20" iMac G4 NUC/AiO Ivy Bridge Mod: SUCCESS!

20" iMac G4 / NUC Ivy Bridge Mod

Updates:

I'm happy to report that all problems have been solved and the motherboard fit test was successful.  This is currently the method I would recommend for those that want a 20" Ivy Bridge Hackintosh version of this mod.  As I noted in my previous post, while I initially believed I would not go in the direction of the NUC board, its remarkably small size and simplicity made it by far the best candidate for this mod.

Original vs NUC/DVD - Front

In multiple previous posts I have explained the advantages of having the core elements (processor/motherboard) of the mod at the top of the dome where ventilation is best.  In my previous ECX mod, the board only fit with the optical drive because I did not use the native PSU.  Because I wanted to use the native PSU, I did not believe fitting the optical drive was possible, but with this board it looks like it is going to fit. (Although nothing is definite until this is completed).  This board fits into the slot left vacant by the 3.5" HDD (the mSATA is on the mobo itself).  It pretty much fits into the grooves in the drive chassis requiring no alternation.  For comparison, I have taken side by side photos of the original optical drive and HDD in the drive chassis next to the shorter new dvd optical drive and the NUC occupying that area.  The height is pretty much the same and there is amble room for the connectors to fit as well.

Original vs NUC/DVD - Top

Problem Solving:

With this fitting at the top of the dome, I should have even a little but more room for components than I did with my previous mod.  This is because, there are less port extenders needed and no SSD is required at the bottom of the dome.  It will still be tight, but I have some wiggle room to address the problems that I brought up in my previous post.  Taking them one at a time:

1) USB Ports: A 4 port USB Hub leaves me with only 1 spare USB port, but solves the problem.  The addition of another hub or a larger one is likely.  A USB port supplies the 5V to the PSU.

2) The Fan: The directional fan is connected to the heatsink and I did not want to remove it.  I also wanted to keep the case fan.  Apple's connectors and colors are completely backwards from industry standards (Black is 12V, Red is Ground and the fan out is a 3pin Male connector, not Female).  The fan is also somewhat loud and old, so I decided to replace it.  I bought a Antec 92mm fan that had a molex out (there is no case fan output on the board).  There is a sense pin that I won't be using.  Because I won't have software fan control, I got a model with a 3 speed setting.  I put it on medium to reduce noise and may extend the controller to the back ports or simply leave it on this setting.

Wide Input Pico PSU

While 12V are readily obtainable from the PSU, the problem is that the PSU is always on.  So, the fan will spin as soon as the computer is plugged in, no matter if the computer is on or not.  As the computer does not have any 12V out, I will have to use some kind of switch.  Luckily, the PSU comes natively with a "switch".  The PSU relies on the motherboard to downconvert 12V to 5V then feed 5V back to the PSU to turn on the 24V line that powers the monitor's backlight.  Although there are many other ways to do this, I went with an elegant solution using what I had available.  Keep in mind this is not the only peripheral that needs power.  The optical drive requires 12V and 5V in either a molex or SATA power connector.  Luckily, I had a very small 20 pin PICO power supply with a WIDE INPUT range up to 24V. (Not all PICO PSUs can accept 24V, may sure before you connect).  I spliced the PWR input to the Green wire of the PSU (24V) which connects to the Inverter Wires as well.  I connected the ground to a native PSU ground.  As this is a standard 20 pin ATX based PSU, it won't work without a motherboard unless you ground the On Pin.  I have it connected to a switch, but will likely just leave in a wire, allowing the PSU to turn on as soon as it receives 24V DC input from the native PSU.  This produces the necessary 12V and even a 5V and has both a Molex and SATA power cable out.  I connected the Molex to the Fan (you only need the 12V line and ground), and the SATA to the optical drive.  Now we the peripherals will only turn on when the motherboard itself is turned on.

PICO PSU powering the optical drive

The Bypassed Power Switch

3) Power Switch: I did not want to damage the board, so I simply threaded small wires between the onboard switch and its solder points.  I did this to the front right and back left corners.  This was then wired to the case switch at the bottom of the dome.  These can be easily removed in the future if this board is ever repurposed.  In addition this does not effect the functionality of the original switch in any way.

The case switch I use is from my previous mod. Modeling clay was used to secure a momentary switch directly behind the peg that protrudes from the back of the plastic power button on the back of the iMac dome.

4) Audio: I am sticking with the Turtle Bay USB Audio solution from my last mod.  This allows for a standard 3.5mm audio jack out and also supports a 3.5mm Microphone in.  I have it wired to the microphone in the LCD housing.

5) Bluetooth: I have not found anyone who has had success with any half height mini PCI-E that supports Wifi and Bluetooth with Mac OSX.  So, I am simply going to keep my very small USB bluetooth solution.

6) Optical Drive: I am using a DVD Burner that gets power via the PICO PSU discussed in #2.  The connection to the mobo is via a SATA to USB 2.0 adapter cable.

12V to 19V DC-DC Upconverter

7) Power: While the option of splicing the AC to the to the existing AC plug with the NUC's powerbrick is not a bad one, it is somewhat of a waste of the 180 watt PSU that already exists in the machine.  Not to mention that I'm already including a second PSU (which is really being used only as a downconverter here).  The NUC requires 19V at (at least) 3.7A and the PSU is only supplying 12V (can't use the 24V because its only on with 5V from the motherboard).  Luckily, 19V is the typical notebook operating voltage and therefore upconverters are available.  Though there is a much smaller selection than for more common voltages (24V, 12V, 5V etc).  Many different shapes an sizes are available.  I got one in a familiar shape on ebay from a Chinese manufacturer for $20.  Its relatively small ( I may remove part of the heat sink surrounding it) and is a 12V DC to 19V DC upconverter at 4A.  This is exactly what is required and works flawlessly.

The Upconverter connected to PSU and NUC

The Upconverter gets 12V and Ground in from the Native PSU and sends 19V out.  I had a broken Laptop AC power adapter that had a DC input that perfectly matched the power in plug on the NUC.  The positive is the inside peg and the negative is the outer part.  Using a multimeter I ensured which wire was which and connected this to the power supply via the up converter.

The Fit Test:

The Secured NUC Motherboard

On a side note, I used a rubber sleeve to cover the drive cage where the NUC will go.  After some guess and check, I determined the place where the  NUC and USB connectors seemed to fit the best. To test fit, I used twist ties that went through the screw holes in the grooves intended for the HD and then through the motherboard screw holes.  These will be replaced with plastic locking ties to secure the motherboard in place.
One thing to make sure of is that the wifi antennae which goes through the metal faraday cage (Wifi signal will be severely reduced if the antenna is within the cage) is connected to the wifi card before the board is secured.

Build Pics:

A Mess of Wires, But A Working Mod

Video and Audio Test

Motherboard View

About This Mac Screen

Remaining Issues:

Obviously, there is a lot of cable management to do.  This will get much simpler once connections are directly soldered (connectors removed and alligator wires eliminated).  As I technically have more room at the bottom of the dome than the previous mod (also had a DC converter and a PICO PSU to deal with), I do not believe this will be difficult to fit.  The wire management, however, may be more involved.

There will a paucity of ports.  A 3.5mm audio out, a few USBs, and not much else.  If I had to do it over, I probably would not have bothered spending the extra money on the Thunderbolt equipped version.  There are so few available peripherals and there are so overpriced that I can not even test this. Perhaps this is somewhat future proofing, but I would imagine there will be further upgrades to this board before thunderbolt actually takes off (if it ever does).  That said, I would not have bothered with an ethernet extender anyway.  I've learned with this that the more you do, the more that can go wrong.  I am more than happy to keep it simple.  I also have the option of adding a powered USB hub with the 12V lines in the PSU.  Unlike my previous mod which was very close to its power maximum, this should have room to spare.

Concluding Thoughts:

Untili I have it assembled and have worked with it for a while, I'm cautious about speaking too soon, but I am very optimistic about this project.  Although to Core i5 Sandy Bridge to a Core i3 Ivy Bridge may seem like a lateral move, this board is simply a better fit.  Its lower power, quieter, and everything onboard works.  The incorporation of the native PSU while keeping the optical drive makes this virtually indistinguishable from the original 20" iMac G4.

Hopefully will finish soon! Thanks for reading.

The 17" iMac G4 Native PSU

Introduction

While I have not hooked the native PSU up to a mod and there is one wire that I do not understand the purpose of, I have checked all the collages of a working PSU.  I now know that is it similar in principal to the 20" PSU.  As this is all based off of my work with the 20", more information is available in that post:

The 20" iMac G4 Native PSU

17" iMac G4 PSU

vs ATX PSU

ATXPSU

The Native PSU is an always on, 12V only power supply.  Always on meaning that unlike standard ATX PSUs, the moment the AC cable is plugged into an outlet, there is DC power in the pins.  To get an ATX PSU to work without a motherboard, a pin in the motherboard connector needs to be grounded (known as "jumping" the PSU).

12V only means that unlike standard PSUs, only 12VDC and Grounds are supplied to the motherboard.   ATX PSUs transform the 120VAC in the wall to 12V DC and also downconvert the 12V to 5V and 3.3V.  These 3 different DC voltages are supplied to the motherboard in multiple rails via a 20 or 24pin connector.  Because the PSU supplies the iMac's motherboard with only 12V rails, the downconversion to 5V and 3.3V happen on the motherboard itself.

ATX PSUs also tend to supply peripherals directly, Molex, SATA power, 8pin PCIe etc emanate directly from the PSU itself.  As noted, ATX PSUs are not "always on", they have to be "jumped" either manually or by the motherboard.  As a result, the peripherals will not be given power until the motherboard is switched on, despite the fact that the power is supplied directly from the PSU to the peripherals.  Because the iMac's PSU only has 12V, the one molex line with 2 molex connectors (for the cd and hdd) emerge from the motherboard.  Although the molex wires share the same 16pin connector, it comes from the motherboard and does not interact with the PSU at all.  As the peripherals are supplied by the motherboard they will be off when the mobo is off despite the "always on" PSU.

The Connector

"Clip Side"

"Non-Clip" Side - All Grounds

The connector is 8x2 for a total of 16pins, one slot is empty for a total of 15 wires.  Of those 15, 4 (Yellow, Red, Black x 2) go from the main connector to the molex connectors.  Because we will not use of the original mobo, these wires connect to nothing and have nothing to do with the PSU at all.  That leaves 11 Power supply wires.  The blue wire seems to have no detectable voltage and grounding it does not seem to have any effect.  In the 20", the blue wire acted as the ground component (with a white wire supplying +5V DC to the PSU - the white wire is not found on the 17" - the pin is left empty) of a switch to turn on 24V DC supply to the LCDs backlight.

In the 17" the 24V Green line is replaced by an extra yellow +12V DC.  While I do believe this (similar to the 24V required by the 20" backlights) does go to the blue wire of the inverter to supply the power to the backlights, the "switch" to turn the backlights on works differently.  Here the extra 12V DC line is on as soon as you plug in the power cable.  This is the same as the other 12V lines.  No voltage needs to be applied to the PSU in order to get all the lines working.

So, I am not exactly sure the purpose of the blue wire.  Since, I don't have a working 17" mobo to even voltage test it.  I do have a theory, I believe it acts as a ground for a similar switch mechanism as seen in the 20", however, this switch (which also uses 5V) happens in the inverter itself, not the PSU.  I'll talk more abut this later.  For our purposes its really of no consequence.  What we are left with is 10 PSU cables, 5 Yellows and 5 Blacks.  This means there are 5 12V DC rails supplied to the motherboard, as soon as the iMac is plugged in.

The Pinout:

17" iMac G4 PSU Pinout

Please note this is an alteration of an image from my 20" pinout - hence the crude "photoshop"

Again I break it down into four zones:

1. Yellow Zone: Pins 1 - 4 and 9 - 12: 4 rails of 12V DC and grounds

2, Blue Zone - Pin 13 - The blue wire is the only pin (will not be used here)

3. Red Zone - Pins 6, 7, 14, and 15 - The molex connector comes out from here.  You will want to save the actual wires and connectors for use in this mod, but these pins are of no consequence.

4. Green Zone - Pin 8 and 16 - This likely is the 12V rail which the motherboard routes to the inverter, but since its automatically on and we aren't using the original mobo , its just another 12V DC rail with ground to us.

Getting a 5V Line:

The 2 plug connector connects to the AC port on the back of the iMac G4 which contains the C5 receptacle (The 3 pronged plug with 3 circles that resembles Mickey Mouse).  This plugs into the AC on the wall and there is +12V DC in our yellow wires.  In total there are 5 rails (Pairs of Yellows and Black Ground wires).  However, this mod calls for a molex adapter to be used as a PSU.  The molex adapter has a Yellow +12V DC rail and a Red +5V DC rail.

My switch theory (Optional Reading):

The 17" Inverter Pinout

For those of you that are familiar with the 20" PSU you may be aware that I mentioned in my post that a 5V line is not necessary to get the LCD working.  This is because the one place on the 20" that required 5V was "the switch".  This switch worked by the motherboard downconverting 12V to 5V then feeding it back to the PSU via the White/Blue wires.  The 5V turned on an upconverter (or possibly a transformer) that produced the 24V line.  +24V now flowed in the Green wire of the PSU, this went through the connector and got directly routed through the motherboard to the Blue/Red (+24V)  and Green/Black (as Ground) wires of the inverter cable.  When 24V reached the inverter the backlights turned on. On the 20", I used the 5V that came from the DVI cable.  As this is just a switch I was not worried about overtaxing the low current available in this line.  

For the 17" PSU, there is no switch involving the PSU.  The Yellow wire at the end (in the Green Wire's Place from the 20") is on as soon as it is plugged in.  However, I believe there is a similar switch mechanism, but it is in the inverter, not the PSU.  The 20" has 6 backlights, the 17" has 2 backlights, so I understand the need for (2) 24V lines and (2) Grounds.  In the 17" inverter cable there is (1) Ground and (1) Power Wire +12V via the Blue Wire.  Initially I thought that 5V was also somehow required to power the inverter, however after some experimentation, I realized the 5V required for the Red inverter cable acts as a switch and not as a true "power source".  Because of this, the Red Inverter cable can be connected to the DVI +5VDC power source.  Obviously this is similar to what I just described as the switch mechanism in the 20" iMac G4.

The 20" Inverter Pinout - Revised

Comparing the 2 inverter pinouts shows similarities.  The Orange (Dimmer) and Purple (Possible role in Sleep?) are left unconnected.  The 6 backlights in the 20" need two power rails, so both Blue and Red wires supply + current with Green and Black as their respective Grounds.  The 17" has 2 backlights and needs only one power rail, the Blue wire as + current with Black as its Ground.

In addition there is a Yellow in the 20" and a Green in the 17" that need very low current via Resistor connected to 5V.  This wire appears to be involved in wake from sleep.

All wires are accounted to except for the RED wire in the 17" inverter cable.  This wire uses 5V produced by the motherboard from downconversion of the PSU's 12V and uses it to "turn on" the inverter, acting as a switch.  This is exactly what the White Wire (which is missing from the 17" PSU) of the PSU does for the 20". Except it acts at a different location.  This also makes me think the remaining Blue Wire may somehow be a ground wire that the motherboard uses for this mechanism.  But, as we ground our 5V DVI Current via the DVI, it is not used.

Need for 5V and Preparing the PSU:

Although the inverter could probably all be handled by the DVI input (could likely get away connecting the Green inverter wire as well.  There is one more thing which requires 5V, the LCD itself.  The Gray cable of the LCD contains 3 wires which power the LCD screen.  In the 20", 12V is needed, but in the 17" 5V or 3.3V is needed.  As this is not just a switch, but actually powering something, I would not use the DVI source as you will likely overtax it.  This may actually damage your source, computer, video card etc.  So 5V must be created from the PSU.

At this point, I would recommend cutting off the motherboard connector to free all the PSU's wires.   Right above where the wires enter the connector cut them free.  This gets rid of the molex connector (you do not need the cut these 4 as they are not attached to the PSU itself).  You should be left with 5 Yellows, 5 Blacks, and 1 Blue (which will not be used) coming out of the PSU.

Option 1 - A computer in the base:

This is for how that are using some type of small form factor board i.e. Nano, Pico, or ECX.  Many of these boards are powered by a P4 connector.  This is a 4 pinned connector (2x2) that uses 2 - 12V and 2 - Grounds.  As there are plenty of 12V rails available from the PSU, simply take your motherboard power connector and attach the 12V DC lines to the Yellow wires from the PSU and the Grounds to the Black PSU wires.  In the picture of my KEEX-6100 below, the P4 connector can be seen in the front right corner of the motherboard.  This connector attaches to a 12V rail from the native PSU.

KEEX 6100 with P4 connector to Native PSU

The reason this will work is that this board (as well as several other small form factor boards) works just like the original iMac G4 motherboard in that it requires only 12V in to work and it itself has downconverters on it.  The KEEX-6100 actually has a mini-Molex/SATA power out port, which can be seen in the back, just left of the fan.  This gives a couple molex out, including 5V.  So you have a 5V line from here.  Just note that I would still recommend taking the 12V backlight power from a Yellow 12V rail from the PSU itself, but the LCD power and ground can connect to the Red 5V and Black-Ground line here.  The Green from the inverter can also go here or the DVI 5V as noted.

Option 2 - Use a second PSU - a PICO PSU connected to the native PSU

A PICO PSU with rocker switch

Almost all PICO PSUs use 12V DC input (some have wide ranges in DC input).  Power it by hooking a 12V line from the native PSU to the DC power in (the white and black wires pictured that hook up to the connector for an external power brick).  As the native PSU gives you 12V DC already, you do not need a power brick.  You must "jump" the PICO PSU in some fashion, depending on what your intended iMac G4 mod is.  The Jump mechanism can be "always on" with a simple wire or "on/off" with a rocker switch (as pictured) to control power out from the PSU.

If you are using a motherboard in the base that requires an ATX Power connector, this is without a doubt the way to go.  You can plug this into the motherboard connector, without having to wire all sorts of adapters and converters, at a negligible loss of space.  Of course if its connected to an ATX mobo, the motherboard will jump it for you.  

If you are using this for an external monitor with peripherals (ex. dvd drive), you can use the requirement to "jump" this psu to your advantage.  You can put a rocker switch here that will allow you to turn off everything its connected to.  Remember the native PSU will be on as soon as you plug it in, by jumping this psu without a switch, it will also be on.  Thus, drives will be spinning, leds will be glowing etc whenever it is plugged in.  With a switch here you can turn the whole unit LCD and peripherals completely off.  Just remember, no matter what wattage PSU you get, these are not additive, they are connected in serial, so you are still limited by the overall wattage of the native PSU.  Also, you have to make sure that the wattage is adequate for anything you have connected "downstream" of PICO PSU including the LCD power (though the backlights can be connected to either the native or PICO PSU).

The PICO PSU is probably the most flexible option as they are available with P4 connectors. molex connectors. SATA power connectors etc.  If you are not using an ATX motherboard, you could even use the power from the pins intended for the motherboard.  However its expensive and not needed if you use Option #1.  And if you aren't using peripherals requiring 5V - you can likely use the cheaper option #3.

Option 3 - Use a 12V to 5V DC-DC Downconverter

15W 12V to 5V DC downconverter

These can usually be found for around $5.  Connect one 12V and Ground in and you get 1 5V and Ground out.  Combine this 5V rail with a different 12V from the native PSU.  With a 12V and 5V rail, we now have our "molex wires" that acts as our power source.

All these are acceptable, as is using a different PSU altogether, it simply depends on your goals and needs.  As always - thanks for reading!!

20" iMac G4 - The Native PSU

20" iMac G4 LCD powered only by Native PSU

The Native PSU is not enclosed.  Once it is plugged in, it is live.  Please use extreme caution with both the Power Source itself and its wires.  Keep any conductive objects away from the PSU and do not handle either the PSU itself or make changes to its wires while it is plugged in.  As always, proceed at your own risk.

Background

C5 receptacle
Courtesy of Wikipedia

From the onset of my 20" All-In-One Sandy Bridge mod, it was clear that the native PSU was not going to fit (from both a physical space perspective and a heat generating perspective).  It was either the optical drive or the native PSU.  I kept the optical drive and used a PICO PSU instead.  This put most of the physical bulk and heat generation on the outside of the mod in the form of a power brick.  However, I certainly understand the draw of using the native PSU. First, a modder likely alread has one, its right there in the iMac, no extra parts need to be purchased (the cost can be substantial as high wattage Pico PSUs cost around $150).  Secondly, there is no power brick, the rear plug would house a receptacle for the rounded, 3 pronged C5 plug of the native iMac G4.  Third, and most importantly is that it was designed to power this display.  Because of this it has a wattage greater than any PICO PSU (190 watts) and has a 24V line for the display, eliminating the need an up converter or separate 24V source.

20" iMac G4 Native PSU

Connected to AC C5 Recepticle

The problem, or so I thought, with the Native PSU has been that it can not be "jumped" in a conventional manner.  "Jumping" is a technique used in conventional ATX PSUs.  Grounding (connecting to a ground wire) a particular pin in the motherboard connector causes the PSU to "turn on" in the absence of a motherboard and the momentary switch that the mobo provides to turn the psu and subsequently the computer and internal devices on.  A few intrepid readers have let me know that they have had success "jumping" by supplying 5V to a particular pin in the motherboard connector.  I had thought of this PSU as a variation of an ATX PSU, with similar properties.  The problem I had envisioned using this solution is I figured a separate 5V source, in the form of a second PSU would be needed to give 5V to the native PSU in order to "turn on or jump" the native PSU.  While this may have allowed for a low wattage second PSU, because you still needed a different PSU, it somewhat defeats the purpose of using the native PSU.  I was mistaken, at least for the 20" PSU.  This is not how the native 20" PSU works at all.  I did initially have a working PSU for the 20" (Side note: The PSU seems to have the highest failure rate of any iMac G4 20" part and has been almost universally dead on every non-operational 20" iMac G4 I have obtained), so I purchased a known operational PSU.  The one I bought is green and like everything with these computers, I have seen variation in the PSUs even between the same size iMac.  So, I can not say for sure that all PSUs will work like this one.

How Does It Work

"Clip" Side

The PSU doesn't really need to be jumped at all.  It is "always on".  Looking at the motherboard connector, one side (that has the motherboard clip on it) has 4 yellow wires, then a blue, then yellow and red that go to the molex, and finally a green wire.  The other side (without the clip) has all Black Wires except for one White Wire.

"Non-Clip" Side

To be honest, this PSU confused the hell out of me and I believed I had a defective PSU initially.  It was the Molex connector here that really threw me off.  To test PSUs, I have a Molex powered fan that also lights up.  I attach this to a molex connector from the PSU.  When I turn on a PSU, I expect to hear the fan and see the LEDs turn on.  This fan (like most) uses 5V, so it really only connects to the 5V lead (Red Molex) and a ground.  No matter what I did, I could not get the fan to turn on.  Of course, I could have supplied the 5V directly to the pin the fan was connected to, but that seemed ridiculous.  In truth, 5V being supplied to this pin is likely what happens with the native PSU/Mobo setup.  It wasn't until I tested the voltage on one of the (non-Molex) Yellow wires that I realized that the PSU was in fact live as soon as it was plugged in and the Yellow lines have +12V DC on them.  This PSU appears to be a variation of a "12V only" PSU (with one notable exception).  12V only PSUs rely on the motherboard for the DC-DC downconversion and most modern ones have 5V and 3.3V rails.  12V only PSUs are usually PSUs for low power boards.  It appears that the PSU supplies the motherboard with 4 12V rails in the form of the 4 yellow(12V) and black(ground) wire pairs.  This is similar to using a PCI-E 8 pin power connector (or 2 P4 power connectors).  The molex power actually emerges FROM the motherboard, 12V directed from the PSU through the motherboard out to the yellow molex and the 5V a result of the motherboard down converting 12V to 5V and sending that through the Red 5V wire.  So when I hooked the fan up to the molex, without a motherboard, I was in essence hooking it up to nothing.  It is pretty obvious that the molex wires come from the connector and not the PSU at all.  Initially however, I thought these wires might interact with adjacent wires within the connector itself, but this is not the case.  That leaves the green/black and white/blue wire pairs.

Looking at the motherboard side

The Green Wire (only on the 20") likely represents the only DC-DC conversion that the PSU does itself.  And its an up conversion from 12V to 24V (Though this could also be generated by a separate transformation from the AC current).  The Black wire that it is paired with is simply a ground wire.  There is no voltage detected when you plug the PSUs AC Cable in.  This is because the motherboard "tells" the PSU to supply the 24V rail only when its on.  The motherboard does this by supplying a +5V current to the White Wire with the Blue Wire acting as the ground in this circuit.

The PSU Pinout:

ATX PSU Pinouts

Naming Convention of ATX PSUs numbers from Right to Left, Top then Bottom, looking at the open pins (motherboard side) of the connector while the clip is positioned on the bottom.  I will keep this same convention for the pin numbers I use for the iMac G4s native PSU.

20" iMac G4 PSU Pinout

The pin numbers are identified on each pin.  I have also divided the 16 pin connector into 4 colored zones.


Yellow Zone (Pins 1-4 & 9 - 12): These 4 yellows and 4 black wires are on as soon as you plug in the PSU.  Each of the 4 Yellows (9 - 12) has +12V DC and the Blacks (1 - 4) are their corresponding grounds.

Blue Zone (Pins 5 & 13): These 2 wires form a powered switch.  By supplying 5V+ to the White Wire (Pin #5) and grounding the Blue Wire (Pin #13) the PSU turns on Pin #16, the Green Wire.

Red Zone (Pins 6,7,14,15): These 4 wires were used by the iMac G4 to power the optical and hard drives via 2 molex connectors.  The 12V for the Yellow and the 5V for the Red and 2 Black Grounds came from the motherboard.  As these are simply a molex cable hooked up to nothing, you can ignore these wires.

Green Zone (Pins 8 & 16): +24V will be supplied by the PSU via the Green Wire (Pin  #16), which is required for the backlights, when 2 conditions are met: The PSU is plugged in and the White/Blue (Blue Zone) Wires are supplying 5V, turning the the "Switch" on.  Pin #8 is the Black Wire Ground for the backlights.

Applying this to the 20" iMac G4 Mod

This will only make sense if you are familiar with my more recent TMDS to DVI iMac G4 mods.  In this case knowledge of the 20" iMac G4 mod in particular is recommended.  Click the link below for details:

All in One 20" iMac G4 Sandy Bridge Mod

and the iMac G4 20" Inverter Pinout:

Updated iMac G4 20" Inverter Pinout

I used a PICO PSU for this mod.  The PICO PSU has 12V rails, 5V rails, and 3.3V rails (the 3.3V rail is not needed for this mod).  In addition, I used a 12V to 24V DC-DC Upconverter to get the 24V rail required for the monitor.  To replace the PICO PSU with the Native PSU you need the PSU to supply 5V, 12V, and 24V.  As the native PSU has 12V working as soon as you plug it in, we have our 12V rail.  As noted above, if you supply 5V to the Native PSU, a 24V rail will be turned on, so 24V is taken care of.  This leaves only the need for a 5V rail.  While 5V is not actually needed by either the LCD or the backlights itself, you would need 5V for any device that is molex or SATA powered.  This includes hard drives, fans, optical drives, and even touch screens.

There are 4 basic ways to get 5V, which one you choose depends largely on what you intend to use in the base.

1) Use a second PSU - a PICO PSU connected to the native PSU

A PICO PSU with rocker switch

Almost all PICO PSUs use 12V DC input (some have wide ranges in DC input).  Power it by hooking a 12V line from the native PSU to the DC power in (the white and black wires pictured that hook up to the connector for an external power brick).  As the native PSU gives you 12V DC already, you do not need a power brick.  You must "jump" the PICO PSU in some fashion, depending on what your intended iMac G4 mod is.  The Jump mechanism can be "always on" with a simple wire or "on/off" with a rocker switch (as pictured) to control power out from the PSU.

If you are using a motherboard in the base that requires an ATX Power connector, this is without a doubt the way to go.  You can plug this into the motherboard connector, without having to wire all sorts of adapters and converters, at a negligible loss of space.  Of course if its connected to an ATX mobo, the motherboard will jump it for you.  

If you are using this for an external monitor with peripherals (ex. dvd drive), you can use the requirement to "jump" this psu to your advantage.  You can put a rocker switch here that will allow you to turn off everything its connected to.  Remember the native PSU will be on as soon as you plug it in, by jumping this psu without a switch, it will also be on.  Thus, drives will be spinning, leds will be glowing etc whenever it is plugged in.  With a switch here you can turn the whole unit LCD and peripherals completely off.  Just remember, no matter what wattage PSU you get, these are not additive, they are connected in serial, so you are still limited by the overall wattage of the native PSU.  Also, you have to make sure that the wattage is adequate for anything you have connected "downstream" of PICO PSU.

The PICO PSU is probably the most flexible option as they are available with P4 connectors. molex connectors. SATA power connectors etc.  If you are not using an ATX motherboard, you could even use the power from the pins intended for the motherboard.  However its expensive and not needed if you use Option #2.  And if you aren't using peripherals requiring 5V - it is way overkill and you should use Option #4.   I'd even recommend hooking up the White PSU wire using #4 and using the 5V rail from the PICO PSU only for peripherals because #4 works the best for sleep/wake.

2) Use a small form factor mobo that uses 12V only for power (ex KEEX ECX boards)

Many small form factor boards including ECX boards use a P4 connector.  This is a 4 pinned connector (2x2) that uses 2 - 12V and 2 - Grounds.  As there are plenty of 12V rails available from the PSU, simply take your motherboard power connector and attach the 12V DC lines to the Yellow wires from the PSU and the Grounds to the Black PSU wires.  In the picture of my KEEX-6100 below, the P4 connector can be seen in the front right corner of the motherboard.  This connector attaches to a 12V rail from the native PSU.

The KEEX-6100

The reason this will work is that this board (as well as several other small form factor boards) works just like the original iMac G4 motherboard in that it requires only 12V in to work and it itself has downconverters on it.  The KEEX-6100 actually has a mini-Molex/SATA power out port, which can be seen in the back, just left of the fan.  This gives a couple molex out, including 5V.  So you have a 5V line from here.  However, as above, I'd still recommend hooking up the White PSU wire using #4 and using the 5V rail here for other peripherals as #4 works the best for sleep/wake.

3) Also a 12V to 5V downconverter can be used:

The PSU circuit

AC Plug into the wall is transformed into 12V DC by the PSU and plugged into the motherboard supplying 4 12V rails to the mobo.  When the power/momentary switch is pressed the motherboard turns itself on, opens gates to downconvert some 12V current to 5V.  Power is sent from from the motherboard to the 12V and 5V rails of the molex wire to supply the drives.  Also 5V is sent in a circuit back to the PSU via the white wire and back via the blue wire.  This turns on a transformer or up converter on the PSU which then sends 24V via the Green wire to the LCD.

This is actually quite brilliant and remarkably simple.  This opens up several intriguing possibilities for future mods.  My first test was to add 5V via white/blue from an AC to molex and confirm 24V on green/black with multimeter.  I did not want to add a second PSU and I knew power was technically already flowing to the 12V rails, I simply mimicked the motherboard using a very small, inexpensive 12V to 5V downconverter.

15W Downconverter

The PSU circuit and how I created it:

I cut free from the motherboard connector these wires: (The grounds are interchangeable, I used the matched pair across for convenience)

12 to 5V DC-DC downconverter hooked up

1 Yellow/Black (NON-MOLEX)
The White/Blue
The Green/Black

The Yellow was connected to 2 wires:
   The alligator wire the comes from the 12V LCD wires in the Gray Cable of the neck (Purple, Yellow, and Orange).  I also connected this to the 12V input of the Downconverter.
The Black was connected to the Gray Cable of the neck/LCDs grounds (Blue, Green, Gray, and Pin 15 of the DVI).  I also connected this to the ground input of the Downconverter

The White was connected to the +5V out of the downconverter and the Blue connected to the ground out of the downconverter.

The Green was connected to the inverter cables Red/Blue (+24V) and the Black to the inverter cables Green/Black (Ground).  Turn in on and there is the video.

Native PSU and LCD reunited

4) The Best and Easiest Way using the DVI 5V Pin

Overview

Really the best and the easiest way to do this especially, if you don't need a 5V rail for anything except for the LCD monitor is to use the 5V from the VEDID.  The is pin #14 on the DVI Connector itself.  5V is sent from this via the DVI source (ex the computer) to Pin #14.  This pin is intended to carry the 5V to the LCD panel via the Hot Pink/Red wire in the iMac's Gray LCD cable.  We are already splicing this 3 times so far.  One goes via the Hot Pink/Red Wire to the LCD as noted.  One goes to a 1Kohm Resistor to DVI Pin #16 (The Hot Plug Detect).  The third goes to a 6.8Kohm resistor then to the Yellow (?Wake from sleep wire) of the inverter cable.  By splicing this again we get 5V which can be sent via the White wire of the native PSU to turn the 24V line of the LCD on.  You can splice this anywhere along the line, I did it at the cable that comes to the Yellow wire of the inverter.  I connected an alligator wire to the White Wire of the PSU and hooked it up to the line going to the connection between that line and the 6.8Kohm resistor on the side before it passes through the resistor.  This seems to work beautifully and results in the screen going completely dark during sleep appropriately.  To be honest, I'm kind of blown away at how elegantly this works.

Now if you see 5V for anything else, you will need one of the above methods.  Meaning, use this for the LCD, but if you want to power a drive in the base DO NOT USE THIS SOURCE YOU WILL DAMAGE IT! You will need some type of downconverter, either a standalone or part of a motherboard as mentioned above.

This has gotten me to rethink LED backlighting and I may try adding the touchscreen in some fashion using the existing CCFL LCD.

It is amazing how the components of this decade old, little machine continue to amaze me.  Whether its the mechanical grace of the neck, the remarkable use of convection cooling, or now even a simple/elegant power supply solution for such a limited space, the iMac G4 is truly an inspired design.  To those working on the 17", I have posted information on that inverter which works in a similar fashion.

Thanks for reading!!!