After 5 years serving the vintage Apple enthusiast community, ThinkClassic has been marked for closure and is now in caretaker mode. Please see this thread for further information. Please direct any questions, comments and enquiries about the website, management and ownership to this thread.

You are not logged in.

#1 2017-03-03 09:33:14

From: UK
Registered: 2015-03-07
Posts: 72

Mac IIci ATX PSU Conversion

The PSU in my Mac IIci is dead. Rather than replace it with an equivalent older PSU (which I might still do if this doesn't work out), such as another one from a IIci/IIcx/Q700/PPC7100, I'm thinking I would like to convert an ATX PSU for use within the IIci.

Now, I've trawled the interwebs for information regarding this and found a variety of different resources of varying helpfulness. Two of the biggest issues I seem to have read about include the loss of softpower without a workaround (not too bothered by this) and an incompatibility with some of the voltage pinouts (no -5 on modern ATX PSUs). I'm not sure which if any of these is an issue for the IIci.

It's worth stating that I've not converted a PSU before, so the clearer the information provided, the greater the appreciation. A few questions I have for getting started include:

1) What is most likely to fit best within the IIci case with the least amount of modification - an ATX PSU, Mini ITX, etc?

2) Is there a good resource that provides a very clear pinout map of both the IIci/IIcx/Q700/7100 PSU connector AND the ATX connector?

3) Beyond matching the correct cables to eachother, what other things will I need to consider (e.g. grounding, ensuring the PSU remains on, etc.)? I've seen posts suggesting that without some sort of switch, the ATX PSU will power up and down without staying on.

Basically, I'm a complete noob regarding this and would appreciate some clear guidance if possible. Thanks in advance.


#2 2017-03-03 17:08:17

From: Bermuda Triangle, NC USA
Registered: 2014-05-21
Posts: 1,470

Re: Mac IIci ATX PSU Conversion

ImAn00b2, so I'll be watching with great interest. I did compile this in my my search, it may not all be clear, but you might not have found some of the links. The ATX -> Mac Gazette AKA: ATX LinksProject™ wink


#3 2017-05-12 04:19:24

Registered: 2014-05-15
Posts: 183

Re: Mac IIci ATX PSU Conversion

I don't know too much about the power supply itself, but the maybe the softpower behavior can be inferred from the startup circuit schematic?


#4 2017-08-14 22:35:50

Registered: 2015-01-07
Posts: 16

Re: Mac IIci ATX PSU Conversion

The ATX and the Macintosh power supplies each connect a Startup wire to * as a start up signal.   The problem is that one of them uses Ground (the Mac, I think) and the other uses 5V for *.   The solution is to add a cheap 5V logical inverter.   Use the 5V trickle line to power it.  Hook its ground to ground.   Then hook the input to the Power On Signal from the logic board and the output to the power supply's Startup wire.

I have been tempted to attempt this.   I bought a couple of inexpensive mini-ITX supplies, which nevertheless, have more capacity than the IIci's original supply (at least in specs.) and plan/hope to migrate the circuit boards in the mini-ITX supply into the IIci's power supply case.  Also plan to retain/graft the logic board power supply connector onto the new circuitry and add the necessary inverter circuit for soft power on.


#5 2017-11-14 15:19:48

Registered: 2017-11-03
Posts: 1

Re: Mac IIci ATX PSU Conversion

ejt wrote:

ImAn00b2, so I'll be watching with great interest. I used Male Extra compile this in my my search, it may not all be clear, but you might not have found some of the links. wink

Did you pull it off? I'd be interested to find out how if you did.

Last edited by Dilks (2019-08-04 12:54:58)


Board footer

About ThinkClassic

ThinkClassic specialises in the use, maintenance, repair, restoration and modification of vintage computers and peripherals.