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Golfleep's 4790K mini-ITX iMac G4

Joined
Apr 28, 2015
Messages
78
Motherboard
Asus Maximus X Hero
CPU
i9-9900K
Graphics
Vega 64
The Finished Build
IMG_3151.jpg

After putting together a video editing hackintosh earlier this year, I’ve been wanting to put together a second hackintosh to serve as a render node for Final Cut Pro X distributed encoding. I had been planning on a mini-ITX build to keep the form factor small. In the process of looking at mini-ITX boards on various forums, I stumbled on several threads in this forum with iMac G4 case mods, and was intrigued by the ingenuity and creativity I saw in the different approaches to the case mods. Since I still had a 17” iMac sitting the closet which had died several years ago, I thought it would be fun to see if I could squeeze a maxed out socket 1150 build into the iMac G4.

This list is by no means inclusive, but some of the threads/websites that were helpful:

Thanks to all the contributors of the various threads in this forum, which made it much easier to complete this build

I knew power and cooling would be the main limiting factors in how fast of a setup I could squeeze into the half dome of my G4 iMac, and that things like keeping the PSU completely internal and maxing my 4790K overclock to 4.8 GHz, would probably be unrealistic goals. I also knew that aspects such as cosmetics or preserving the DVD drive would probably have to be sacrificed in order to getting the fastest components into the build:

Major Components


OSX Yosemite via Clover bootloader

iMac Monitor
When I had shelved the iMac six years ago, the monitor would not wake from sleep and was getting dim. For those that might need a little help with the tear down, this service guide might come in handy. Dremeljunkie's website and mactester57's thread were invaluable in helping me to successfully breakout the iMac’s video and inverter connections.

I initially used the Molex right angle DVI PCB connector 74320-4004 as suggested in dremel junkie's guide. However I eventually found and used a straight version of the connector 74320-5004, as I felt it gave a more streamlined connection and allowed everything to be more inline.

IMG_1511.jpgIMG_3120.jpgIMG_3122.jpg

Once I confirmed the monitor was working properly, the power connections for the inverter board were terminated with molex connectors, instead of using the alligator clips during the testing phase. The 3.3 volt and ground wires from the DVI connector above were combined with the 3.3 volt and ground wires for the inverter, the VEDID from the DVI connector was also brought over and spliced with the red inverter wire. The purple wire was left floating. I also chose not to enable monitor dimming as described in mactester57's thread, so the green wire was connected to 3.3 volt. The monitor is seen as a built-in display under OS X:

iMacDisplaySystemReport.jpg

Mockup & component fitting

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I used cardboard mockups to narrow down the setup and to see what would fit. I initially had hoped to keep everything internal but with the priority being CPU performance, I knew I would need a PSU that could deliver at least 250watts, which pretty much ruled out the picoPSU’s. I ended up going with HD Plex 250 DC PSU, knowing that it would to require me to use an external 19v AC adapter. The HD Plex 250 is rated at 250 watts continuous/400 watts peak, so I knew I would have some headroom to overlock my 4790K.

The mockups also allowed me to test fit different CPU coolers. Both the Noctua L9x65 and Dynatron K-666 fit well, but when I bench-tested the CPU coolers in open air, the Dynatron gave me the lower temps (but was noisier). All of the CPU coolers came pretty close to the opening of the faraday cage dome. There was still room for a Noctua 92 x 14 mm fan, but it required me to come up with new fan mounting brackets as the original iMac fan brackets were designed for a 25 mm thick fan, which would prevent the CPU cooler from fitting.

Baseplate modifications

IMG_3091.jpgIMG_3137.jpg

I trimmed the baseplate to allow the PSU to sit as low as possible, which it turn would maximize the room between the top of the CPU cooler and the 92 mm case fan. The motherboard was elevated about 25 mm off the baseplate floor with standoffs that I mounted into tapped M3 holes in the baseplate. A few small sheets of aluminum were added below the trimmed baseplate to support the PSU. The sheets were positioned carefully so that the outer base cover would still fit.

iMac motherboard and rear I/O modifications
In order to keep the iMac rear I/O panels, most of the original motherboard was trimmed off other than what was needed to mount the rear ports. After cutting the motherboard, the ports that were going to be rewired were removed with a heat gun.

Speaker jack

The original speaker jack was retained so that the original iMac speakers could be used. The output of the amplifier board (more details below) was wired to the pins as shown, this information was found in mactester57's thread listed above.​


IMG_3036.jpgIMG_3064.jpgIMG_3065.jpg

USB 2.0 Ports
The 5V and ground pins of all three USB ports are internally bridged. In order to separate them out, the motherboard was drilled out at the PCB mounting points. This allowed room to solder on short USB extensions (made from old USB cables) in order to extend the mini-ITX motherboard USB ports to the ports on the rear of the iMac.​

IMG_3070.jpgIMG_3071.jpg

USB 3.0 Port
The two firewire ports next to the USB 2.0 ports were also removed, and in their place, a short USB 3.0 extension cable was glued to provide a USB 3.0 port on the iMac's rear I/O.

Ethernet Port
I initially though I would be able to use the original ethernet port by simply soldering an extension onto the pins, but I quickly found out during testing that the original motherboard only supports 10/100 ethernet. Just like the USB ports, several of the ethernet jack pins were bridged within the motherboard, which disabled gigabit ethernet. Like the USB port, I had to pull the ethernet jack from the motherboard, drill out the PCB mounting area and then solder the extension directly to the pins. This enabled functioning gigabit ethernet.

Power switch
Use of the iMac's original power switch was retained. A front bezel wiring kit was used to provide the motherboard board connector and wiring. The wires were soldered directly to the PCB connections of the power switch on the original iMac motherboard.

DC Power Jack
The final I/O modification was for the 7.4 mm DC jack for the HD Plex 250 PSU. The old modem port was the perfect size for the DC jack. Even better, the phone jack is mounted to a separate small PCB, which made it easier to modify to hold the DC jack. I did have to use a bit of epoxy to make a spacer to prop up the DC jack to line up with the I/O panel of the iMac.​


IMG_3100.jpgIMG_3098.jpgIMG_3102.jpg

HDPLEX PSU, Amplifier, and SSD Mounting
The PSU, amplifier board, and SSD were all mounted underneath the motherboard. The PSU was mounted so that it's connectors would be clear of the motherboard, in order to keep things as vertically compact as possible. A small 5V laptop fan was mounted to direct airflow over the heatsink of the PSU. The amplifier board is a 2 x 3watt board based on the PAM8043 chip. Initially, I had background noise issues that were probably due to grounding issues. This was resolved by grounding the amplifier board as close as possible to the ALC892 chip in the motherboard - I ended up using the motherboard mounting screw right next to the ALC892 chip. (see below)

IMG_3107.jpgIMG_3117.jpg

WiFi and Bluetooth antennas
The iMac's built-in antenna connectors were not compatible with the standard antenna connectors, so a pair of laptop antennas were used, the antennas were placed outside of the faraday cage, underneath the outer plastic shell of the iMac, with the wiring routed through the faraday cage in the same manner as the original wiring.

Trimming the PSU wires
In order to make things as compact as possible and to facilitate putting the two halves of the iMac chassis together, The ATX and CPU PSU wiring was trimmed and sleeved, so there wouldn't be any loops to contend with. Items needed to work with ATX connector wiring:


Final assembly
The mini-ITX motherboard sits directly on top of the PSU. You can see how the end of the PSU extends past the motherboard to allow the PSU connectors to fit it, and by shortening and sleeving the PSU wiring, things are much more compact.

IMG_3126.jpgIMG_3128.jpgIMG_3127.jpg

To simplify the monitor wiring, the inner white fan/wiring bracket was drilled out to let the monitor wires exit directly. A Noctua 92 x 14 mm fan was necessary because of clearance issues with the CPU cooler, this also meant the stock fan brackets would not work, instead I had to construct custom fan brackets from flat aluminum stock. With the custom brackets, the base of the fan sits flush against the the bottom of the video wiring bracket/fan holder. In the second picture, the finalized DVI/HDMI connector is in the bottom center and the (blurred) power connector is to the bottom left. The wifi/bluetooth antennas were routed and secured from one side of the chassis to the proximity of the motherboard wifi connections.

IMG_3119.jpgIMG_3130.jpgIMG_3131.jpg

Benchmarks

Geekbench score @ 4.8 GHz
4.8GHzGeekbench.jpg

Geekbench score @ 4.6 GHZ
4.6GHzGeekbench.jpg

All in all, I have been very satisfied with the results, and had a lot of fun putting together the build. I can run the 4790K at 4.6 GHz and keep CPU temps in the 75-80° range. I did have to resort to using a large and heavy external AC power brick, and I did lose use of the DVD drive. The CPU cooler I ended up using is a bit noisy as well. Nevertheless, because I was able to retain most of the original ports and use the original speakers, the computer looks pretty much like it did prior to the mods. Even better, it essentially performs the same as my other hackintosh, allowing me to perform distributed encoding tasks in about half the time as with a solo computer.
 
Joined
May 16, 2011
Messages
17
Motherboard
MSI P67A GD55
CPU
Core i7 2600K
Graphics
Gainward GTX460 GS
Mac
MacBook Pro
Classic Mac
Mobile Phone
Android
Very impressive, Golfleep!
I especially like the idea of stacking the components - and lifting up the mainboard, as most modders try to keep the mainboard as low as possible.
Would it be possible to make it a silent computer if the i7 was not overclocked? For me this would be a huge issue...

best regards,
Jascha
 
Joined
Apr 28, 2015
Messages
78
Motherboard
Asus Maximus X Hero
CPU
i9-9900K
Graphics
Vega 64
Thanks Jascha,

I had to come up with the idea of elevating the mobo because the HD Plex PSU was fairly long (150 mm), and there was no other way it would fit into the dome without putting it under the motherboard. As for a silent build, the Noctua L9x65 was almost silent at low speeds, and so could definitely get you pretty close to silent, but overclocking would definitely be out of the question, and one might have to use a slower i7 CPU (like the 4790S) is order to keep the fan speeds down.

Another idea I played with was trying to incorporate the faraday cage and chassis as part of the CPU heat sink, much like it is in the original mobo. On the orginal mobo, the CPU heatsink is connected via heatpipes to the external chassis, which has fairly heavy mass and probably works well as a heat sink assuming you can get the heat transported. Using the whole chassis as a heatsink and an appropriate CPU could keep things pretty quiet as well.
 
Joined
May 16, 2011
Messages
17
Motherboard
MSI P67A GD55
CPU
Core i7 2600K
Graphics
Gainward GTX460 GS
Mac
MacBook Pro
Classic Mac
Mobile Phone
Android
I had to come up with the idea of elevating the mobo because the HD Plex PSU was fairly long (150 mm), and there was no other way it would fit into the dome without putting it under the motherboard.
This brought me to the idea of maybe fitting a decent graphics card e.g. Gigabyte GeForce GTX 970 Mini ITX Overclocked under the motherboard - when using a slimmer CPU heatsink, like the Noctua L9i. But I don't know if there's enough height - since most cards need two slots.

Another idea I played with was trying to incorporate the faraday cage and chassis as part of the CPU heat sink, much like it is in the original mobo. On the orginal mobo, the CPU heatsink is connected via heatpipes to the external chassis, which has fairly heavy mass and probably works well as a heat sink assuming you can get the heat transported. Using the whole chassis as a heatsink and an appropriate CPU could keep things pretty quiet as well.
This is by far the most elegant way - I was thinking about the same thing for my (not yet documented) "long-term" build. Unfortunately I have only the 15 inch chassis, which has only one heatpipe connecting cpu to the faraday cage - and this seems to be not enough...
 
Joined
Apr 28, 2015
Messages
78
Motherboard
Asus Maximus X Hero
CPU
i9-9900K
Graphics
Vega 64
It would be pretty tight to squeeze a mini-ITX graphics card underneath the mobo, but it might be doable. The mini-ITX board can be elevated about 40-45 mm off the base plate before the I/O ports and the RAM (which are located on the edges of the board, and so have the lowest clearance as you start to elevate the board) started hitting things inside the dome. But it would be tight. You could probably cut out more of the baseplate, which gains about 3-4 mm of vertical clearance. Another thing I encountered clearance wise was the screws and backplate on the underside of the 1150 socket, which happened to line up with the heatsink on the PSU and which required me to shave the heatsink a bit (you can see it in one of the pics). I'm guessing you would use a PCIe 16x extension cable? Might be tough to route the cable since it would probably be as long as the edge of the motherboard.

Didn't know the 15" had only one heatpipe! I think it's definitely doable to incorporate the heatpipes and faraday into the heatsink, but it would have required more metal fabrication tools and skills than I currently have access to.

This brought me to the idea of maybe fitting a decent graphics card e.g. Gigabyte GeForce GTX 970 Mini ITX Overclocked under the motherboard - when using a slimmer CPU heatsink, like the Noctua L9i. But I don't know if there's enough height - since most cards need two slots.



This is by far the most elegant way - I was thinking about the same thing for my (not yet documented) "long-term" build. Unfortunately I have only the 15 inch chassis, which has only one heatpipe connecting cpu to the faraday cage - and this seems to be not enough...
 

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