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.