Monday, February 1, 2010

20" iMac G4 Mod - TMDS to LVDS (Not Recommended)

UPDATED (11/5/11): I have condensed all the posts that involve this mod to this post for better organization.  Again this method is unstable and potentially dangerous.

This method is no longer recommended as I have since found much better, cheaper, and safer. ways of doing this. there is a safety issue and I do not want to see anyone get hurt.  I am tempted to take this post down but I do believe there is value for people that want to convert from TMDS to LVDS.  The dangerous part of this is the inverter wires.  As I placed the inverter in the base I lengthened the wires that connect from inverter to backlights.  Once the current passes through the inverter it becomes very high voltage.  The 20" version has 6 backlights when you add these cables (12) to the LVDS cables - you have to run more wires through the neck than it can really hold.   What this results in is wires that are rubbing against the hinges of the neck.  I started hearing an electrical humming sound and became concerned enough to disassemble this mod.  Recently I decided to open the neck apart to salvage some wires for parts.  I saw clear evidence of wear to the shielding of the wires.  If the shielding wears on the inverter wire it could easily arc to the metal neck and electrocute anyone who touches it.  Here is a video someone has made demonstrating the ability of the high voltage in the inverter to backlight cable to arc.
Inverter CCFL video

Original Post:
Completed LVDS 20" iMac G4
I. Overview

The biggest question is if you want to use the original monitor which uses TMDS signaling or replace the monitor with one that uses the more standard LVDS. I decided to replace the panel with a standard LVDS panel.

The next decision is size, I decided to go with the 20 inch iMac here. Some people prefer the 17 inch model, but its all personal preference. As long as you are careful about monitor choice this mod is actually easier on the the 17 inch model. Remember to choose a panel that is 16:10 not 16:9.

I ended up going for the LG 204WT. Its a good monitor, has the right aspect ratio, and because I burnt out my last one, I had spare parts. I ended up finding a refurbished one for $90 on ebay. This monitor has some other nice features for the mod. It has a small keypad (the power and menu buttons), it uses an LVDS wired cable, not a ribbon cable, and the power source can fit into the base. Because the base has four brackets that come down around the DVD drive, you can use this as a guide to see what will and will not fit. So if its bigger than a 5.25 Drive its prob not going to fit.

Another decision is to make this an all in one or not. Because the power source and inverter need to be in the base there is little left over room for any computer components.

There are instructions on how to take apart the iMac G4 online and I won't go into specifics but to say you need to seperate the neck from the monitor and base. Almost everything in the base will not be used for this modification. Most of this mod revolves around the neck. To take apart the neck I used a mini screwdriver set and taped two together. You may need two sets and someone to hold the other side of the bolt steady while you turn initially. The neck is not difficult to take apart. This is shown below:
Tape 2 together for 2 sets

II. Wiring
Again, Do not wire the inverter to CCFL through the neck.  It is OK to keep an inverter in the monitor housing and lengthen the cable to the inverter.  But, I can no longer recommend lengthening the wire from the inverter to the CCFL backlights through the metal neck as this is a high voltage wire and there is risk of this arcing to the neck and electrocuting anyone touching it when this happens.

Remove all of the iMacs native wires.

You should first put through the inverter extensions as they are the thickest wires.
The small two pin inverter connector can fit through the neck and does not need to be removed.

There are 6 CCFL backlights (each with a high and low voltage line). The 4 pin cables support 2 CCFL lights and the 2 pin cables support one in the 20 inch monitor. For the high voltage lines, I decided to use heavy shielded inverter extension cables. These wires are very high voltage and high voltage can arc if exposed. The last thing you want is an exposed wire arcing in a metal neck. It can be VERY dangerous. I bought 6 inverter cables from an HP Omnibook on Ebay. They are 15" It takes two extension cables that link in the neck to make it all the way through..

If you decide to use an LVDS panel, you should replace all of the wiring in the neck. LVDS uses a series of paired wires (for the most part). Most LVDS cables have a 30 pin connector of which usually 27 wires are used. In addition, you have to lengthen the inverter wires, that is two wires each for the two inverters. You also have to lengthen the low voltage lines for the inverter as well. As you can see that makes a total of 39 wires that have to go through the neck. Things will get VERY crowded in there.

Remember to be cautious with an open neck, the spring can be dangerous. As long as the neck is open you should tape it down.

For the LVDS cable, you can either order an LVDS cable online or you can make your own. You can use 30 gauge kynar wire. Because I had several LVDS cables from previous mods, I decided to use these. I ran 27 70cm LVDS wires through the neck. The advantage to using LVDS cable is that they already have the pins on them, which makes soldering easier. You have to remove all the pins from the connectors, you can only fit wires through the neck, connectors will not fit. (Except for small inverter connectors). As you run the cables in make sure you label them on EACH END. You will need to know what to solder where.

For the low voltage inverter cables I chose CAT5 wire, I simply cut apart an ethernet cable, stripped it and ran the wires through the neck.

With the LVDS wires through
III. Soldering
With the 27 LVDS wires, the 8 + 4 inverter wires through, you can close up the neck in can be difficult to close and you may need to use your screwdriver as leverage. You should try to add shielding to as much of the wiring as possible. However, this is difficult as there are so many wires.

Soldering the LVDS cables
I ran the 27 LVDS wires through the neck, however they need to be extended at both ends and end in connectors. I soldered the top (monitor part) to another 50cm LVDS wire and then the bottom to the existing LVDS cable that came with the monitor. If you do not have extra LVDS cables. I'd recommend simply running 120cm of Kynar wire through the neck, then cutting the existing LVDS cable in half and soldering each wire to its appropriate match at each end. Remember to label all the wires.

I also decided to cut off the 4 pin inverter connectors from the native iMac G4 panel and the native inverter (I did not want to have to cut the wires on the LG panel to attach. I then attached these connectors to the the inverter cables. Pink cables are high voltage, white cables are low voltage.

Soldering the inverter attachments
This is a good place to check the connection. Disassemble the monitor to expose both LCD controller board and the inverter and power source.

First I tested the connection.

Then I added the inverter cables.

 In both tests there was a clear image that ran through the neck. Now that we know it works, we can assemble the base.

IV. The Base

Run the wires through the base and screw in the neck. Connect the wires to the LCD controller and place it at the top of the dome.

Then connect the inverter cables to the inverter and power source. Use screw to attach the power source to the dome.

For the drive, you have to modify the cady, cut the top off (where the hard drive would normally sit). Leave only the side rails and attach them to the drive then screw in the drive. This way the monitor components are protected at the top of the dome.

Wires at Top of Dome
LCD Controller Installed
Power Board Installed

Ready for LCD

You will need to tape the wires flat against the back so you can close the monitor eventually. Its not pretty, but it works.  Close up the monitor and we're done.

Although this mod does not leave room for the touch screen, I can say that I am significantly happier with the way this turned out. This mod leaves me with an external blu-ray player and plug and play monitor. It is clean and simple without any visible wires or shelves on the back of the monitor.  I know this does not show every single step, so if you have any questions feel free to ask.


  1. You said there were instructions online for taling apart the Imac G4. would you tell me where. I need to replace the inverter board, and I don't know where it is, or how to get there. Thanks

  2. I can certainly help you with that. For the 17 and 20" you have to remove 3 screws using a #6 torx screwdriver from the bottom of the monitor casing. Then remove the front bezel from the bottom first. The front bezel contains the actual lcd. For the 20 inch model the inverter is a flat square which is screwed to the back of the monitor casing. For the 17 inch it is a 2 - 3" long 1/8" wide piece next to the lcd on the front monitor bezel. The inverter is easily recognizable by the white and pink wires connecting from the inverter to the lcd. There are 4 wires (2 on each end) in the 17" and 8 wires (2 4 pin connectors and 2 2 pin connectors. Replace this with your new inverter and you should be all set.

  3. Hello, do you know is there is a difference between the display neck on the 15" 17" and 20" imac?
    I have an imac 15" but want to move one to a bigger screen. I have found the front bezel and back cover for the 20" imac but im not sure the display neck will hold.

    What do you think? can't fint any info on this matter..

  4. Unfortunately they are different. The different monitors do have slightly different cables. But, the biggest difference is the weight they can support. The 15 inch neck will not be able to support a 20" LCD.

  5. thanks for the answer. I have found a 17" screen case with arm , so my next question is, is this a "stantard" 17" or is there something I need to be aware of when looking for a new screen?

  6. And on more thing, If I get hold of a case with arm for an 20" display, do I have to find a 16:10 monitor or can I use a "normal" 16:9 one.. I have been reading and searching the web for hours now, and cant seem to find a final answer. Thanks again!

  7. Only a 16:10 monitor will fit in the existing 20" monitor frame. Remember though that this is also true for the 17" monitor as well. Good luck

  8. Love the mod. I'm staring down my FP G4 and considering the options. I'd like to try the atom route and circuit bend the imac's signal cable to work with a standarized vga output. What will I find when I open the case and trace the signal cable from monitor to logic board? Is it some crazy proprietary connection and do you think it would be bendable / solder-able to my application? Open to a chat? oavcATtelusDOTnet

  9. I'd def be open to a chat. I can tell you that the 15 inch is circuit bendable but things get more proprietary and difficult with the 17 and 20 inch varieties

  10. Mine is a 15". I'd love to bounce some ideas off you but I can't find an email for you. Mine is

  11. I know with my iMac G4 when I opened up the 15" arm as a test I managed to get the spring inside to pop off quite easily before I even got the casing removed and once it was popped off it was impossible to replace it. What are your suggestions for keeping the spring on and possibly for replacing it in the arm when it does come out?

  12. Love what you have done. I have an iMac G4 15" and an iMac G5 20" laying around. I am wanting to put the LCD from the 20" in the 15" do you think this would be possible or do you think I would run into a lot of problems? Also if the 15" arm could not support the weight could I buy a 20" arm and just swap them out? Let me know what you think of this. Thanks.

  13. Thanks so much. The iMac G5 would be WAY to heavy for the 15" and even 20" necks. Even the iMac G4 20" Monitor housing weighs about 11 pounds. The iMac G5 weighs 22 pounds. Even if you took a couple pounds off for the stand it would still be too heavy.

    Also, while you can switch the necks out, there are differences in the base between the 20" and the other G4s. The base was given extra weight to support the heavier LCD. So even if you got the weight to work out on the arm, it would likely tip over without extra weight added to the base. Hope this helps.

  14. so, i'd like to build a new computer into a g4 17 inch model. what size/type of motherboard would i have to purchase? also, what is a good disk drive for this machine? i don't want bluray. just a dvd burner. also, can i get a 16:9 display, and just have some extra screen glass on the sides, or is it too ugly like that, because i can't find any 16:10 displays.also, does anyone know the max weight that the display arm can hold?

  15. also, do i even need to get a new screen? or can i just use the stock one? if i can use the stock one, can i connect it to the vga out on a mobo i add to it, or would it have to be dvi? or would it just be crazy to attempt? thanks

  16. Hello thanks for reading. If you want a disk drive - not even a mini itx will work. I discuss board choices here:

    Yes you can use the stock monitor and it is DVI/HDMI only. I discuss all the different ways this mod can be done in this post.


    This should help answer your questions

  18. hey. i just herd of a new mobo type from intel called thin mini itx. it is 2 cm high MAX, with a 2.5 cm tall MAX I/O shield. could this work in the base if a g4 imac?

  19. i forgot to mention the model for an easy search. it is:
    Intel® Desktop Board DH61AG

  20. If you plan on using an optical drive then it wont fit. Really nothing will fit at the bottom of the dome. You need a 5.25" drive if you want to keep the original form and function. A slim drive won't have the powered tray to press the door open. You could try to rig something up, but I still wouldn't advise it.

    Two problems: for one it's putting a square peg in a round hole. The original board was round and had holes in it for the four pegs to come through. Though a mini itx form will fit - it barely does but it leaves no wiggle room in terms of length/width. Unlike the round board where the ports are on the edge where the wont hit the drive - the mini itx's rear ports will get in the way of the drive.

  21. The second problem is the bigger one - you are going to need a heatsink/ fan for your processor. There is probably less than 2cm of room below the drive. Any heatsink alone will be larger than this. Even if you could fit it the fan would be up against the drive. In the original the convection cooling plates were on top of the heatsink - so the drive physically sat directly on top of the mobo. Very difficult to reproduce. See this post for details:

  22. Hi, can you tell me what size screwdriver you need ti get the arm apart? Thanks. I am trying to make a lamp out of an old G4 imac

    1. A special tool was made, but that is hard to come by now. I simply used a standard mini screwdriver set and taped the 4 smallest together in 2 pairs as detailed above

  23. Hello! Thanks for this guide! But, I have a question. Do you know of any 15 inch LVDS panels that would fit correctly in the iMac G4 15 inch model? Thanks in advance!

  24. To be honest, the 15" is the one I am not very familiar with. However the modder pgee70 did this in a mod he put on YouTube. Search for iMac g4 snow leopard on YouTube. He may have mentioned it or you can ask him.

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  27. Hey how do you put the arm back together again?

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