All-In-One 20" iMac G4 "Genuine" TMDS to DVI Mod - Completed (With Guide)

iMac G4 running Lion

As I noted earlier, two newer developments helped with figuring out how to turn on the inverter.  For one, the apple cinema display controller worked with the inverter.  Although this arrangement clearly differed from how the inverter is natively controlled and required an extra wire for sleep function, it allowed me to at least have an idea of the voltages of each wire.  Secondly, using the DVI connector that I discuss in my 17" Guide, I can reliably create a DVI connection for the LCD in 10 minutes.  Before this required cutting soldering, and permanent alteration of the wires and pins.  As such, it wasn't long before the inverter was turning on the backlights.  In fact, the solution was not complicated, I have no idea how I didn't just stumble upon it.  The only special requirements are a 24V line in which there are two solutions I have that both work fine.  I would imagine it is possible to use the native power supply, but I have been told that it can not be "jumped" in standard fashion.


I do want to mention that there are definitely more sophisticated solutions.  In fact, its unlikely that I'll even add dimming and to get the monitor to sleep I'm currently using somewhat of a trick.  There are several people that are using this foundation to do very impressive things and I can not wait to see the results.  What I am attempting to do is create a DIY solution that is both cheap and reliable, but above all is something that can be replicated by someone who has limited technical skill.  Such as the ability to wire up a multi speaker AV receiver and can build a computer from off the shelf components purchased from a store like newegg.  That said, this is not the definitive word, for those with more knowledge and skill, improvements and suggestions will be welcomed.


I will not focus on pinouts in as detailed a manner as I did in my 17" Step by Step Guide.  The guide is essentially the same.  The only differences are in a few pin numbers.  Just use the pinout above as your guide if you need help.  What I will spend more time on is the finalization.  How to stabilize the mod as best as possible and how to put it together, not just as a DVI receptacle in the base but as a sandy bridge updated all in one.  To do this I'll be using the previously mentioned KEEX-6100.

KEEX - 6100 ECX (3.5" board)

This board or several other ECX boards can be obtained from Sliger.com.


Here is their selection of ECX boards


They can help you out with all needed accessory cables as well.  The customer service has been fantastic and I highly recommend Sliger to anyone looking for an ECX board.


This is a fantastic board and whats more is that I can now confirm that this board is indeed "hackintoshable" using a retail/vanilla installation with appropriate boot loader.


I. Power Source
Updated (5/8/12): The original 20" PSU can be used to power the LCD and a computer in the base without use of a second power source.  Detailed below are 3 different methods to power the LCD +/- computer in the base.  The first, using the native PSU and 5V that is provided by your image source via the DVI cable to DVI Pin #14.  Note that this 5V source of power is spliced several times during this mod for various reasons.  The second uses an external power brick that transforms 120VAC to 24VDC then splits to a PICO PSU that accepts the 24V and to supply the 24V to the backlights.  The third uses an external power brick that transforms 120VAC to 12VDC then to a PICO PSU that accepts 12V and a 12V to 24V DC up converter to get the 24V line for the backlights.  All methods work, but the native PSU does not work with this design.  The KEEX 6100 can not fit above the drive with the native PSU.  If you remove the optical drive, you can then lower the mobo and keep the native PSU (This is the preliminary design included in my upcoming "20" iMac G4 Pro Mod").  For this design I went with the third method.


A) The Native 20" PSU

Using the Native PSU alone

Several readers have used the original PSU with success.  Although the original PSU does not fit in this mod, I decided to give it a try.  The original PSU appears to be a 12V only (with one exception) which relies on the motherboard for downconversion to 5V.  The 20" motherboard does two major things with the 5V.  For one, it supplies 5V to the molex cables to power the optical and hard drives.  The second thing is to give 5V back to the PSU in the form of the White Wire(+) and Blue Wire(-) which turns on an up converter or transformer which gives a 24V line (Green Wire and Black/Ground) which powers the monitor.  Initially I was not a fan of this idea because I was under the impression that the White/Blue 5V "jumped" the PSU, so a 5V current was needed from a second PSU in order to turn on the native PSU.  However, the native PSU is on once it is plugged in, so you can use its own current to get the 5V, hook it to a motherboard that needs only 12V and can down convert to 5V (such as the KEEX ECX Boards), or if you don't have any additional needs for 5V except for turning on the power to the LCD's backlights, you can splice the 5V for the incoming DVI.


This method was not used for this mod, but for those interested much more detail is available in this post: 20" iMac G4 - The Native PSU

Briefly, to use its own current a 12V to 5V DC-DC downconverter (<$5) can be used to generate a 5V rail for devices and/or activation of the 24V rail.

12V to 5V DC-DC Downconverter

Also, to activate the 24V rail, you can use the 5V that comes in from your DVI source at Pin #14 as noted.  This is probably the easiest and most effective method.  Just note that this 5V is for turning on the 24V rail and for other purposes described later, do not use this as a 5V rail for devices such as drives as you can overtax and even damage your DVI source.  This method is best rewired in at the end of the mod when everything is hooked up.  Simply take the White wire of the native PSU and connect this to a splice of the incoming wire of DVI Pin #14: The VEDID which has 5V supplied by the incoming video signal.  (Note: Using this method will result in this Pin being split into 4 total wires).  But, do not use this pin to power any peripherals or devices as this may damage not just this mod, but your source (i.e. computer) as well.

Native PSU ONLY - 20" Power Scheme

As the original PSU will not fit in this design which uses the optical drive, the first decision to make is how can we power this in a different, but simple way.  By simple I mean - 1 plug, 1 power brick, 1 on/off switch.  This is actually a bit of a challenge because we not only need to power the LCD, but a Core i series mobo and processor, a 5.25" optical drive, and a HDD or SSD.  This will require something with a decent amount of wattage.  Whats more, the inverter requires 24V DC, the maximum voltage in a standard atx psu is 12V DC.  An ATX psu and all variations (flex, mini etc) simply take up too much room.  A picoATX psu is tiny as it uses an external power brick for AC-DC conversion, but the highest wattage I've seen is 150 - 160 watts.   So really there are 2 choices.  Convert from 120VAC to 24VDC and get a PSU that can handle that or go from 120VAC to 12VDC, get a standard PSU, but then up convert from 12V to 24V.  Again, a third possibility is the native power source, but this doesn't quite fit my design plans, so I will not be pursuing this method.


B) Convert AC Power to 24VDC

24V Power Scheme

AC to 24V DC Brick

I apologize about the crudeness of the above sketch as it is my original notes/design.
To Sum Up:


 An AC to 24V Power Brick is used (in this case the 65W Apple Cinema Dispay's Powerbrick).  I split the 24V DC OUT and Ground.  One part of the split goes to power the inverter, with the 24V connecting to the Red and Blue Inverter wires, and the Ground connecting to the Green and Black Inverter wires.  The other half of the split goes to power a Pico Power Supply Unit.

Variable input Pico PSU

This particular Pico PSU is 65watts and is a "variable" power supply.  This means that it can accept 12 - 24V DC INCOMING and it outputs standard tax voltages.  It has molex and sata power connectors.  The green alligator clips you see in this picture are connected to a rocker switch which I am using to "jump" the pico power supply.


The molex is used to power the LCD which has 3 wires (Purple, Yellow, and Orange) inside the Gray LCD cable which connect to the Yellow Molex wire - the 12V.  Unlike the 17" LCD which requires only 3.3V or 5V, the 20" needs 12V.  The iMac's Gray LCD cable also contains 3 wires which are o be connected to the black molex, the ground.  These are the Grey, Blue, Green wires.


The Purple wire I originally hooked up to 5V Molex, however, it does not seem to play any significant role in this setup and can be left floating.  The Orange wire, likewise, I left floating (it functions as a dimmer, I may try to get brightness working later).  The Yellow is the on/off, which requires a very small voltage.  A 1Kohm resistor works, but I went for an even higher resistor a 6.8Kohm which for testing purposes I hooked up to the red molex (5V), but will eventually hook up to the VEDID.  The reason for hooking up to the VEDID is so the backlights turn off when the led itself is told to sleep.


This method has a few disadvantages however, the 24V backlights are being fed voltage essentially outside of the "control" of the Pico PSU.  As such the rocker switch does not turn off all power going into the computer.  In addition, the 24V power bricks are less common.  The biggest disadvantage however is the available PSU wattage.  The most powerful Pico PSUs I was able to find require 12V DC incoming.  As I plan on making this a Core i/Sandy Bridge all-in-one and 40 or so watts are required for the 20" LCD alone, every watt counts.  So while this method works, I decided to pursue a different approach noted below.


C) Convert AC to 12V then Upconvert to 24V

The largest pico PSU I was able to find was the 160watt PicoXT.  It comes with an admittedly large power brick, but 160 watts should suffice for both the motherboard and the display.  This should eliminate the need for multiple power bricks.  Also, all power flows through this PSU.  In the PSU picture, you can see how the "jump pins" are connected to a rocker switch.  This gives me a hardware, full power off, on the machine.  In addition, the PSU has some useful connectors.  There is a molex (needed for the LCD), a SATA Power (needed for the SSD and DVD drive), and a 4pin CPU connector.  Conveniently, the ECX board this 4pin connector for power.  This particular model also has a convenient external plug, which I will show later in the mod.


As we are starting with 12V DC and the inverter needs 24V, the only way to get the needed voltage is to use an upconverter.  Pictured here is a very reasonably priced 72watt DC-DC converter.  This outputs 24V at 3A which is enough to power the inverter.

DC-DC 12V to 24V Converter

Although it has a somewhat unusual shape, it appears that I will be able to incorporate it into the side of the optical drive cage.  This is simple to use.  Connect the Yellow and Black (12V and Ground) of the molex to the Input and then hook up the 24V and Ground Output to the inverter wires.  The Red and Blue inverter wires connect to the 24V Out and the Green a Black inverter wires connect to the Ground Out.


Otherwise the schematic is the same as above.  The yellow wire remains connected to any resistor of at least 1Kohm (I used 6.8 Kohm) and then to 5V for testing and eventually the VEDID.


Make sure you test this out before proceeding.  The backlight should visibly turn on, it won't be a blinding light, but you should clearly be able tell when it is on or off despite ambient light.


So here is the inverter pinout including the 12V to 24V DC-DC Upconverter, which is the method I currently recommend:

20" iMac G4 Inverter Pinout

And here is the new scheme using this method:

12V to 24V Power Scheme

II. LCD (TMDS to DVI)

iMac G4 20" TMDS to DVI Pinout

DVI Connector

I will show every important step but will not be going into quite as much detail as in my 17" guide.  The principal is exactly the same, but the pinout (which pin plugs where) is different.  Again this method utilizes a special DVI connector that fits into the iMac G4's LCD pins perfectly.


Pictured here is the DVI connector that makes this mod possible.  For details on this connector please see this post: DVI Connector Method.

Female DVI Pin Number from Tom's Hardware

 The TMDS to DVI Pinout shown above has four columns.  The 1st column (left to right) refers to the the cable that plugs into the iMac's LCD at the top of the neck.  As we are not opening the LCD this is not really relevant here.  The second column is the color of the wire that comes out of the iMacs neck.  The ones that say "xxxx to yyyy" are the cables that come from the Black Cable in the neck.  The "single" colors come from the Gray Cable in the neck.  The 3rd column is the function and the 4th/rightmost column is the DVI pin number.  It is this column that refers to the location/pin on the FEMALE DVI Connector.

Remember, this pinout refers to the FEMALE connector only.  In reference to our connector the pin numbers are shown to the left.  The iMac's LCD is Digital Only.  DVI can have both digital and analog areas.  This connector is digital only.  There is a horizontal slit where the analog pins would have been.  I refer to this as the "Analog Area" and it is for orientation purposes only.


Although we know the pin number from the front, this is a right angle connector.  So we have to "trace" the pins and identify them on the bottom of the connector.

The pins make a 90 degree turn

The Most Important View - The Bottom Pins

Looking from the Bottom, The Top Row ends up at the back, the Middle Row in the middle, and the Bottom Row closest to the front.  This is where the female pins of the iMac's neck cables plug in and thus the most important view.  Using this view and columns 2 and 4 in the TMDS to DVI pinout you have all you need to complete this.  Take the color from column 2 and plug it into the numbered pin pictured above identified by column 4.



A) The LCD cables


Left of the connector you can see the iMacs LCD cable.  Originally this comes in a connector that plugs into the motherboard.  Using a flat head screwdriver and safety pin, you must free the individuals pins from the connector until they are all free as pictured.  DO NOT REMOVE OR DAMAGE THE PINS AT THE END OF THE WIRES.  Take your time and be gentile.

For the iMacs LCD cable you must first remove the metal casing using a flat head screwdriver or x-acto knife.

- First pry open the top

- Then the side

- And then the metal cover should bend back and snap off

When the black is fully exposed you will again see little plastic tabs on the side.  Using a safety pin lift these tabs and push them down (its ok if they come off entirely).  You want to see the exposed metal from the pins where the tabs used to be.  Do this for all the tabs on both sides of the cable.

When all tabs are done, VERY GENTLY pull the individual wires and pins free.  This should not require any force, the pin should easily slide out.

If there is any resistance, then you may need to again use your safety pin to press down on the pin in the area where the tab used to be in order to help free it from the black connector.  Usually once you push it down a little the pin will become "unstuck" and then will be able to be removed without difficulty.


Although not required, I have found it helpful to cut the tape that holds the Gray and Black cables together allowing the two cable to be manipulated individually.  Once both cables with its pins intact are free you can begin hooking them up to the DVI connector.
 
B) The DVI Connector - Black Cable





 LOCATE PINS 1, 2, and 3 on the DVI.
   - Closest Row to the back of the connector
   - Furthest from the Analog Area
   - Find the iMacs Black Cable and isolate the Brown Wire
   - Take the Green Wire in the Brown Wire and Press it into PIN#1
   - Take the Red Wire in the Brown Wire and Press it into PIN#2
   - Take the Black Wire/Shield in the Brown Wire and Press it into PIN#3












LOCATE PINS 9, 10, and 11 on the DVI.
 - Middle Row: Directly in front of the Brown Wires Just Placed

 - Furthest from the Analog Area

 - Find the iMacs Black Cable and isolate the Blue Wire

 - Take the Green Wire in the Blue Wire and Press it into PIN#9

 - Take the Red Wire in the Blue Wire and Press it into PIN#10

 - Take the Black Wire/Shield in the Blue Wire and Press it into PIN#11

LOCATE PINS 17, 18, and 19 on the DVI.

 - Closest Row to front: Directly in front of the Blue Wires Just Placed

 - Furthest from the Analog Area

 - Find the iMacs Black Cable and isolate the Green Wire

 - Take the Green Wire in the Green Wire and Press it into PIN#17

 - Take the Red Wire in the Green Wire and Press it into PIN#18

 - Take the Black Wire/Shield in the Green Wire and Press into PIN#19 

LOCATE PINS 22, 23, and 24 on the DVI.

 - Closest Row to front: Same row as the Green Wires Just Placed, however at the other end.

-  Closest to the Analog Area

 - Find the iMacs Black Cable and isolate the Red Wire

 - Take the Green Wire in the Red Wire and Press it into PIN#24

 - Take the Red Wire in the Red Wire and Press it into PIN#23

 - Take the Black Wire/Shield in the Red Wire and Press into PIN#22

 - ***Notice that the wires are placed differently here, from left to right it goes Black, Red, Green, which is the reverse of the previous placement.  One way to confirm is to make sure the small Green wire is always on the outside, the red wire in the middle, and the shield/black wire should be the "innermost" wire.

Here is a summary picture showing where each wire should go:

For now focus only on the black LCD cable.

As Shown, The Black cable gives off 4 wires:

BROWN

BLUE

GREEN

RED

Each of these is composed of 3 subwires, a Negative, Positive and shield.  These are the small Green, Red, and Black wires respectively.

Please confirm that what you have matches this illustration.

C) The DVI Connector - The Gray Cable

There are a total of 9 wires in the Gray Cable, only 3 of these hook directly up to the DVI Connector.  The other 6 are used for powering the LCD (3 cables for Grounds and 3 cables go to 12V)

So 3 wires go to 12V - This is the Yellow Molex Wire

-  For those familiar with the 17" mod please note that this represents a substantial voltage change.  (3.3V or 5V to 12V)

-  I am using alligator clips for now but will replace this with actual wire later.

-  The 12V wires are the PURPLE, ORANGE and YELLOW

3 wires will go to the ground wire - This is the Black Molex Wire

- The Ground Wires are the GRAY, BLUE, and GREEN

12V and GroundWires

3 wires remain, these will hook up to the DVI Connector

-  2 wires (WHITE and BLACK) are straight forward.  Go ahead and hook these up.  The Black wire's pin pushes into DVI#6 and The White wire's pin pushes into DVI#7.  The final pin in this row #8 is left unconnected.  

-  1 wire (RED - has somewhat of a "hot pink" hue) is more complex as its needed for 2 purposes.  One is to plug into pin #14 - but a modification must be made first.

D) The DVI Connector - Create our own cable.

The reasoning for this is explained in my 17" Guide, so I will not get into it here.  Suffice to say that a small amount of voltage is required to feed back from the LCD to the DVI source.  The iMac does not provide this (it was an all-in-one, so was not designed to detect when its own monitor was plugged in).  We will work around this by feeding the DVI connector its own voltage right back to itself.  This is called the Hot Plug Detect.  In addition an extra DVI to ground is needed.

What is needed? 4 wires of a similar gauge to what is found in the iMac's Gray LCD cable.  A 24 - 28 Gauge will probably suffice.  However, 3 of these wires should include female pins.  The easiest source of such cables is an extra iMac Neck (of any size).   As they include the correct size of pin, this would be the easiest.  However, alternatives include LVDS wires, as well as unused wires in the iMac itself such as the fan wires, the internal speaker wires etc.  You do not need long wires at all.  You could probably get by with each being about 6 - 10cm or so.

The most important thing is to make sure things are well secured and to do this, you really need the proper pins.  While I used wires from an extra iMac neck, I just realized for those without an extra neck, there is a great source of extra pins and even wires staring right at you:


     The iMac's Gray LCD cable's 12V (ORANGE, YELLOW, and PURPLE) and GROUND (BLUE, GRAY, and GREEN) wires.  Unlike the very difficult to work with wires in the black cable, these are much easier to strip and manipulate.  What's more is that these are not signaling wires, so a less than perfect hook-up will not cause any distortion of your image.  These wires are not plugging into the DVI connector so the pins are superfluous.


I still recommend using the wires from an extra neck if you have it as once a wire is cut there is no going back, but this is certainly a viable alternative.


So either:
A) Cut 3 or 4 wires from an extra iMac G4 neck (about same gauge as wire in Gray iMac LCD cable).  3 of these wires should have the female pins that connect to the DVI Connector (about 10cm).  And one other similar gauge wire (can be shorter), with a male pin if possible, but definitely not a necessity.  I will refer to this last wire as the "Extra" wire.

3 Cables from extra iMac neck Gray cable (Green, Orange, Yellow)
and 1 White LVDS wire with a male pin on its end

OR



B) Peel back the Gray LCD cable's Plastic and Shielding about 16cm.  Isolate the Ground Wires: BLUE, GREEN, and GRAY. (You can use the 12V wires as well, but I would feel safer cutting the grounds).  Cut these three wires at about 10 - 12cm).  Make sure you leave enough wire remaining so that the remaining ends can be easily stripped.


*Note these pics reflect an extra damaged iMac cable I had.  I had this idea too late for this mod, but I will use this method for my 17" 1/1.25 Ghz Guide.

Plastic and Shielding Peeled Back

Take the now cut ends of the BLUE, GREEN, and GRAY wires in the Gray LCD cable and strip the last few centimeters of each of these wires so that each now has exposed wire at the end.  Twist these 3 wires together.  You can now hook this up to an alligator wire or a different wire and hook it back up to the black Molex/ground.


The 4th or "Extra" wire can really come from anywhere, if you do not have any other small gauge wires, you could cut 1/3 of the non-pin ends of one of the wires you just cut.  Or just take one of the fan wires or internal speaker wires etc. that are not being used in the iMac's casing.


1.  The First wire - I used a GREEN Wire, with female pin, the Ground
- Strip the non pin end of this wire
-  Push the female pin of this wire into DVI Pin #15
-  Take the stripped end of the wire and wrap it with the other ground wires from the iMac's gray LCD cable.  Either wrap it around the pins or twist it into the the stripped wires the you just cut.  So this wire should join with the BLUE, GRAY, and GREEN wires from the Gray LCD Cable and connect to the Molex's ground/Black wire.

2.  The Second wire - I used an ORANGE Wire, with female pin, the VEDID
- Strip a large portion off the non pin end of the wire (a good 4cm)
-  Take your "Extra" wire - Mine is white - and strip one end.  If it has a pin strip the non-pin end.  If it has no pins, strip both ends.  

Second wire [Orange - Bottom Right] with "Extra" Wire
[White - Bottom Left] coming off and remaining stripped wire seen on top

- Wrap the stripped end of the "Extra" Wire around the Second wire's strip.  But do this at the very beginning of the strip. close to were the plastic covering resumes.  So your wire should look like above with a large part of the second wire's exposed wire still coming out.


3.  Take a 1 Kohm resistor and connect it to the remaining exposed wire from the second wire

With Resistor Added

4.  Take your third wire - I used a YELLOW wire and strip the non-pin end.  Wrap this wire around the other end of the 1 Kohm Resistor

5.  Secure the resistor with electrical tape +/- solder

6.  Connect the 3 ends of your newly constructed cable
-  The second wire (ORANGE) has a female pin that should be pushed into DVI PIN#14
-  The third wire (YELLOW) has a female pin that should be pushed into DVI PIN #16

-  The "Extra" wire (WHITE) has either a male pin or stripped end.  This should connect to or wrap around the Red (Hot Pink) Wire's Pin from the iMac's Gray LCD Cable.  Leave this connection exposed or at least accessible, as we will eventually add something to it.

Hot Pink/Red Wire Interface

- What we've done is create a cable that takes the voltage from Pin #14 and splits.  One split continues unaltered (Orange Cable to White Cable) and connects to the Red/Hot Pink wire as it was intended.  However, the other split runs the voltage from Pin #14 through a resistor and then gives the reduced voltage back to Pin #16 (Yellow Cable) - The Hot Plug Detect.

7.  Controlling the Inverter.  The final thing I recommend doing is to connect the Yellow Wire of the Inverter (the on/off) NOTE: I DO NOT MEAN THE  YELLOW CABLE I USED ABOVE.  to the Hot Pink Wire, the VEDID.  Leave the Yellow wire hooked up to the "at least 1 Kohm resistor" (I used a 6.8Kohm, but tested it with a 1Kohm which worked, though 6.8Kohm better approximates the original signal, but use an extra wire - I used a green wire, to connect to the Hot Pink/Red Wire Interface above.  I simply stripped the wire and wrapped it around.  This is optional, but whats nice about this is that the backlights will turn on and off with the signal it gets from a computer, instead of having to turn the backlights on and off seperately.


8. Test your signal.  Hook the DVI up to a working computer capable of displaying graphical images (no just a boot screen).  Look at the picture closely, look for color distortion or red/green flickering dots.  Color distortion may indicate something hooked up wrong, dots flickering indicate crosstalk.  Remember TMDS uses very slight variations in voltage between the wires to determine what gets output.  If there is a nearby wire with relatively high voltage it may "communicate" with a nearby pin.  Make sure the pins haven't bent  and are spaced apart and consider even adding tiny pieces of electrical tape around pins.  (Especially the small Red/Green/Shield Pins that are near pins the carry voltage.  Make sure your image is pristine before continuing.


9. Replace the Alligator Wires.  Assuming everything works, its time to use extra wire (18 to 24 gauge) to replace the alligator wires (technically you could cut the alligator wires themselves, but this would waste them).  I recommend soldering stripping the wires, wrapping the wires around the pins, soldering them and using either heatshrink and a heat gun or electrical tape to secure them.


10. Secure your wire.  Solder only if you are an expert, its very easy to solder nearby pins together.  Instead I used a great insulator - hot glue.  After using some electrical tape I coated the wires and pins in the back of the connector in hot glue using a hot glue gun.  This is secure and truly works as a great insulator.  However its hard to get glue in between everything (thats why I advise ensuring no crosstalk before this).  After that I wrapped the wire in aluminum tape.  I used a male DVI to female HDMI adapter and a short HDMI wire to connect to my computer.

The completed wire

Finalized with Important Wires Labeled

Above you can see that 3 wires have to be allowed to emerge from the DVI cable itself.  These are the wires connecting the 3 12V to the Yellow Molex (White Wire), wires connecting the 3 +1 Grounds to the Black Molex (Black Wire #1), Yellow Inverter cable on/off to resistor to the Hot Pink/Red wire interface (Green Wire).

Also the inverter cable can be seen next to it with a Yellow cable emerging from the Blue and Red Inverter Wires and going to the 24V up converter and a Black cable emerging from the Green and Black Inverter Wires and going to the 24V Ground up converter.

E) Optional iMac G4 wires (WiFi Antenna, LED Power Indicator, Microphone)

Soldered Cable

1.  WiFi antenna: There are a few extras wires in the base and from the neck that can be used in this mod.  In side the base you will see two antenna wires emerge from a hole in the base.  These wires go to an antenna that wraps around between the faraday cage and the white plastic of the dome.  The faraday cage is built to suppress electromagnetic signals, so it impedes Wifi.  I used a Broadcom PCI express wifi used in MacBooks for Lion compatibility.  This has antenna holes that connect to an antenna (You may need to sacrifice a third party antenna to get the connector).  I then soldered the inner wire and shield to the iMacs wire.

Secured with Electrical Tape

2.  The LED.  These are two small wires (red and green) that emerge from the neck with the microphone wires.  If you have some motherboard connectors you can solder these wires to them and then connect to the power LED on your motherboard.

Hooked up to Motherboard Power LED.
Also seen are the antenna hooked up to the Broadcom Wifi

Tip, Ring, Sleeve

3. Microphone.  The microphone has 3 wires a thick black, a thin black, and a red wire.  This has a TRS (Tip, Ring, Sleeve) arrangement.  For more details see my iSight Post.  Take a 3.5mm Audio Cable and cut it - three wires will be seen.  The colors may vary, but you need the Ring (Red in my wire) and Sleeve (non-covered in my wire).  Connect the Ring to Red wire of the iMac mic and the Shield to the Thin Black wire of the iMac mic.  The Thick Black wire of the iMac is not connected.  Nor is the tip (the white wire in mine) of the 3.5mm cable.  Also make sure the white wire does not touch anything.  You can hook the 3.5mm jack up to any mic source.  Since my onboard audio is not lion compatible, I plugged this into Turtle Beach's USB audio adapter's mic then into a USB port.
In the audio out port I plugged the 3.5mm audio extender as this will be wired to the back of the iMac (to the rear ports).  Speakers will plug in here.

Testing the LED and Microphone with
Alligator Wires

Turtle Bay USB Audio

F) The Computer/The Base

Now you can connect your power to any molex source and your DVI to any compatible video source,  Your internal designs may vary but this is what I used.

1.The Components:

Motherboard: Quanmax KEEX - 6100 Sandy Bridge ECX Motherboard
CPU: Core i5 Mobile 2520M
RAM: 1 x 4GB 1333 DDR SO-DIMM (Can support up to 8GB)
Power: 160-XT Pico Power Supply with 4 pin power plug and external Power Brick (+ up converter)
DVD: Lite-On 24X DVD Burner with Lightscribe support
Fan/Heatsink: Dynatron Socket G l2 Mobile Cooler
Compact Flash: (Optional - Mac OS will not natively recognize this in AHCI mode) - I installed
                          Windows 8 DP on this.  Transcend 32GB CF Card
SSD: OCZ 64GB SATA II 2.5"SSD
Audio: Turtle Beach Amigo II USB Sound Card
PCI Express Wifi: Broadcom BCM94322MC PCI express Wifi
Extras: 16GB USB stick for Lion installation
            Griffin iFire Adapter for speakers with PCI express to AC adapter
            Sheets of Styrene
            iMac G4's DVD and HDD cradle
            Hard Plastic Spacers
            Computer Screws
            Rocker Switch
            Computer Power Momentary Switch
            Computer Pins and extra Wires
            2.5" SSD Rubber Case
            Velcro
            Hot Glue Gun
            Modeling Clay
            Gorilla Glue
            Double Sided Mounting Tape
            Aluminum and Electrical Tape
            Dremel
            Motherboard Pins to 2 USB ports x 2
            Cable Ties
            Bluetooth USB Dongle (Was an extra, not exactly sure of make)
            Wired Keyboard and Mouse
            Male DVI to Female HDMI adapter
            Short 1 foot HDMI cable
            (If your PSU does not have a 4pin power then you need a Molex to 4pin adapter, this one did)
            4pin PSU power female to male extender
            SATA cables x 2
            SATA power splitter (PSU had only one SATA)
            3.5mm Audio Jack Extender
            Ethernet Extender (I used an ethernet splitter and dremeled off one side).

Software: Purchased copy of Mac OS Lion, Tonymac's Unibeast, Realtek or Intel's Gigabit Ethernet Kext
Note: I installed Lion externally and I recommend doing this to ensure compatibility and to ensure everything works before placing everything inside.

2. Setup

Wire Management

You will notice that I opted against a case fan.  The fan actually presses into the board when using the native adapter (This should give you a sense of just home little room there is above the drive).  Initially I had a setup with a smaller 80mm (native is 92mm) fan sitting directly above the board.  I tried multiple setups with both an active and passive cpu fan (Cooljag makes a passive Socket G Heatsink) and the case fan blowing both in and out.  Although blowing in kept the overall board cooler, it only helped with the passive heatsink (active heatsink alone was better than this arrangement with passive heatsink).  Blowing out made only a marginal difference unless the fan was ramped way up (then it was very loud).  The best compromise I found was using smart fan settings in bios to ramp CPU fan up when temps exceed 65C on the CPU.  This allows the computer to be whisper quiet doing almost any every day task, while not allowing CPU temps to go too far over 70C under high load.  Note that this requires compromise, the motherboard is essentially in its own compartment with its fan placed directly under, only a few cms from the exhaust, the heat generating component of the PSU is external, and I did not go for a quad core mobile chip.

Alternative Design: I debated for a while if I should do this or to loose the internal optical drive and use a 92mm case fan as well (as a second internal fan vs heat pipes or small liquid cooler), with a more powerful cpu heatsink and cooler and the native psu.  This would allow me to place the board somewhat lower to fit the native psu and properly cool it.   Thus, I could use a more powerful mobile processor core i7 quad core.  In the end I decided I did not need bleeding edge power and I opted for a closer to original iMac G4 experience with quiet operation and onboard optical drive.  Though I am tempted to try this in a future build.

You may ask why I didn't use a male version of this DVI interface, the answer is that I couldn't find one.  This interface is so by far the best way to go, not only in terms of ease, but in terms of stability.  Almost all my mods where I solder the Black LCD cable to a DVI or HDMI result in some pixelation or distortion and I have heard the same from readers as well.  If a solder point changes resistance even a little, you will have image problems.  So I added an HDMI adapter and short HDMI cable.  I secured these to the top of the dome.  I used aluminum tape to position and hot glue to secure.  Using cable ties I made the wires as short as possible using the sides of the top of the dome (one of the only areas of free space).

Lay it out as its supposed to work

Turn it on with everything hooked up as it should be one last time.  (Nothing is more frustrating than having to disassemble everything to fix one small thing.  Note: There are two different ethernet ports with two different chipsets.  Use only one, (both have available kexts - choose which one you want and install that next).  I used the Intel Gigabit and then disabled the other LAN in the bios.  I hooked up the ethernet extender to this one.

I also modified the drive cradle, cutting off the pieces on top of the optical drive that were meant to cradle the HDD.

3. Installation

I used a hard rubber spacer and dremeled screw holes into 4 pieces.  I used a thick piece of styrene to use as a motherboard tray.  I personally like styrene as its firm, non-conductive, but is easy to cut.

Spacers

Screw in first to determine placement

 The spacers were glued into the proper positions (screw holes) on a sheet of styrene that was slightly longer than the ECX motherboard itself.  This is important as you do not want the motherboard to lay flat, some ventilation must exist for the underside of the board (contains RAM and Compact Flash).  Then I screwed the motherboard onto its styrene tray via the spacers.

Fit testing

The image on the right is a fit test.  I used aluminum tape to secure the board and adhesive to make sure the optical drives cradle came into contact with the styrene.  Notice that the board is right of center.  This is done to allow the bulky cable plugs, USB and HDMI to fit.  Wires also come down from both sides depending on where I need it to go.

When I was secure in my position, I glued the styrene onto of the optical cradle on all put the leading edge.  As you can see there is a metal tray that I left in place.  This leading edge allows me to slide this edge of the styrene with motherboard on top of this tray.  The other sides are glued to the drive cradle.  Which can then be screwed into its native holes.  Thus, the motherboard is double supported.

Make sure all cables are to the sides and that no wiring goes over or impedes the fan on the motherboard in any way.

With the DVD installed you can see how little room is left.  As a matter of face to two areas on each side of the DVD are all we have left for our power source and up converter.

The placed the PICO PSU to one side and the up converter on the other side.  To give myself more room I did cut down the "wings" of the up converter with a dremel, though this is likely not necessary.

Below the drive there is just enough room for the 2.5" drive to squeeze.  I put this in a rubber internal 2.5" HDD case and with velcro secured it to the bottom of the drive right above the access panel in the bottom of the iMac.  This may not be the most elegant solution, but it works great.  As most of the boards over specs I'm unlikely to change, the SDD is something I could see myself swapping out.  So unscrew the bottom panel as if changing the RAM or adding an airport card in the original iMac G4. Pull off the SSD in its case enjoy the satisfying tear of velcro, swap it out and put the new one back and you are done.

4.  Power Button and Ports

One way to do the power button is to secure your momentary switch right behind the original power button.  This seemed to work great , but I unfortunately pushed in too far one time and dislodged the power button.  So I swapped it out with a small threaded black power button for now.  I am awaiting delivery of a smaller silver power button of the same size.  Although the native switch is more elegant, I do not want to worry about how hard I press the button.  The threaded power switches are bolted in and therefore more stable.

How far you want to go with ports is up to you.  The easiest solution is to let the wires poke out the back as I did initially.  Another way that I did it initially was to use the ports I created as part of my Core 2 Duo ECX mod

Using modeling clay to secure the USB and Ethernet ports.  Some dremel modification was needed.

 I removed the unnecessary wires and replaced them with the current ones, this time using hot glue.  However, I was having some instability with the ports.  Occasionally pushing the panel in.

Ultimately, I decided to secure the extenders from the inside.  So that what ever I put over them would just be a "covering".

 I designed white styrene "caps" for these ports.  But, I am holding off for now as I have actually invested in Makerbot's replicator (3D printer).  As a modder, I can't tell you how many times I wish I had "a little piece shaped like X" - hopefully "with a learning curve" I'll be able to figure this out.  Once it comes my first project with it will be port covers.

Also, I had initially intended to internalize (even took it apart) my ifire, however I felt is was too much of a power drain.  So, the ifire is external.  As I don't have a firewire port, I used a firewire to AC adapter.  I made my own, but apple did sell one, and they are easily obtainable.  You do not have to use the apple pro speakers, I just have always liked the way they looked.  If you don't have an ifire and are interested in this speakers please see my extensive post on my experience and advice with these speakers called Proprietarily Ridiculous - The Apple Pro Speakers.

Completed Mod

So thats the 20".  As you can see this is not the only way to do this.  But as with any mod dealing with a tight space you have to make compromises.  I honestly believe this is the best balance I can achieve at this time.  As technology keeps improving and things continue to shrink, this will likely change.

I have been using this extensively over the past several weeks and I am thrilled.  Its fast and powerful and I have yet to hear the fan have to crank into high gear.  As I mentioned I did add a Windows 8 DP dual boot, which has also been fun to play around with.

This mod is a culmination of years of hard work for me.  This is what I had hopped to build when I started but quickly found that it was impossible.  With every successive attempt I felt I came closer and closer and have now completed what (as little as 6 months) did not think was possible.  I am also happy that I am able to share it with others who also love the design of the iMac G4.  One thing I did not like about my other 20" mods is that I didn't feel they could be easily reproduced, I can confidently say that using the DVI connector I discussed this mod can be done by someone with minimal modding experience.  I appreciate all the feedback and as always am happy to answer any questions.

I would also like to give my appreciation to other modders pgee, JeanLun, and bluegray without whom I would have been stuck at various points along the way.

Thanks for reading!!