here. I have checked this information twice, but please verify anything important yourself with measurements on your own board if in doubt. Images are here: PDF is attached at the bottom of the post, or at the semi-stable URL https://windswept.home.blog/2021/09/08/macintosh-128k-512k-plus-240-v-power-supply-schematics/ Please feel free to copy, save, archive and distribute as helpful.  Input, rectification and filtering.  Feedback control circuit  Switching converter core  Output and crowbar circuit | |
| Posted by: Cinan on 2021-10-03 18:17:11 Yes I did and great work. I think my problem is back at Figure 2 of the original doc though re the horizontal sweep and high voltage circuit. | |
| Posted by: michimartini on 2021-10-10 11:27:01 Thanks for your effort - it inspired me to redraw it in Kicad. And in doing so I caught a few errors in your drawing as well. Attached is an archive of my kicad project in case someone wants to improve on it and then there's a color and a b&w PDF of the schematic exported from Kicad. There are also two PNGs that are annotated versions of your handdrawn schematics where i point out where you got it wrong. | |
Posted by: cheesestraws on 2021-10-10 12:12:00Thanks for your effort - it inspired me to redraw it in Kicad. And in doing so I caught a few errors in your drawing as well. Oh, wonderful. And thankyou for your corrections, also—I was really hoping someone would double-check me—I'm surprised I didn't get more wrong than that! | |
| Posted by: michimartini on 2021-10-12 06:51:49 Sorry, there was an error: C22 was a duplicate of C34. Fixed in this version. | |
Posted by: cheesestraws on 2021-10-12 07:55:56Sorry, there was an error: C22 was a duplicate of C34. Fixed in this version. Do you mind if I mirror these attached to my blog post in the initial post? (credited, of course) | |
| Posted by: michimartini on 2021-10-12 08:58:03 That would be great. Here is the complete archive again - now with the C22 fix included. The uncluttered version is without the dotted lines. | |
| Posted by: DarwinNE on 2024-07-27 14:39:48 Hi! I just wanted to say that I'm currently repairing my Plus, it is a 240V version and being able to work on the schematics that match it is extremely useful. Thank you for the amazing work! | |
| Posted by: cheesestraws on 2024-07-27 16:46:49 Glad they were useful! | |
| Posted by: DarwinNE on 2024-09-09 12:11:13 Hi again, I could use the schematic again and I noticed a small typo in the Kicad version: C26 should be 1nF instead of 100nF. | |
| Posted by: mitchW on 2025-12-20 15:46:55 Hey can anyone please provide me with the value for the R36 NTC inrush thermistor? Thanks | |
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