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Putting an ATX Power Supply in an 8600 or 9600
(or Making PS Connections for an 8600 or 9600 Motherboard in ATX cases)
by Dick Moore
Published 1/16/2001

    Disclaimer/Warning: This page is for entertainment only and is not guaranteed accurate. Performing modifications or other work inside your Mac will void your Apple warranty, may cause damage to your computer or result in personal injury. Although Dick indicates he made these modifications successfully, neither the site publishers nor the author warrants any of the information listed here. The modifications listed here are beyond the capability of most end users and all repairs or mods should be made by qualified computer technicians. The author and site publishers DO NOT recommend attempting any of the mods listed here. You assume all risk from the use of any of the information in this article.

First, anyone considering these conversions should first read all of the previous articles on the topic here at Mike's great site. Dan Calhoun got the ball rolling with a ton of valuable info [See the 8500 to ATX Case Conversion article-Mike]. When the power supply in my 8600 started acting up (at least I was pretty sure it was the supply -- the system would just suddenly and randomly power down), I began to think about using an ATX supply that I already had -- I just couldn't see paying nearly $200 for an Apple supply when PC units are so cheap. I didn't see any big problems except maybe for the extra wires found in the 8600 -- what equivalents, if any, would be needed with an ATX supply? I also was concerned about the power delivery of the 250W ATX. The 8600 & 9600 have big 390W supplies.

Enough power?
I was pretty sure that some capacity of that big 390W supply was just going to waste, at least in the 8600 -- maybe in the 9600 with six PCI slots, the extra power could be needed (but I don't really think so -- and I'm certain a 300W ATX supply would be ample). I knew from running all of my equipment in a Power Computing PowerWave 150 equipped with a 250W ATX supply as standard equipment that a 250W supply was up to the task. I have a G3 ZIF module in an XLR8 CarrierZIF daughtercard, a Zip drive, CD-ROM drive, floppy, CD-R burner, 9GB UW HD w/ an OrangeMicro Grappler 327 PCI controller card, an OrangeLink USB/FW PCI card, and an ATI PCI graphics card -- and the PowerWave has never once complained or run hot. Why not use an ATX supply rated for 300W or more? If I'd had one, I probably would have. Based on experience, I decided to go ahead with the 250W unit I had on hand.

What about extra wires?
As to the extra wires, I took the 8600 supply apart and looked on the two PC boards for the wire IDs. The only wires that weren't also on the ATX supply were a sense wire for the 5V supply (Green) and a pair of sense wires for the 3.3V supply (White and Brown). Going the other way, the Macs don't use the White 5V line in an ATX supply, and they also don't use the Gray Power Good line found in ATX units. If the ATX supply needed the Power Good line, I could use a pin on the 8600 motherboard, like the 5V sense pin (but it didn't). [See Diagram]

The no-splicing solution
Looking at the connectors, the 8600 uses two connectors which are more-pin (24) and fewer-pin (10) versions of the stock ATX 20-pin connector. [See Diagram] That meant that I could pull the socket pins/wires out of the two 8600 supply connectors and the ATX connector, and put the ATX supply pins/wires into the 8600 connector shells. This eliminated the need to do a bunch of messy wire splicing. I did have to figure out how to get the pins out. An extractor tool costs $25, so I wanted to find another way. I have a stainless steel pick I with a mostly straight tip (it has a little dog leg in the end from being used to ream things out) that was just right. I could slide the tip in along one side of a connector socket pin (see picture) and spin the point, then repeat on the other side, while pulling on the wire, and it would come right out.

When you're ready to put the connector pins/wires into the other connector shells, make sure that the little retaining wings on the pins are sticking out a bit -- sliding an X-acto knife blade under each wing and bending a little will put it right. Since I was stripping the 8600 supply for parts, I just left the Violet Power-on wire in the smaller motherboard connector and cut it off at the supply end, to use for the input to the add-on power-on inverter circuit.

Testing the ATX supply
Before putting the ATX unit into the 8600, I tested everything out. I built a little power supply load out of a male PC board connector with two .050" square pins on .3125" centers (the one from my junk box had two pins 5/8" apart which worked OK) and a 3.8 ohm 20W resistor soldered to the two pins. The .050" square pins are identical to the ones on the motherboard connector. You can buy a similar tester from CyberGuys for about $13.

This let me load the ATX supply enough to test the voltages and signals on all the connections. Switching-type supplies won't run correctly without sufficient current draw by a load -- usually one Amp is enough. With the load connected, I verified that the supply would start up when the Green Power-on wire was grounded. The Gray Power Good wire didn't seem to need to be connected to anything for the supply to run. I tried grounding it and connecting it to the 5V supply, but neither connection made any difference in operation. I just put heat-shrink tubing over it and also some over the White 5V line (not used by the Mac) and trussed them up alongside the other ATX wires. I took one black wire from the ATX supply and connected it to where the black wire had been in the 8600's smaller connector. This probably isn't necessary -- all of the Black wires are connected together, both on the motherboard and in the 8600 supply; I think this wire just provided a 5V sense line/common return with relatively low current flow for zero voltage drop in the wire.

Inverting the Power-on line
I did need an inverter circuit for the Power-on line from the 8600 motherboard. This line goes high when the power button is pushed, and it needs to go low for the Power-on line in the ATX supply. Dan Calhoun used a 74LS04 IC to do this. [Previous article - see Related Links below-Mike] I realized that if I used a 74HCT04, I wouldn't need any resistors or other parts; just the IC. If you use the LS version or any non-CMOS version of the 7404, you will need the resistors Dan shows in his circuit. I used a wire stripper to pull the insulation apart a tad on the Violet Standby wire and the Black Ground wire going to the smaller connector, and soldered pins 14 and 7, respectively, of a 14-pin IC socket to these two wires; again, no splicing. Just cut off adjacent IC socket pins so they won't contact the soldered connections. I cut the Green Power-on wire from the ATX supply to length and soldered it to pin 2 of the IC socket. I cut the Violet Power-on wire from the connector to length and soldered it to pin 1 of the IC socket. After making the four solder connections, I put the IC in the socket (be sure you know which pin is pin 1 on both parts) and then wrapped it all up in a piece of Gaffer's tape for insulation.

Metalwork The pictures show how I physically mounted the ATX supply in the 8600 chassis. I used shears to cut the steel rear panel of the 8600 power supply chassis off, to use it as the mounting panel for the ATX unit, since it already had the right holes for mounting in the computer chassis and it also had the fan holes. I had to drill the mounting holes for the ATX supply and enlarge the holes where the power connectors were, to fit the ATX connector arrangement. A piece of .093 aluminum sheet would be excellent for this also, since it is easy to cut and drill. You also could use .062 steel sheet. Or use .062 aluminum sheet, but you might have to prop up the back end of the ATX supply to relieve the bending moment on the thinner aluminum panel.

8600 / 9600 boards supply connections in an ATX chassis
Read the comments from the other articles about the various fit and metalwork issues. [Related Articles list below.-Mike] I've done it with a PowerCurve board and it was a bit of a hassle. The issue I want to discuss is making the supply connections. You can take out the ATX supply socket pins/wires and re-insert the Red, Black, and Orange wires into the original ATX connector to match the 8600's connector arrangement. BE CAREFUL -- the ATX shell is four pins smaller than the 8600 motherboard connector. The connector shells have plugs with two shapes -- square and barn-like, to prevent misalignment of connections. This means that when the ATX shell fits into the 8600 motherboard connector, it is going to be four pins short at the 3.3V wire end, and the connector latch isn't likely to work. This is not a problem, since the ATX 3.3V supply has three Orange wires, not eight, and you have four spaces in the shell.

The easiest way to get a smaller 10-pin connector is to scrounge up a dead ATX supply from a local computer shop. Believe me, they'll have some. Pull the socket pins/wires out of the shell, then trim down the shell to a 10-pin size (see my diagram). Again, BE CAREFUL to observe that the shell's individual plugs have two different shapes. Make sure that the shapes of your 10 pins mate with the smaller motherboard connector. Starting from the pin 1 end as shown in my diagram, cut the ATX connector shell in two, crossways, through the middle of the pins 6 & 16 section, then trim the 10-pin section with a razor knife to fit into the motherboard connector. Things will line up, although the connector latch won't work -- no biggie.

It works
The overall result is just fine. Everything works, and my 8600 has come back to life, for use by one of my sons. Plus I've got lots of great spare parts. The whole thing took about four hours of spare time. It'll take you less, since you won't have to test the hypothesis. Metalwork is the most time consuming for me. Enjoy!
-Dick Moore


Related Articles:

For other upgrades, mods, etc. see the main Systems page, CPU Upgrades, IDE, SCSI, Firewire and Video/DVD/Graphics Cards topics pages.


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