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Modern Power Supply for Macintosh II/x/fx
Posted by: chrisrueckert on 2024-12-26 10:32:31 What solutions are out there for the Macintosh II/x/fx series? I saw this https://www.instructables.com/Macintosh-IIfx-Modern-Power-Supply-Replacement/ but am wondering if there is a less complicated approach or solution.
Posted by: Unknown_K on 2024-12-26 12:33:25 Nothing modern fits without some "work".
Posted by: chrisrueckert on 2024-12-26 13:47:01 Nothing wrong about work... Just getting a more simplified solution would help tremendously. Like the ones that came up for the IIsi and LCs recently.
Posted by: Bolle on 2024-12-26 22:04:37 I just removed the internals of a dead IIfx power supply and got a random server psu from ebay to put inside the original shell. I drilled out the original standoffs and drilled new holes to add standoffs to match the hole pattern on the replacement. I didn’t bother putting a solution for the passthrough power connector back in place. In the guide you posted the passthrough will always be powered once the Mac is plugged in. The original power supply will switch the passthrough off when the Mac is powered down. That’s as easy as it gets without having to do 3D printed mounts and panels and all that stuff.
Posted by: Unknown_K on 2024-12-27 02:37:55 May I ask why you didn't try to fix the original supply (since you seem to be very technically inclined)? I kept some old dead custom PS supplies from OEM systems which I replaced because while just replacing them is cheaper now or at that time, down the road it might be worth fixing the old ones.
Posted by: jmacz on 2024-12-27 21:53:07 Same as @Bolle except I did get the passthrough power working by reusing the relay from the stock PSU. Don’t forget the power on stuff (the guide uses a transistor for this) if you want to be able to power up like stock (keyboard, etc).
Posted by: OleLila on 2026-09-08 13:00:42 Hello; I'm looking for advice regarding a power supply for a Macintosh IIx board. I do not have the old or a nonworking OEM power supply. I've looked at the link above but also would like to make do with what I have, and if I do buy, do not want to spend over 40 dollars or so. The OEM power supply is: : I have a nice standard size power supply. I do not mind that the standard power supply I have would be external to the case and see that it outputs 20 amps on 5-volt, however, this is a 750-watt power supply and it can supply 62 (sixty-two) amps on the 12-volt yet only 0.3 on the -12 volt. Will the board only take what it needs in this setting? Is 0.3 amps for the -12 enough? I was planning to use this adapter board between the power supply and the board and then putting to soft power circuit in the place of the on/off switch. I can have the power supply outside of the case and plug into this board on the inside. Really, really do not want to fry anything here; any advice, cautionary checks appreciated.
Posted by: Froggy814 on 2026-09-09 15:17:57 Does it plug power straight into the right pins of the connector. Or are you going to put the wires to where they need to go on the board through a custom made cable? Otherwise seems like a solid idea. Although I could be wrong.
Posted by: OleLila on 2026-09-10 17:33:55 Just going to put wire from terminals to board….the one that has my attention is the 12 volt that can supply 62 amps when the original power supply max on the 12 volt is 1 amp. Will it really just sit there and let the board max out at 1 amp?
Posted by: Froggy814 on 2026-09-10 17:59:56 You can always add an amp limiting circuit if you are worrying that much about it. And a voltage limiting.
Posted by: OleLila on 2026-09-11 08:59:25 Can I use this?...maybe place some type of load, set to 12 volts then short and set amp to maybe 1.2? On another note...what if I used 3 wall warts, reverse the leads on one to ge a negative 12 V, with closer specs and a single on/off switch?
Posted by: Froggy814 on 2026-09-11 09:28:12 I used something like that for my Portable... I don't know if anybody really knows though. You will just have to wing it and see what happens. Do a little research on how power works and viola. You can figure it out. Although I totally get the need for help. Make a mock up setup in paint and then ask. Then everyone can see the full setup you are looking at. That's my thoughts, you don't have to listen to them if you don't want to.
Posted by: ClassicGuyPhilly on 2026-09-11 11:56:29 Saw this on eBay this morning if a shortcut is desired 🙂 https://ebay.io/m/tYPsNB
Posted by: OleLila on 2026-09-11 14:15:01 ya..I saw that..just did it....overall costs more than I had hoped to get this system going but the vendor more than generous and have a proper power supply and can recap as needed. Will up date soon.
Posted by: OleLila on 2026-09-12 10:00:31 This is a thread that is full of information on power supply as well. https://68kmla.org/bb/threads/jmacz-mac-iifx-project.45083/
Posted by: Jockelill on 2026-09-17 00:33:46 It would be fairly easy to design a drop in board using sealed meanwell units. I have already designed one for the IIsi and one for the LC power supplies. Main reason I have not done for the IIfx is because I only have 1 PSU for them and it has already been recapped/repaired and working. But if someone in europe (preferably EU) has a spare broken PSU, I'd be happy to have a look at it 🙂 .The ones for LC and IIsi has worked really well, the only "issue" with these Meanwell units are that they are very stable at almost exactly 5.00V, 12.00V etc, wheras the original PSUs typically outputs slightly higher values (5.1V, 12.6 etc). This has the positive side effect of compensating for the sometimes rather high internal resistance on these older boards (the SE/30 is quite terrible in that sense). I don't know if that is also the case on the II/IIx/IIfx, but I would not be surprised if that was the case. So, a new, mean well based design, may or may not be a success on these boards. For the IIsi and LC this has really been a none issue, but still worth mentioning. Otherwise going the server ATX PSU route like @Bolle did is a very wise path 🙂 .
Posted by: Renegade on 2026-09-17 01:28:39 But if someone in europe (preferably EU) has a spare broken PSU, I'd be happy to have a look at it 🙂 I have a few of these power supplies lying around in my junk pile, and I think one of them might be defective. If you're not in a hurry, maybe I could help you out with that someday.
Posted by: Jockelill on 2026-09-17 02:09:10 I have a few of these power supplies lying around in my junk pile, and I think one of them might be defective. If you're not in a hurry, maybe I could help you out with that someday. Sure! Nah, no hurry at all, will be on the long list of todo anyway 🙂
Posted by: johnnyilblasco on 2026-09-17 04:13:16 Hi everyone, same problem here. I’ve been looking for a replacement for quite some time, but even among server power supplies, it’s not easy to find one with a 5V, 18–20A output. Do you have any suggestions? I had a solution similar to @Bolle ’s in mind, but I can’t seem to find a decent replacement. Would it make sense to use two power supplies together? A 5V 100W one and a 12V one, plus an isolated DC-DC converter for the -12V rail? Needless to say, with this solution, the startup circuit would need to be redesigned...
Posted by: Renegade on 2026-09-17 05:26:30 Sure! Nah, no hurry at all, will be on the long list of todo anyway 🙂 Don't hesitate to DM me when the time comes.
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