20" iMac G4 TMDS-DVI Pinout - UPDATE: CONFIRMED

Update 11/2/2011: I have finally solved the native inverter issue and as a result, used the same method I used for my 17" Mod and can now say that this pinout works.  A guide will be coming in he future as well.

I have received a request for the TMDS-DVI pinout of the 20" iMac G4.  Just like the other iMac G4 panels there is a TI chip which converts TMDS to LVDS, so with a DVI cable and power source the native lcd should be usable with any DVI compliant source.  However, the caveat here is that I have been unable to get the native inverter to work properly.  So, while there may be an image, with no backlighting - it will be very difficult to see.

That said there are work arounds:
1) Aftermarket inverters (works great, needs only 12V, 5V and ground), but I have not found one thin enough to close the case completely - but if you don't mind a little buldge, this does work fine.
2) Alternate Backlighting (LED etc)
3) Get the native inverter working:
       What I've learned: It requires a 24V and 3.3V line.  The Dimmer seems to work backwards of most where it requires 3.3V for maximum brightness.  There is certainly a way to do this, but I have already damaged several in my attempts and I felt that even if I got it working, finding adequate power sources that would work together would be difficult.  You would have to use a powersource that has a 24V line such as the native power source for the 20" or the iMac G5's.  I didn't want to have to "turn on the backlights" with a separate switch.  The Apple Cinema Display also uses a 24V line, so I initially thought about using its power brick.  Thats when I realized that the power wiring including a brightness switch and on/off were already done for me by using the 20" apple cinema display itself.  Conveniently, its the same size including thickness and weight as the iMac G4 20"s monitor and housing.  This led me to my Apple Cinema Display/iMac Mod, which has exceeded expectations so far.  But, I can understand the desire to get this as "genuine" as possible.

iMac G4 20" TMDS-DVI Conversion

So here is the TMDS/DVI conversion chart.  This is based on the LCD panel: Id Tech 20" LCD.  Notice there are significant differences from the 17".  This includes different placement of the shield wires and some grounds as well as higher voltage requirements.  Because I never got the inverter working, I have not verified this, nor do I plan to.  As long as ID tech did not misprint the specs, there is really no way this could be incorrect, but you never know until you try. Update: Never say Never

Inverter Frustration

After success with the 17" I was hoping good fortune would carry over to the 20" mod.  However, the 20" Inverter has continued to be a problem.  As the DVI/TMDS is essentially the same as the 17" (with just extra power to the panel) I don't anticipate this being a problem.  So the task of turning on the backlights seems simple enough.  Here are the problems and failed solutions I have tried:

The original inverter is remarkably flat  and specifically designed to fit in the monitor chassis. I have not been able to get consistent even lighting.  It does require a 24V line so I am using a separate DC line to power the 2 24V lines. As you can see I have gotten some response.  By giving 12V to the on/off it can become very bright.  But, this is neither stable nor even.  Without a doubt there is some way of mimicking the iMac's signal and use the native inverter.  But, I am not an electrical engineer and the entire purpose is to keep this as simple and stable as possible.  I have thus moved on in an attempt to find another solution.



Aftermarket inverter.  Available on ebay are several relatively cheap universal inverters that can support 6 ccfl lamps with a 4pin and 2 pin connectors.  This one was $30.  I'm not sure if the picture does it justice with the glare, but the screen is evenly lit and bright.  Whats more is that the connections are very simple.  There are two 12V rails, 2 grounds, one on/off - which takes 5V, and an adj/dimmer.  However, while much narrower, it is longer and more troubling, slightly thicker than the native iMac G4 inverter.


I thought it may be possible to make it fit in the case with some alteration using a multi-max dremel.  The back of the monitor housing uses "raised x's fit the monitor tightly.  I thought that by removing these raised areas I may be able to create a little more room for the thickness of the inverter.  As you can see below on one side the "Raised X" has been removed and sanded down (this does not damage the back or outward appearance at all).  I then placed the inverter in at several angles (to try I didn't use the protective plastic covering).

 As you can see it just doesn't fit .  I don't want to press down firmly, screw it in, and leave it under pressure.  I know it may not look like much but it extends around the entire side of the monitor.  As I was hoping to make this a touch screen as well, the monitor is likely to be somewhat unstable in the housing.  So I looked for other 6ccfl inverters that may be slightly thinner.

 Here are 5 inverters that are designed for 6ccfl monitors.  From top to bottom: an iMac G5 inverter, aftermarket on ebay (4pin/2pin), aftermarket on ebay (2pin x 3), a 20" apple cinema display inverter, and the aftermarket inverter used above.  The only one that the case would close with (even with the dremel modification) was the cinema display inverter.  However, it still took a little force and unlike every other inverter pictured, this is not a straightforward inverter (there are actually 8 pins - more than the iMac).

 I had also thought about using LED lighting (which does not require an inverter) however after a brief test of constructing my own led rail, I was not happy with the results (uneven lighting).  Putting the iMac's LCD onto a commercially manufactured  20" LED backlit montitor would likely work very well.  However, they simply do not manufacture 20" LED backlit LCD's in the 16:10 (1600x1050) orientation, which would be required for this mod.

So, I am left with 2 options: Continue to search for a solution to the 20" backlighting problem or to complete the all in one mod using the already built 17' monitor assembly.  I do have another idea for the 20", so I am not giving up yet.  After using my previous 17" mod for sometime, I do have to concede that a 17" monitor seems awfully small these days and a 20" would be preferable.  Plus, I have located a 5 wire resistive 20" touchscreen which would be ideal for this mod.  If anyone has any ideas, tips, or suggestions, they would certainly be appreciated.