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!!