Saturday, March 13, 2010

17" iMac G4 LVDS Conversion Process

Again, this is no longer the preferred method, the TMDS to DVI is better in every way.  To keep my blog better organized, I have combined several posts into this one post detailing this conversion.

I. Parts List
This is a list of parts that I will be using to construct an iMac G4 17" Touch Screen which will be used as an external touch screen monitor for a separate computer.  I am waiting on delivery of the monitor.

1)Broken iMac G4 shell.  (includes monitor back and front bezel, 17' iMac Neck, superdrive cage, base with faraday cage.)

2)Monitor - HANNS G HB171DBB (This is the model with DVI, its 16:10, uses an LVDS wire and not a ribbon cable)

3)17" 16:10 4-wire resistive touch screen.  Purchased from easyworldwidetrading (Hong Kong based company) on ebay

4)Wires: A)For LVDS cable -  shielded cables from the neck of a 15" iMac neck and 17" iMac Neck.  Depending on how many wires the LVDS cable on the Hanns G has.  The TMDS in the iMac cable uses paired wires with a third ground that wraps around the pair (Most LVDS cables have paired wires with a few ground wires mixed in and then 3 12V cables).  I would prefer not to use the ground wires for signaling.  The 17" TMDS cable in the neck has paired wires (which are >30 gauge) and are very difficult to work with in the black cable and larger wires (28 - 30) gauge in the grey cable.  The 15" neck cable has 28 - 30 gauge wires (about 20 including grounds and 15 excluding grounds).  I will likely then use both the grey cable from the 17" and the only cable from the 15" (remove the black cable).  I am interested in using the existing cables because they were designed to withstand the stress of movement in the neck.  If I do have problems with this I may purchase additional long LVDS cables or use 30 gauge Kynar wire.  I know this is confusing but I will include details and pictures of this when I start this mod.
             B)For 4-Wire Touch Screen - shielded controller to inverter cable from the existing 17" imac neck (this has 6 wires, I will be using 4 of them).  This is really nothing more than usb wires and they appear to be about 24 - 26 gauge.  If there is a problem with these I will use cat5 wire, but again I am trying to use as much well protected native iMac G4 wires as possible to increase the longevity of this mod.
             C)For Inverter to Backlight Cable Extensions - High voltage pink and white 15" inverter extensions x 4.  I have six of these but if you place them right 4 should be OK.  The extensions I'm using I bought on ebay (they were from HP Omnibook laptops).  They worked well with the 6 backlights on the 20" monitor.  Because the 17" only has 2 backlights (one pink and one white wire per backlight) and it takes about 26" to make it from the corner of the monitor to the middle of the base, 4 of these would be sufficient.
              D) Extenders - 6" VGA extender, 6" DVI extender, 6" three prong AC power extender, USB extender.  These are just short male to female cables that will allow me to have ports at the back of the base to attach cables to and not just random cables coming out the base.  This is actually very important.  If the cables get pulled from the outside you do not want them to pull at and damage the lcd controller and power source inside. 
              E) Buttons/Keypad - I am hoping that the keypad on the Hanns G is small enough to place on the back of the base.  If it isn't I may need to solder new buttons - but we'll see.

5)Something for IN the base - For my 20" I used a bluray drive hooked up to a computer by SATA to USB converter.  Bluray on a 17" monitor seems somewhat pointless (not that 20" is so much better).  I could do a standard DVD drive, Airport Base Station (thanks Roger), Large external hard drive? I know the ultimate goal would be a small itx computer or mac mini.  Unfortunately, I'm worried about heat issues with most mini-itx mobos.  Remember the base is not empty, it has the lcd controller, power source/inverter, and lots of extender wires which all take up significant space.  As far as the mac mini is concerned, it would likely have to be removed from its case.  Because the mac mini is so small, I'd hate to damage it for this mod when it could be easily hidden or displayed outside the base.  Plus, putting any computer in the base will eventually make it obsolete and require upgrading.  I have room for something the size of a 5.25" drive, if anyone has any ideas please let me know.

6) Griffin PowerWave Amp - For using the Apple ProSpeakers

7) Tools -
                 Torx set for taking apart the iMac
                 Soldering Iron and solder
                 Helping Hands (alligator clip soldering assistant)
                 Shrink Wrap (Highly recommend over electrical tape - these are tiny wires and if the tape comes off and two wires touch, at best you will loose signal, at worst you could fry your LCD screen)
                 Heat Gun (for shrink wrap)
                 Hot Glue Gun, Modeling Clay, or Silicon Gel to secure the extenders to the base

This list may change as the mod proceeds.  I will give specifics and images as I use materials.  But, if you have any questions just comment below and I'll do my best to answer.

II. Monitor 

The Hanns G Monitor arrived today and from external inspection, it appeared as advertised.  The keypad is reasonably sized and there is a DVI connection.  But, what is most important is what is inside.

First unscrew and remove the stand.  Then, using a flat head screwdriver pry the front bezel from the bottom.

With the back of the monitor exposed you can cut the aluminum tape with an X-acto knife.

Remove the inverter cables from the inverter using a needle nose pliers.  Of note, there are two inverter cables with both a high voltage (pink) and low voltage (white) line.  The inverter cable connects to the inverter via a 3 pin connector. (Only 2 pins are used and the center channel is empty).  Because my inverter extensions use a 2 pin connector I am likely going to have to change this cable to a 2 pin connector and re-use the three pin connector to connect to the board at the far end. 

We can now get a good look at the LVDS connector.  We can clearly see 16 wires arranged into pairs.  8 total pairs (Black/White. Brown/White, Red/White, Orange/White, Yellow/White, Green/White, Blue/White, Purple/White).  These paired wires use LVDS (small differences in voltage between the pairs) to transmit the image.

I have identified the 3 ground wires by white arrows.  These are the independent red, orange, green wires.

The three remaining wires at the lower portion of the picture designated by the black circle are the 12V wires.  These wires are black, brown, and yellow.

This makes for a total of 22 wires, significantly less than the 27 wires of the 20" mod.  Knowing  which wire carries what signal is important as we decide what wire we will use to extend this cable.

III. Cables
Options I am considering include the original iMac cables.  Shown here is the cable for the 15" iMac.  This cable includes 14 wires and 3 grounds of a slightly smaller gauge than the existing LVDS cables.  The 17 and 20" use a grey cable with 9 wires and a black cable with 4 wires which split into triplets (pairs + a ground).  The black cables wires are way to small and impossible to manipulate.  The grey cable appears to have wires of similar gauge to the 15" iMac.  The advantage to using existing iMac cables is that they come shielded and are already the proper length.  However, they are designed to carry a TMDS signal.  On inspection not all the wires are the same, some are smaller in gauge.  Because LVDS involves very small voltage differences between two pairs, I am concerned about the effect of using wires which may vary slightly in gauge and thus resistance.  Although I'm sure I could produce an image, if I choose poorly, it may be distorted.

After considering this, I am leaning towards using LVDS cables.  These can be purchased online.  I do not have cables long enough, but because I intend to splice them to the existing LCD connectors at both ends anyway, I am not concerned about lengthening them.  Using this method will leave me with unshielded cable, so I will have to use magnetic tape and heat shrink to shield the cable.  Because of the significantly fewer cables in the 17 vs 20" mods, I am not worried about the fit in the neck.  Right now, I feel as though I'd rather be confident in my connection, using LVDS cable to connect an LVDS signal and add my own shielding rather than using shielded TMDS cables which may have subtle differences between individual wires.  I may however reconsider this.

IV. LCD Controller

To completely free the LCD controller and inverter/power source, you need to unscrew the AC plug with a phillips head screw driver and use needle nose pliers to unscrew the bolts surrounding the VGA and DVI inputs

One of the "quirkier" aspects of this board is the fact that the controller and power source plug directly into each other via an 8 pin connector.  This can be seen in the center of the image.  To extend this I am going to use 2 4-pin USB extenders that end with 4 male pins.  These cables can be purchased at specialized computer stores such as frozencpu.  However, before I go any further and assume this will work, it should be tested.

Thats all for now.  The to do list includes:
       Test extended LCD controller/Inverter
       Determine LVDS vs. existing iMac TMDS cable
       Determine which cable will be used to extend touch screen
       If using LVDS, which shielding should be used
       Change inverter connectors (Change pins vs. cut and solder)

Once these issues are ironed out wiring through the neck can be done.
One of the unusual features of this board as I've mentioned is how the controller plugs directly into the power source/inverter.  Before we go any further its important to make sure that it is possible to extend this.  Using wire extenders (I have a 4 pin and a 5pin) there are 8 pins to extend.  So 1 wire is essentially unused.  Using these extenders, a clear image was produced.  So, one problem solved.

The second issue is the 3 pin cables that connect the backlights to the inverter.  Using a safety pin to release the pins, I attempted to switch the connectors from 3 pin to 2 pin.  Unfortunately, the pins on the monitor are too large to fit in the 2 pin connector.  There are two possible solutions, for one I could switch the LCD glass onto the backlights for the native iMac lcd.  The only concern I have with this id that I am not sure the backlights on my monitor work (I have a broken iMac G4 that has never turned on).  Before I can consider this, I'd have to test the backlights.
        Alternatively, I can simply cut and solder the backlight wires onto the proper connector.  Although this would be a permanent change, it should work just fine.

So, I've decided to use LVDS cables and add my own shielding.  As you can see there are more wires on my LVDS cable (right) than on the LVDS for the Hanns G Monitor (left).  That is fine as the extra wires are easily removed.  In this case I need 22 wires.  Although there are more cables, the basic layout of LVDS is the same.  You can see several paired wires and 3 wires on the left of the connectors that carry the 12V charge.  When buying LVDS cable online do not worry if there are more than 22 wires.  It does help to have an extra 30pin connector, but even if it is different, you can always use the connector that came with your monitor by either gently removing the pins and replacing them with the pins from longer lvds cables, or cutting and soldering the wires.  You need about 120mm of lvds cable to make it from the back of the monitor through the neck and into the base.  I personally do not have LVDS cables that long.  As a result ill be splicing 2 lvds cables (50+70mm) together.

LVDS cables are easy to extend if you take care to not cut the pins.  By placing the male and female pins together and adding a small amount of solder you'll have a solid connection.  I also highly recommend heat shrink (with a heat gun).  I find that electrical tape can easily fall off these small wires (especially with these wires that will be moving with the neck).  You do not want the exposed solder joints to touch (This could damage your LCD if the wrong wires touch).  Also, using a multimeter with a continuity mode can help verify your connection.

Now that I have my lengthened LVDS cable, the next step is to shield it and put it through the neck with the inverter extensions.  I will also have to decide how I want to lengthen the touch screen wires.  There will be a lot to do this week.

Taking a closer look at the LCD controller.  The Blue circle connects to the keypad.  The Green circle is the LVDS cable.  The black box on the lower right of the board is where the controller connects directly to the power source / inverter.  The board is 6mm x 9mm.  Note that this does not include connecting a DVI or VGA cable.

This is the power source /inverter.  These boards will be larger in AC powered monitors.  DC boards may have the power go directly to the LCD controller and have an external power brick.  This board has AC in at the green circle.  This gets converted to DC and outputs to the lcd controller at the blue circle. (You can see my extensions hooked up) The AC power also gets routed to the bottom of the image which are the inverter outputs.  These (red circles) are where the cables that connect to the backlights are placed.  These are 3 pin female connectors (although only 2 pins - 1 high voltage, 1 low voltage are used).  This board is 18mm x 12mm.  This board will fit into the iMac base without difficulty.
V. The Neck
This is the "new LVDS cable".  To make it easier to fit through the neck and the back of the iMac.  I divided it into 2 parts (similar to the silver and black cables in the native LVDS wire).  I added shielding with aluminum tape followed by heat shrink.  I did this both to protect the wire and also to prevent interference from the neighboring high voltage inverter cable that will be running through the neck alongside it.  Unfortunately, completely not following my own recommendations, I started adding shielding before remembering to label my wires.  So, I'll have to spend some time with the multimeter to verify my wires.
This 4 pin extension cable (the same exact cable I'm using to extend the LCD controller to power source connections).worked successfully with the touch screen and is long enough to go through the neck without any further extension.

I simply had to gently remove the bottom pins to allow for passage through the neck, then put the connector back once the pins are through.

I have previously detailed how to open the neck on this blog, so if you need help with that just scroll back several pages. I wired the inverter extensions in first (It takes 2 to make it through the neck, so I connected them in the center).  These are the pink and white wires.  I am not going to lie, it can be tough to get the wires through and if you knock the spring off its mount, it can be difficult to get the spring back on.  But, it can be done.  Finally I wired the touch screen cable through.  Unfortunately these small, thin wires barely fit as is.  I was unable to add shielding to this cable as I had hoped, with the other cables shielded I don't expect this to be a problem, but we'll see.


Above is the top of the neck.  You can see 2 inverter extensions with red arrows, 2 LVDS extension cables labeled with green arrows ,and 1 touch screen extension cable shown with a blue arrow.  The 2 LVDS cables join to one 30 pin connector that will plug into the monitor.  You will notice two "bulges" in these connections.  This is where I extended the cable, because the inverter cables will be away from the cable at this point I'm not worried about interference.  Also, because the wire is thicker here, I wanted to be able to flatten these wires out as it is a very tight fit in the monitor casing.

Below is the bottom of the Neck, you again see the cables labeled in the same manner.  The bottom cables will need to be soldered to the Hanns G monitors lvds cable and then the extension will be complete.  As I commented before, I will need to use a continuity test to determine which wire is which (Always label your wires).  

To Do List for this week:
- Continuity test / Wire Labeling
- Solder final part of LVDS cable
- Decide on which method to use to connect 3 pin inverter connector to 2 pin extender
- Test the Neck Wires

If the test is successful, I intend to begin assembling the mods base/monitor by next week.
As I had previously mentioned, I had forgot to label the wires, so I had to spend some time with a multimeter to figure out which wire is which.  The system I use is letters as you can see here.  However, by forgetting to label the wires and having to use a continuity test I located a small problem and was able to repair it.

I was actually short 3 70cm cables so for 3 cables I spliced two shorter cables together.  It appears when I was pulling the wires through I snapped the pin off one of these splices.  Although it was a pain to reopen the neck and fix the broken connection, I had known where the splice was, cut through a small section of shielding, stripped and soldered the wires back together.  Yes, I would have located the problem eventually anyway.  But, plugging it in and not have it working - would have been a great disappointment.  So new advice, label your wires, but no matter how good you think your soldering skills are - get a multimeter and do a continuity test.

So with the wires labeled, its time to splice them to the Hanns G monitor's short LVDS cable.  Just to be safe I only remove the wires from the connector as I solder, so there is no confusion as to which wire goes where.  To remove the pins, use a safety pin to lift up the small tabs.  If you're gentle, you can actually save the connector for use on another project.

So 22 more connections soldered and heat shrinked and we should now have a fully lengthened LVDS cable that is compatible with this monitor.

The next problem is the 3 pin inverter cables, while my extensions are 2 pins.  I hate permanently damaging things, that's why I like to use connectors when possible.  My options are changing the LCD glass onto different backlights (such as the native iMac G4's) or cutting and soldering (the pins are different and can't be swapped).  Because changing the glass can result in damaging the LCD and I feel as though I'm already "in too deep" to worry about salvaging this LCD for another purpose I am going to cut the inverter wires from the back of the monitor and replace them with wires that have a 2 pin connector.  Plus, I don't even know if the backlights on the iMac G4 LCD that I have work as the machine was purchased broken.

So, I am leading towards cutting and soldering.  But, before I cut the inverter cables it appears it is time to test the LVDS cable.  This is the part I'm most worried about because I feel I have already demonstrated that the inverter extensions work in the 20" mod.  So next the big test.....
I have never been so happy to see the target website.  As you can see in the picture, I am testing only the LVDS cable. The controller and power source/inverter are now plugged into each other, seen at the green circle.  Although I have previously demonstrated that they can be extended, I wanted as few variables as possible.  This does not test the inverter extension (or any interference these cables may produce).  Because the 17" has only two backlights compared to the 6 on the 20", I am very confident that they will work.  So, the native inverter cables are hooked into the inverter as seen in the blue circles.  The monitor is hooked up to AC power and a laptop via VGA denoted by the yellow circles.  The LVDS signaling runs through the neck (red circle).

Please let me give one word of caution - although it may seem obvious.  The reason I altered my 20" iMac mod with the touch screen and shelf on back was that I burnt out the power source.  I was creating a more permanent shelf and simplifying the wiring.  I was tired and being careless.  Before I was about to reattach the components to the back of the monitor, I wanted to test them to make sure everything still worked.  I placed the components on my table and hooked them up.  I didn't even realize that the edge of the power source was sitting on top of a sheet of metal.  One loud pop later I had ruined my mod.  So just remember to make sure you test on top of a non-conductive surface and that all conductive surfaces are clear.

So lets cut and solder those backlights, then its on to screen test #2.  After that I'll add the power source/inverter to lcd controller extenders back and then test the touch screen.  But all in all, I couldn't be happier so far.

VI. Inverter

To lengthen the inverter, I've chosen to cut and solder.  I have these short inverter cables (I bought them on ebay for about $3).  They are replacements for a macbook pro.  I will use these along with the cables that come off the monitor and connect to the 3 pin inverter connector to create adapters.  The reason I am doing this instead of cutting the wires I have going through the neck is because I want to preserve the neck as is.  I still have the option of changing the lcd glass to a different backlight and I have no interest in reopening up the neck if I screw things up.

I simply cut this cable in half and soldered it onto the existing backlight cable on the back of the monitor.  I used shrink wrap, but I will also reinforce this with electrical tape.

I then soldered the 3 pin connector wire from the Hanns G monitor to the remaining female half of my "macbook inverter cable" to create a 2 pin to 3 pin adapter cable.  Now let's test it.

Test #2 looks great!!!

You can see now that the inverter cables (red circles) go through the neck with the LVDS cable (green circle).  I still have to test this with the Inverter/power source to lcd controller extension.

 So here is the full test:

I placed the notebook there to simply hold down the extension wires that were getting in the way.  The extensions are connected (purple circles).  All wires remain going through the neck (inverter - red circles and LVDS - green circle).  I know the picture isn't great, but the image is perfect.  There is no distortion and the backlights appear to be nice and bright despite the additional length.

The only thing I do have to test is the touch screen extension, this I will do separately.  Other than that I am extremely happy with how everything is going and can fully endorse purchasing this monitor for the purposes of this mod.  It remains possible that I will still have to switch the LCD glass if there is a problem with either weight or fit.

The next step is to assemble the base.  I am actually leaning towards either an optical drive or nothing except for the monitor components in the base for now.  I want to be careful about putting too much in the base.  I am confident that I can fit the monitor components and keep them well protected and cool as long as I don't get overzealous.  I have purchased all my extenders and am going to try to make this mod look as professional as possible.

VII. Base
So after a long time taking things apart, its finally time to put something back together.  By dividing the LVDS cable in to two parts, it easily fit into the grooves on the base's attachment.

I stripped the base entirely to maximize the room available for the monitor components.

Because it is the shortest cable, the first component to be installed is the touch screen controller.

I secured all the connections with electrical tape.  Because the controller is so small and light, one screw is all you need.

The next component is the lcd controller.  Before I installed it, I secured it to my VGA and DVI extender.  These are simply male to female connectors that will allow me to make "ports" on the back.  Securing these to the back will also ensure that there is no accidental pulling of the internal components if one of the external wires gets caught on something.  This will also improve the aesthetic look of the monitor

Secure this in the base with a couple screws and its on to the inverter/power source.  After lots of contemplation I decided against putting anything additional in the base for now.  An optical drive will fit by placing the power source/inverter above it, but similar to my 20" mod, it will make things VERY tight.  The other thing to note is that this particular power source has somewhat of a funny shape to it as a result of the direct connection it has to the lcd controller.  It is actually longer than the power source for the 20" monitor.  The other factor is that I am not making this an all-in-one, so it will be connected to an external computer.  Both a mac mini and most laptops have optical drives, so this one would really be superfluous.  On the 20" I thought blu-ray was a worthwhile add on, but its hard to justify on a 17" screen.  So, I may add one later, but for now, I am not going to add any additional components.

So the power source.   To make sure there is no aberrant conduction, I dremeled a quick acrylic housing (seen in yellow).  Screwed on the power source and then mounted them both int the base, leaving room for the wires comping from above (the touch controller and DVI/VGA extenders).  I also connected the two 4-pin extenders to lengthen the connection between the controller and power source/inverter.

VIII. LCD Housing

Putting together the monitor is fairly straight forward.  It is important to secure the cables to the back of the monitor and make them as "flat" as possible.  It is a very tight fit.

While the monitor itself is about the same size and weight as the native iMac G4's monitor, there are some differences.  The LVDS cable is in a slightly different location and there are no grooves for 4 plastic pieces that are on the front bezel's grey border.  You can either switch the entire LCD glass to the native iMac's backlights or you can simply dremel these 4 pieces off, I chose the latter.  Although these screw into the monitor and ensure a snug fit, as I am adding the touch screen in front of the monitor, I did not want a very tight fit.

I added some clear mounting tape to secure the touch screen to the front of the monitor and placed it into the front bezel and monitor casing.  I then closed it up.

I added a short 3 flat pronged power cord extender, attached the keypad to the back panel so I could access the buttons.  Eventually I will alter the iMac and secure these to make easy to connect to ports on the back of the iMac.  However, for now I just ran them out the holes in the back because its time to finally see if this mod works.

See The iMac G4 17" TMDS to LVDS Conversion - Completed for Fully Assembled and Working Pics