Saturday, March 5, 2011

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

12 comments:

  1. even if it looks bad i just wnat to check i wired the 30 pin right so could you make one of those charts for the inverter and anything else i need for the 20" connected to a modded atx power suplly ie i get 3.3v 5v 12v i could combine 2x 12v rails to get 24 right?

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  2. No - voltage doesn't work like that. Two 12v cables are 12v putting them together does not change this. You need a transformer to change voltage (a step up transformer to increase and a step down to decrease).

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  3. wahts the aftermarcket inverter that would work with this monitor

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  4. If you go on ebay and search for 6 ccfl inverters you will see several options. I can not verify which ones work for this monitor specifically. I didn't really try after I realized I could not get them to fit inside the monitor casing.

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  5. The yellow wire for the inverter is for the dimmer. It's a PWM signal. 25kHz. Amplitude is 3.3v. Positive duty cycle ranges from ~18% to 100%. 18% is 8us "on" pulses within the 40us cycle. The purple wire is for turning the monitor on and off. So I was wondering is you found anything else out about using the 20" screen. So in your chart above, there is the black wire that contains TMDS wires 1-13 and there is also the grey wire. I chopped the grey wire and checked all the signals on a scope and didn't find the same outputs. The red, black, and white wires had 3.3v. Everything else in the grey bundle had noise on them. The purple, yellow, and orange wires did not have 12v on them. I'm looking to use this monitor as a second monitor for my laptop. I'm not sure what the deal is, maybe I am doing something wrong. I've got everything basically figured out except this grey bundle (wires 14-24). Have you any more information about this project? Thanks.

    -Sam

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  6. Hey Sam, thanks for the info. I agree with you that the purple is on he on/off. The yellow is probably a PWM signal, but I had thought the orange wire was responsible for dimming. What are you feeding the yellow and orange wires specifically in order to use the inverter? I could not get the inverter to work so I used a work around with parts from an apple cinema display and there was a weird quirk involving an extra wire. This is discussed in this post:

    http://dremmeljunkie.blogspot.com/2011/07/20-imac-g4-inverter-pinout-not-tested.html

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  7. Sam, in terms of the gray wire, it contains the control signals for the EDID (extended display identification standard) For DVI specifically the clock(black), data(white), power(red), and ground(gray). These must come from the computer/graphics card via DVI(or HDMI). This tells the LCD what it's connected to and turns it on. Just connect them to the corresponding DVI pin numbers that I listed in the chart. In terms of the the other power and grounds this comes from the actual ID TECH specifications for this panel. Which indicate grounds at 19,20, and 21 and the Vcc input voltage of 12v at pins 22,23, and 24. Perhaps there is some feedback that the iMac is not getting so it is not sending power to the panel. This panel is powered by 3 12V lines according to its manufacturing specs, I would verify that your pin colors correspond to the pin numbers listed above (variation has been seen before) but there should be a 12v VCC that isn't accounted for.

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  8. Sam, some one has posted an online copy of the manufacturers specs. You can review them here:

    http://fredriksjoholm.se/slira/hacks/g5lcd/elecfans.com-M201Z2.pdf

    Hope this helps

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  9. Thanks for the quick response. Yeah, I was thinking there might have been some feedback as well. All my colors did check out fine with your chart so I'm sure everything will work out fine. Just thought I would double check with you before I went ahead and sent 12v to this thing. Thanks again.

    -Sam

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