Saturday, May 7, 2011

A Genuine iMac G4 All-In-One

Although I thought the previous 20" iMac G4 / Apple Cinema Display came out very well and it has become my most frequently used desktop, there were compromises that I had to make.  The two biggest ones were externalizing the computer (abandoning the all-in-one concept) and using the external housing of the apple cinema display.  While I think it looks good, it still is not the classic 20" iMac G4.  While working on a different mod, I realized there are two things I overlooked while designing and building the previous mod that would allow a genuine 20" iMac G4 all-in-one with an updated intel processor.

I was working on a project which involved using some of my spare components with a broken shell of an iMac G5.  These were mostly unused pieces from my iMac G4 mod.  This predominantly included a LG LM201W03 monitor from an apple cinema display (although the G5 I believe uses the same panel with some variations).   And the ECX board which uses a P8700 Penryn Core 2 Duo processor (the current mac mini uses the P8600).

Comparison of native iMacs DVD/HD to size of Bluray with ECX board
As it is the size of a 3.5" drive and it has its own  Compact Flash slot to use as a SSD, I had hoped to slot this into the G4 in place of the existing hard drive and create an all-in-one that even kept the DVD drive. However, when it booted it would not display at the required 1680x1050 resolution of the cinema display.

I had thought that the ECX board simply could not output at the requited resolution.  The ECX board has a PCI express x 4 slot, I attempted to add  a PCI express x1 Ion graphics card, while this fixed the resolution problem, the ECX ples the graphics card no longer easily fit into the iMac G4's chassis.

I was wrong.  The ECX board can support the resolution, it seems to have a quirk with the cinema displaythat it detects it as multiple monitors one of which is a lower resolution.  When I manually adjusted the resolution in windows and turned off the "phantom display", the display became full size.

Although I have not minded having the external mini, this board gives essentially the same power as the newest mac mini plus it has 4GB of ram and uses compact flash for a SSD, if its "hackintoshable" - I do not know yet.

I still did not want to alter my old mod in any way that may damage it, nor did I want repeat the same cinema display hack.  I wanted to use the existing iMac G4's monitor housing.  This brings me to the second thing I had overlooked.

I decided to use the Apple Cinema Display enclosure because the iMac G4's monitor enclosure fits the lcd panel and its specially made super thin inverter and NOTHING else.  And I was never able to figure out how to use the native G4 inverter without the G4 motherboard itself.   For the first time I decided to compare the apple cinema display's inverter to the iMac G4's to see if there was any way the cinema display's inverter could fit within the G4's monitor housing.  Thats when I noticed the 8pin connectors were almost identical.

The iMac G4 only uses 7 of the 8pins, however when the one was not connected, it would not turn off immediately when the computer slept, so I will have to make sure I have one extra wire going through the neck to use all 8 pins of the inverter.  To my surprise when all 8 pins were connected it worked perfectly.  If there was any difference I was unable to see it.

Being able to use the native inverter meant that I could use the native iMac G4's monitor housing with the Apple Cinema Diaplay if I could find a place for one more board - the LCD controller board.  The controller board is very flat but is not flat enough to fit withing the housing.

Comparison of iMac G4 bottom with native motherboard vs. ACD LCD controller
Unlike the inverter whose high voltage cables should not be extended through the neck, there is no reason why the lcd controller can't be placed in the base and its cables extended to both the inverter and LCD panel.

As it is just as plat as the native motherboard which I will not be using it can fit at the very bottom of the dome.

The only true nuisance with this is that although both panels use TMDS signaling, the neck needs to be modified.  The existing Inverter wires can stay, but by placing the controller in the base, there are a total of 27 wires that need to extend up to the neck.  The black and grey wires combined have 22 wires.  Plus I needed one extra wire for the 8th inverter wire, making a total of 28 wires.  To add additional wires, I did take apart the neck and change the microphone, lcd wire to an additional grey iMac TMDS cable that I had from a different neck.  Once I had all the connectors soldered on I was able to put the inverter and lcd on one side of the neck and the lcd controller and ecx board on the other.

Unfortunately it does not look like I'll have room for both a power source and a DVD/Bluray.  I will be able to fit one or the other.  Right now I'm leaning towards keeping the drive and having a power brick external.  I want this mod to look as genuine as possible, as such I'm forgoing anytouchscreen option.

Powering it on revealed a clear image:
Now to internalize it into an iMac G4 20" shell to see if it will fit.  This is the most hopeful I've been for a genuine iMac G4 20" all-in-one with modernized hardware.

As always, feel free to ask any questions.


  1. Hey, Why is it that the High voltage cables can't be extended through the neck? Could that be the cause of my video issues?

    I'm still a little bit unclear. Did you end up using the custom inverter that was built for the G4, or did you manage some other trick to get it to work?

    As always, thanks for your help

  2. Its not that you can't use high voltage cables but it causes two problems. For one, the high voltage will interfere with the video signal unless everything is very well shielded.

    Secondly, there is a potential safety hazard.
    I have forced extra wires into the imac neck and jammed it closed - and although it works when I have opened the neck back up you can see some sign of wear on the wires. What scared me is that if you wear through the coat the high voltage could arc to the metal neck and electrocute anyone who is touching it. Here is a video that demonstrates this effect:

    This mod actually uses the native inverter - not only that but when you see my next post you can even use the native lcd glass. And I'm happy to help anytime.

  3. Dave, I just realized who you were from your website. Its awesome to see another iMac G4 obsessed modder back in the fold. I just read your current progress and think I have some suggestions. I will comment on your blog.

  4. HI i have a imac 20inch intel version.. but the logic board is dead.. i wanted to rebuild it and use a normal laptop motherboard, bust still keeping the original 20inch screen.. is such a conversion possible?