iMac G4 15'' to HDMI display conversion

[zanedb]

Hi all, thank you for the detailed instructions and pinout. I'm planning to try this conversion soon with this HDMI breakout socket and am looking for a suitable power supply. I'd prefer something that can be kept within the base, just exposing an edison cable. Can anyone recommend a specific product?

 

[paardenkapper]

You could leave the original power connector in place and reroute it to a molex psu which you could place where the old psu once was. Or you could buy something like a pico psu and you only need to connect a power supply to a barrel connector which could be installed in the case. Just ideas.

 

[captainsideburns]

Hi, I think you need the molex adapter, because you need 12V and 5V. And if my memory works properly, USB can‘t offer 12V. I didn‘t use a resistor, but a step down converter, you can find links in this forum. Wish u luck!

Thanks. It seems I didn't get my USB regulator link correct. I was thinking about these, because you can apparently adapt the power output up to 12v.

USB Regulator

I'm trying to do this simple because I've never done anything like this before!

 

[paardenkapper]

Have you seen that the maximum output is 3 watts - this will not suffice for the display. You'll need at least 24w for the display.

 

[zanedb]

@paardenkapper, I understand you had to use a separate PSU as yours was broken. How difficult do you think it'd be to use the existing one? My G4 is still fully functional (I know, I'm a bit sad tearing it apart.. but I'd rather it see some use than none).

As far as I can tell, the step down to 3.3V happens on the logic board and one connection supplies power to the fan, speaker, and inverter (circled in white; inverter is the black cable on the left). So I'm assuming I'd still need to strip the inverter and use the step down resistor for the green inverter cable. But where to get 5V and 12V from? Can I take it directly from the PSU's molex connector that would've gone into the logic board? (circled in blue) And further, is it fine to run the PSU without the logic board connected?

Sorry for the beginner questions, I'm very new to this. Very thankful for your thread here, I'm learning a lot

 

[paardenkapper]

Hi zanedb, thanks for reaching out.
I remember that there were a few people who used the built in psu from a G4 iMac to power their sleeper build or monitor conversion.

Look at this post that was made in a thread I created before making the conversion:

https://forums.macrumors.com/threads/imac-g4-sunflower-not-starting-power-button-or-power-supply.2386249/post-32088694

In theory you have to bridge two pins to start up the psu and still need a converter for 3.3v from 5v - this would be fairly easy using a cheap buck converter.

BUT: If you have a working psu, which is kind of rare in this day and age I'd rather put it aside, sell it on eBay or whatever.

And yes: If you do not use a prebuilt board as was mentioned before (TMDS to HDMI) you'd still have to strip the wires.

Reconsider if you have a fully working unit right now I'd rather buy a known defective one for cheap and go from there.

 

[captainsideburns]

Have you seen that the maximum output is 3 watts - this will not suffice for the display. You'll need at least 24w for the display.

Thanks, this is the kind of detail that's beyond my current knowledge ...

Can anyone point to an off the shelf power supply from Amazon or similar that can do whats needed for this project?

 

[paardenkapper]

If you search for IDE power supply on any shopping site you like you'd come across something like this:

This will give you set you back 5-10 USD and provide 12V, 5V and GND. The next part you'll need is a step-down buck converter which looks like this and costs around 1-3 USD:

There is one side that goes in and one side that goes out. Put +5V on the IN-side and set the OUT-voltage to 3.3v.

To get all the right voltages from your power supply you should use a molex cable:

Cut off the SATA end or whatever cable you got lying around. Yellow is 12V (+), red is 5V (+) and black is your common ground (-). You will need some copper wires/cables in order to add voltage and ground to different places which are described above in detail.

I highly doubt that you'll find a better solution but maybe someone else can give a hint.

 

[Gregdotcom]

Hi Everyone,

first of all, thanks for finding out and creating instructions!

I have got an iMac G4, 15" and i would also like to use it as a screen.
I removed already everything and got access to the wires of the screen.

Sadly it seems that the wire colors are different from all your instructions and now i feel like i am lost

Left to right:
1. Wires: 4x wires (blue, green, red and orange?)
2. Wires (grey): 9x wires, these seems to be the TMDS wires, but they are not in a pair together
3. Wires (Inverter Cable): This seems to be me straight forward: (blue: 12V, red: 5V, green: 3,3V, black: GND, rest is not used), i have a Stepdown for 12x to 5v and 12 to 3,3v.
4. Wires: 4x wires (2x Red, green, black)

I already tried to connect them to the HDMI Pinout adapter, but then i decided to ask the expert before i fry the screen

Can you please help me out how i can find out the right assignment to the pins?

I was also thinking about to completely replace the screen, but because it is working fine and 1440x900 resolution i would be in love to still use the original.

Thanks already for your support!

 

[paardenkapper]

Hi Gregdotdom. The first thing I noticed is that you removed the connectors from the cable tips and this could possibly lead to poor image quality but let's assume it works out.

The TMDS cables should come in pairs of three it is packaged together but all channels are separately bundled and there is one greyish in every bundle. If you take a look at the graphic on page 2 of this thread you should be able to put it together. I also provided photos of my working build with everything connected.

You only need two packs of wires from the display: The inverter and tmds wires. The other one is for the LED I guess and I didn't use it.

My guess is that as the resolution of the 15 inch G4 is not 1440x900 but 1024x768 you got the 17 inch version which has different wiring smh.

This extensive thread should point you closer to your model:

GUIDE: Step by Step 17" iMac G4 TMDS to DVI Conversion - 800mhz and 1/1.25 Ghz Necks Completed

Mac Mini identifying monitor as "iMac" This is a step-by-step detailing the process of converting a 17" iMac G4 to a useable LCD with ...

www.dremeljunkie.com

 

[zanedb]

Started the conversion today. I figured since the desired initial power input is the same as SATA I could just use the SATA power output that’s included in the onboard PSU, with a step-down buck converter supplying 3.3v. I haven't tested yet, but is there anything else I should know about that approach? @paardenkapper, you had mentioned needing to bridge two pins to start PSU without the logic board—anything you could point to there?

Ran into an issue upon starting the HDMI breakout wiring—I realized I may not have spliced the correct TMDS wires (pic 1, bottom; top is what I believe to be inverter). Notably, there’s several green and red wires, I can’t find a purple one at all, and the brass-looking sheath that separates the data sections seems to be missing, making it hard to follow the previously supplied pinout. I pulled them from a larger plastic connector where the gray and black wires met (pic 2, pre-splicing). Should I splice further up on either the gray or black wires? Or is it something else entirely? Pic 3 shows my current status; sorry all the wires are black, I know it's hard to follow. Thanks again everyone.

 

[paardenkapper]

Started the conversion today. I figured since the desired initial power input is the same as SATA I could just use the SATA power output that’s included in the onboard PSU, with a step-down buck converter supplying 3.3v. I haven't tested yet, but is there anything else I should know about that approach? @paardenkapper, you had mentioned needing to bridge two pins to start PSU without the logic board—anything you could point to there?

This is only hearsay to me. I have read several times that some people use the internal power supply but for most upcycling it to a display is because the psu is broken. As you can read in the post before my approach is to use an external psu. If you want to read more about the G4 psu please look here http://www.dremeljunkie.com/2012/05/17-imac-g4-native-psu.html and http://www.dremeljunkie.com/2012/05/20-imac-g4-native-psu.html

As stated in these pages the psu should be live as soon as mains power is connected!

In an ATX psu you can bridge pins 3 + 4 (PS_ON and COM) to make it run all the time.

And again: If your PSU is working you should leave it intact and use an external one. First because they are rare and prone to fail

Ran into an issue upon starting the HDMI breakout wiring—I realized I may not have spliced the correct TMDS wires (pic 1, bottom; top is what I believe to be inverter). Notably, there’s several green and red wires, I can’t find a purple one at all, and the brass-looking sheath that separates the data sections seems to be missing, making it hard to follow the previously supplied pinout. I pulled them from a larger plastic connector where the gray and black wires met (pic 2, pre-splicing). Should I splice further up on either the gray or black wires? Or is it something else entirely? Pic 3 shows my current status; sorry all the wires are black, I know it's hard to follow. Thanks again everyone.

I think you're on the right track here. Just roll back the shielding some more as you can see in my photos you'll have to create some wiggle room. Peel back a bit and you should see that there are five separate cable packages inside the TMDS package and then start by connecting the HDMI breakout.

If you're not sure about what goes where please take a look at my diagrams and photos and it'll all fall into place.

 

[zanedb]

Power is done and I’ve confirmed the correct voltages with a multimeter. As I was using the existing PSU, I was able to bridge pins 1 → 6 and 9 → 14, and using a step-down buck converter take 12v from pins 3/11, convert to 5v, then bridge to 7/15. Now the molex connector in line is functional. I stripped the ends of those wires to take 12v, 5v, then used another step-down buck converter to obtain 3.3v. Dremeljunkie was massively helpful—thank you for the link.

Now on to data.. Pins 1-12 seemed straightforward, all coming from the black TMDS cable and alternating red (+), black (gnd), and green (-) wires for brown, blue, green, and red sectors. It’s 15, 16, and 18 where I can’t seem to make my cables match your diagram. I can’t find gray, pink, and purple cables; I’ve compared to your photos and nothing matches those colors. Pic 1 shows my current wiring (note that I’ve used every cable in the black TMDS cable for 1-12), pic 2 shows the spliced options available in my gray cable (seems like that’s where I’d find those last three..?).

Further, pin 18 seems to be +5v supplied by the HDMI cable when connected; do I want that in series with the 3.3v? It just ends up increasing the voltage on the whole line (& backlight brightness) when HDMI is plugged in.

 

[paardenkapper]

I have revisited my display and I think that my diagrams might be slightly off.
In fact there are five wire bundles coming from the TMDS bundles. So sorry for the confusion everyone.

Here I have recreated the wiring table as it is currently used in my project - I hope this helps you along.
Even though I think that you might have a different iMac model - maybe 17 or 20 inch which has different wiring or voltages as stated in my posts above.

The first video in my post is the one I was referring to when starting this project.
I never really received any feedback on that.

 

[paardenkapper]

As an update: I completely rewired the power cables inside the iMac to clear up the situation and confirm my information. Also here is an updated version of the HDMI and power wiring scheme.

This is how it's working 100% and I really hope this is helpful to someone.

 

[JafRay]

Created an account just to say thank you Paardenkapper !
I'm am currently using this conversion project as an excuse to design PCBs

 

[mctest]

First of all, a great thanks to Paardenkapper for posting your work with detailed G4 15" pinouts and wiring scheme!!!
Yesterday I finished my conversion using an original Apple DVI to HDMI adapter and the new iMac G4 display works like a charme
The only problem occurs when the external computer switches to sleep mode, shuts down or just by removing the HDMI cable. The display then freezes each time with the last screen image in darker color and a bright white bar at the top, as you can see in the photos. When returning from sleep mode or by reinserting the HDMI cable, the display quickly resumes normal operability.
Any ideas what is causing this and how to fix it?
Thanks in advance from Switzerland for helping me out in this case.

 

[paardenkapper]

Grüezi mctest. You're welcome!
Just to make sure - did you attach a DVI port instead of HDMI or why did you use DVI to HDMI to USB-C?

In my case when I disconnect the display the screen fades to grey as well but without the white bar.
If you can live with this circumstance I'd just accept it :-D

 

[mctest]

Grüeziwohl 😃 but you are living in the Netherlands, don't you? I think so because 'paarden' is the word for 'horses', isn't it? One of my aunts comes from the Netherlands so I know some little words.

Yes, I attached the LMDS wires to the female DVI port of the Apple Adapter which has a male HDMI output.
First I wanted to order an HDMI breakout board, but remembered that I have this old adapter somewhere around and that it would be very easy to fit the small wire pins into the female DVI input port.
USB C in this case is only been used for the MacBook Air M1 not having other ports.

Thanks for your feedback, I only have the 'burning in' screen problem in mind, so perhaps it would make sense to find a solution for the display going to sleep mode, too.

 

[paardenkapper]

No I am from Germany but I'm Dutch-positive ;-)

I am no expert in display technology but I think the fading is normal because the display is still powered on but there is no signal. In regular displays you would have a dedicated controller to show a message or a control menu for example but in this case it's all bare and directly connected.

You could buy a dedicated controller for the screen (LG or Samsung probably) and have HDMI, VGA and on-screen controls. Or you can use an arduino to build the logic I guess. Let me know!

 

[mctest]

Ah cool, I am a german native but live in Switzerland many years.
Dann können wir ja in Deutsch schreiben 😀, but would be not so good for the forum.

Beginning the mod, I was also thinking about a dedicated controller for the panel (already did it with an 2010 iMac for a friend of mine). But I don't wanted to make too much effort by taking apart the whole display and neck.