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iMac iSight Model Power Supply Unleashed

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Introduction

With the growing interest in iMac G5 builds appearing on this forum (which is great to see!) I thought I would take the time to post some info which may prove helpful for upcoming mods. It comes as a result of some research and testing which in all honesty I wish I could've accomplished sooner. Myself, I've built three G5 projects, only one of which (a non-iSight A1076 model) utilized the original Apple Power Supply. This thread will focus primarily on the iSight models of iMac PSU.

My three iMac G5 projects are linked below for reference.

http://www.tonymacx86.com/imac-mods/148974-ersterhernds-imac-g5-20-inch-a1076-project.html
http://www.tonymacx86.com/imac-mods/128390-ersterhernds-imac-g5-isight-20-a1145-project.html
http://www.tonymacx86.com/imac-mods/124456-ersterhernds-imac-g5-isight-17-project.html


The two iSight builds I completed did not use the original iMac PSU. There was three reasons for this...

1. I had no idea of the PSU pinouts or operating function.
2. They were only in fair to poor working condition.
3. I was fearful of connecting an new Intel NUC to an old PSU.


Reasons aside, there are many old iMacs still around with Power Supplies in excellent condition. Furthermore, there are new and refurbished PSU's available online. The iMac mods completed on this forum so far produce only a small fraction of the power draw and heat that the original G5 computers did, so the life expectancy of a decent original PSU is likely dramatically increased. That, combined with the efficiency, cost-effectiveness and 'coolness factor' of re-using original parts makes the stock PSU option very attractive.

One problem exists though; other than an occasional dated internet forum post, there is little if any information about the iSight PSU's available anywhere. After embarking on some research and testing, this thread will hopefully answer most questions about these obscure pieces of hardware.


The Hardware

The iSight model of PSU exists in many variants & part numbers, but primarily in one of two forms.

1. The 17-inch iSight iMac G5 PSU

This version consists of an AC to DC 185W PSU and a DC-DC converter which is attached by a short 5-pin connector cable. The 120V or 240V comes in via the iMac power cord and AC Filter, then is distributed in 3.3V, 5V and 12V DC and Ground through a 12-pin (2x6) & SATA connection cable to the iMac Logic Board.


The 185W PSU

screenshot_50.png



The DC-DC Converter

screenshot_51.png



The 2x6 Pin & SATA Connector Cable

8gODtW.jpg




2. The 20-inch iSight iMac G5 PSU

This version consists of the same AC to DC 185W PSU but with a DC-DC converter specific to the 20-inch model only. The same 5-pin connector is used to join the PSU to a second piece. In this case, the DC-DC converter is combined with an LCD inverter to supply power for the six backlights in the 20" LCD. The backlighting is 24V, which is upconverted from 12V by this combination DC-DC/LCD Inverter. There is a 2x7 14-pin connector hard-wired to this part, and also there are four connections for the LCD Inverter Cables to plug into. It is a MUCH different part than the simpler DC-DC converter of the 17" iMac.


The 185W PSU (same or variant of the 17-inch version)

screenshot_50.png



The combination DC-DC Converter & LCD Inverter
(Note the hard-wired 2x7 14-pin connector cable)

0psv.jpg




The Pinouts

For purposes of demonstration, I will label the pin numbers in the following format. This may be different than displayed elsewhere. I will include both the 17 and 20 inch iSight pinouts in a single diagram. The connector as shown below is from a 17" iMac iSight. The 20" version contains 2 extra pins which are simply drawn onto the photo.


DDy7EP.png



Pin Number, Name and Confirmed Input/Output

1. PS3V3_RUN = 3.3V
2. PS5V_RUN = 5.0V
3. PS_GND = Ground
4. PS12V_RUN = 12.0V
5. PS_GND = Ground
6. POWER_GOOD = Not Used
6A. LCD_PWM = TO Brightness Control 0.8-3.3V (20-inch only)

7. PS3V3_ALL = 3.3V
8. PS_GND = Ground
9. PS5V_ALL = 5.0V
10. PS12V_ALL = 12.0V
11. PS12V_ALL = 12.0V
12. SYS_POWERUP_L_BUF = TO Ground/3.3V to Switch On/Off pins 1-6A
12A. INV_CPU_HI = Not Used (20-inch only)


The Function

The pins on both the 17" and 20" iSight G5 models are divided into two separate banks. Pins 1 through 6A (Bank One) are 'run time' pins that can be turned either on or off via pin 12. Pins 7 through 12A (Bank Two) are 'always on' pins that are active at any time the AC is plugged in. When pin 12 is connected to a 3.3V source (ideally pin 7) then pins 1 through 6A are turned off. When pin 12 is connected to ground (ideally pin 8) then pins 1 thru 6A become live.


Pin 12 Controls the on/off switching of Pin Bank One.

4zdOgQ.png




For iMac Mods, this two-bank layout with one switchable and one 'always on' bank of power provides a huge advantage. It allows the system to use only the native power supply, with the ability to turn the power on or off very simply, without the use of a second power supply or microcontroller circuit. Additionally, the feature of the LCD_PWM pin 6A on the 20-inch model gives single-wire control of the screen brightness. All 24V upconversion for the backlights is handled by the DC-DC converter.


The Practical Application

There are likely many ways to put this Power Supply into effective use. Here is just one method that I've successfully tested that will work in an iMac Mod. It uses a simple relay to switch the iMac power supply Bank One pins on and off. The relay is can be purchased at this link.

I will reference the use of the Intel NUC for purposes of this demonstration. The i5 Haswell D54250WYK operates at 12V which could be supplied by the 'always on' pins 10 or 11 of the iMac PSU. Even using older 19V versions of the NUC (pre-Haswell) the 12V iMac supply could be easily brought up to 19V using a DC step-up converter. The Intel NUC is currently the best candidate for success in iMac G5 mods.


Schematic Diagram for utilizing the Intel NUC with the iMac iSight Power Supply
(Connection to 17" model shown, 20 inch adds two pins 6A and 12A on right end of connector)

schematic1.png




Photo of the relay working perfectly to switch the Apple iMac PSU Pins 1 thru 6A on and off.

RvvgM8.jpg




Photo of the 'Control' side of the Relay (in a real application would be wired to the Intel NUC)
The White wire will go to a 5V source (USB pin or Front Panel Pin on Intel NUC)
The Purple wires go to a ground (USB or Front Panel GND Pin on Intel NUC)

kUzXVK.jpg




Photo of the 'Load' side of the Relay wired to the iMac PSU
The Orange wire goes to Pin 7 of the iMac PSU (3.3V ALL)
The Center Green wire goes to Pin 12 of the iMac PSU (SYS_POWERUP_L_BUF)
The Left Green wire goes to Pin 8 of the iMac PSU (PS_GND)

gAdvzI.jpg




The sequence of operation would be as follows:

1. Plugged into 'always on' Pin Bank Two 12V pin 10, the Intel NUC sits ready in standby mode.
Fans, LCD, Backlights etc are all OFF as they are plugged into Pin Bank One which is off (pin 12 = 3.3V).

2. iMac Power Button pressed. NUC starts and sends 5V to Relay via USB 5V or Front Panel Pin 9.
Relay becomes energized, switches the load circuit side from 3V to GND on the iMac PSU Pin Bank One.
Pin 12 goes to ground (was 3.3V when system off) and Pin Bank One becomes live.

3. Fans, Backlights, LCD and all other runtime components become active via Pin Bank One.

4. At shutdown, the reverse sequence occurs, leaving Pin Bank One 'off' and only the NUC in standby.


A demonstration video to illustrate this sequence. It clearly shows the iMac PSU ability to maintain an 'always on' and 'switchable' set of power simultaneously via Pin 12 connected to a Relay.

1. The 12V 'always on' fan resembles the Intel NUC.
2. The white 5V wire resembles the power supplied from Front Panel Pin 9 on the NUC
3. The switchable on/off fan resembles all other components in the system (LCD, Fans etc)


Here is a YouTube Video of the working model...




I hope this post helps to illustrate the easily usable functionality of the iSight native PSU. I'd like to thank YouTube user 3beltwesty for his efforts in preparing 5 videos during his research of this iMac power supply. His informative tutorial gave me a lot of information that I wish I'd had much sooner. I will likely be pulling one of my G5 iSight builds apart to give this a full-on attempt. Will post that progress if or when it occurs.


Ersterhernd
 
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Hey ersterhernd,

Currently attempting a G5 mod of my own, and I'm up to testing the LCD.

The current PSU I have I believe is dead, so I'm attempting instead to hook up the DC-DC/inverter to an HD-Plex 250W power supply instead. I've already hooked up the DVI connector to the LCD, and attached the 3.3V, 12V, and ground lines to the appropriate spots on the HD-Plex.

From some source online, I found that the 5 wires coming out of the PSU and into the DC-DC/inverter correspond to 12V, ground, and PFW (gray, black, brown). I have the PFW attached to 5V, and everything else attached to their respective locations as well on the HD-Plex.

When I short the HD-Plex to turn it on, however, the LCD is unresponsive, but the PSU is clearly on. Testing for voltages on pins 1-6a (the always on half) of the 14pin connector from the DC-DC/inverter gives nothing.

Before I blame a faulty inverter, is there anything that I seem to be doing wrong/should further test?

Any help I could get would be great!
 
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Hi perpension, Apple designed the two components to work in concert with each other. There must be some technical reason why PSU isnt starting the DC/DC converter but I couldnt venture as to why. The original parts contain the proper mounting holes that mate up with the inner holes on the iMac, and these PSU's are a plentiful on eBay now. I would simply order a working replacement to preserve the originality of the project.

When I did my iSight builds, I didn't know about the inner workings of the Apple parts so used my own variant to get the power and inverter going. That said, If I knew then what I know now, I'd have used Apple original parts.

Good luck with your build and post pics as you go...


Cheers!
 
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Hi Ersterhernd,

I'm planning to build a gaming pc in an old imac I have lying around.
I'm going to use a thin mini-itx motherboard which uses a laptop adaptor as psu, just like the intel nuc.

Is it possible to use the original power supply with such a board?

Also I am planning to use a discrete gpu, and power it with a HDPlex DC-ATX and and extra external psu.

Would it be possible enable the hdplex only once the imac psu has booted?

Anyhow, thanks for the immense amount of info you've put up on the forum.
I wouldn't even have thought of the idea if it wasn't for your projects ;)
 
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Hi Molokotof, before you spend any money on components, I would determine if your configuration will fit. The iMac size is deceptive, you actually have much less working space than appears from the outside due to the metal frame and internal hinge point for the base. I just barely fit the NUC into it, depth clearance was extremely tight.

The original power supply will save you a lot of space, but its effectiveness and stability will only be confirmed with testing. I wish I could answer more definitively, but I haven't yet actually accomplished it with actual hardware.

Post your results if you give this a try.


Cheers!
 
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Hi Ersterhernd, i already got a used motherboard on the cheap, in case it doesn't fit I could still stick it into another pc case...

It's also sub 25mm thick (all i/o included), as per thin mini-itx spec.
The motherboard is actually spec'd for All-In-One pc's, and it actually had brightness and backlight inverter pinouts.

So i'll have to look into that aswell.

Anyway, thanks for the reply and i'll keep you updated ;)
 
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I have a 17" A1208 EMC 2114 white isight iMac that I am attempting to fix for a charity. The iMac is completely dead, doesn't power up, none of the diagnostic lights on the board light up. As far as I can see, none of the capacitors on the power supply are puffy as I hoped they might be, so I would guessing if replacing any or all with new ones will work. Anyone know what the typical causes of death of this model are? A search engine search didn't prove very helpful. I have probably taken on more I can chew with my limited knowledge. I can solder neatly, have bought a multimeter but I imagine learning to use it would take some time and any readings fairly meaningless without a schematic with values on it. Many thanks for any thoughts.
 
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I have a 17" A1208 EMC 2114 white isight iMac that I am attempting to fix for a charity. The iMac is completely dead, doesn't power up, none of the diagnostic lights on the board light up. As far as I can see, none of the capacitors on the power supply are puffy as I hoped they might be, so I would guessing if replacing any or all with new ones will work. Anyone know what the typical causes of death of this model are? A search engine search didn't prove very helpful. I have probably taken on more I can chew with my limited knowledge. I can solder neatly, have bought a multimeter but I imagine learning to use it would take some time and any readings fairly meaningless without a schematic with values on it. Many thanks for any thoughts.
I have just the same symptoms, but with so many capacitors broken in the PSU.

I didn't have time to check if that is the real reason, but I will try to repair the PSU as soon as possible.
 
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