Monday, February 20, 2012

iMac G4 Mod Advice

I hope this doesn't come across as preachy, but I just want to give some advice to those of you new to modding the iMac G4.  I have disassembled and reassembled this computer so many times I could probably do it blindfolded.  There are a few aspects of modding this computer that have led to a lot of frustration for me, a few pointers, hopefully, will help some of you.

1) If your goal is to connect your iMac G4's LCD to modern hardware.  Use the Native LCD with the "TMDS to DVI Method".  Changing all the wires to some other method of connection such as LVDS is very time consuming, less stable, and more expensive.  There is no reason not to use the native TMDS wires that go from the native LCD through the neck.  Apple has already done the work for you! Plus, TMDS is a digital signal that is more stable over distance than LVDS and TTL.  Apple has put the controller inside the LCD itself, with other LCDs, you would have to add one.  I have done this both ways, replacing the screen and replacing/soldering the wires takes hours and likely days.  By using the TMDS to DVI Method with the DVI Connector below, you could get a signal within 30 minutes that is superior in every way.  Which brings me to.....
DVI Connector


2) USE THIS DVI CONNECTOR!!!  (MOLEX PN 74320-4004 - though other variations which work just as well exist).  It is very cheap and makes this mod so much easier.  I can not emphasize this enough. I know a male HDMI may be more convenient (or even a male DVI), but for the price of an adapter you will save yourself a lot of frustration.  Sure you could cut off an HDMI cable and solder it to the iMac G4's pins, but this is a much harder task than you may think.  The TMDS channel wires in the Black LCD cable are as thin as a hair and this is no exaggeration.  If you manage to spare the pins at the end of the wires during soldering this can be done.  But, as the pins are soldered to the ends of the wires themselves, they have an annoying habit of falling off when heat from a soldering iron is applied.  Also, if you make a mistake while soldering there is no going back.  As this is a digital signal, one broken connection can mean no signal at all.  What's more is that even if you do things perfectly, you can still have signal problems.  One mod that I made I had to cut and reconnect again (so I lost all the pins).  Despite a perfect connection, the image was plagued by artifact.  Another time, I had red/green pixels "dancing around" when viewing certain colors.  I ended up having to replace the entire Black LCD cable (with the TMDS signaling cable from an Apple Cinema Display which has thicker wires) to solve the problem.  TMDS uses minute differences between the positive and negative wires (and their shield wire) to communicate.  Altered resistance in the form of a little too much solder or too much wire wrapped around can result in these types of artifacts even if you are extremely good with soldering.  This DVI connector makes this almost plug and play.  The pins fit perfectly,  you don't need to solder at all.  I am not exaggerating when I say that this method saved me 10+ hours of intensive work on my recent mod.  Besides having to put a piece or two of electrical tape over some pins to prevent cross-talk, my image has been pristine every time I have used this connector.  Do not repeat the same mistakes that I have made.

iMac G4 Neck with Cinema Display Wires
3) Although no longer necessary with the TMDS to DVI Mod, if you want to add or change some wires, do not be scared to open the neck.  Its not hard, does not require special tools, and is not really dangerous.  I have written on this blog about the exploding neck because I had read about it myself.  I've had an open neck fall off the table, I've left necks open for weeks at a time, and have never had the spring fly off.  I wouldn't throw an open neck as hard of you can against the wall, but you do not have to handle it like its plutonium.  Just keep in mind that  if you do knock the spring off its moorings it takes a lot of work to pry it back up into position.

4) If you need to add wires to the neck, do not put more/thicker wires into the neck than it can hold.  Just because you can get it through the holes does not make it a good idea.  When you overcrowd the neck, you'll start to hear grinding and some wires will wear down as they are pushed into the hinges of the neck.  The iMac G4 has 4 wires that go through the native neck.  When you replace wires, take out what you're not using and aim to have about the same "volume of wires" as the native neck comes with.

5) Get rid of the Torx-6 screws.  These are the most troublesome screws I have ever worked with.  On the bottom of the 17" and 20" iMac G4's monitor housing you will find 3 screws that require a Torx-6  screwdriver to open.  These are the screws that keep the monitor housing closed.  I have never seen screws that strip easier despite using the appropriate tool.  6 points on a tiny screw is very close to a circle and once you start stripping it - its already too late.  Chances are good that you may have to open up the monitor housing again at some point for upgrades, repairs etc.  Act preemptively and replace these with small phillips screws - it will save problems later.

5) Want an All-In-One? Consider an 3.5" ECX or other small form factor board.  Although mini-itx or a mac mini motherboard are the most popular choices neither of these is ideal from a size/heat perspective.  ECX's can fit at the top of the dome in place of the native HDD where heat won't be as big a problem as it would with a mini itx at the bottom of the dome.  They don't require an atx power supply and come with a variety of additional options including PCI-E mini or x4, Compact Flash etc.  Processors range from Atom to AMD Fusion to Sandy Bridge Core i processors.  This allows you to keep the full 5.25" drive if you want and allows room at the bottom of the dome for ports at the back.  Although not nearly as expandable as a mini-itx mobo, with such limited space in the dome, this isn't likely to matter.

6) Do not sacrifice stability for power.  The mods I've posted usually don't include the mods which failed.  Most of these initially worked but failed because I tried to force things.  If you have to use all your strength to push your mod closed to screw it in, it will not last.  If you cram things in between the motherboard and the air holes, your board will overheat.  Keep expectations in check.  If you have a 17" monitor running at 1440x900 you don't need SLI or Crossfire.  Having it turn on and having a critical problem like this is worse than it not working at all.  If it does not turn on, you can start troubleshooting what went wrong.  These problems (like my 20" TMDS to LVDS with too many wires through the neck) usually require a complete redesign and many of the parts have to be repurposed or replaced altogether.

Hope this helps.

32 comments:

  1. I really appreciate everything you have done. I am beginning to get the itch to mod out my old imac g4. I only have any idea because of what you have written.

    Thank you.

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  2. I've got an old imac G4 15" which I have been trying to mod, but I have given up many many years ago. I have hope.... although the wiring could be quite different than the 17"

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    1. Please see the 15" Pinot I posted courtesy of the modded pgee70

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  3. I have a question. I have opened up the iMac G4 to change the wires, but now the pivot at the bottom of the neck that connects to the dome has come out of its hole and I cannot get it to fut back in. It seems like it is too short, but that can't be possible because it just fit perfectly before it was opened. Do you know how I can fix this?

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    1. Its likely too short because when it came off the moorings the spring contracted. If you take a thick, solid flat head screwdriver you may be able to pry it back up into its hole by extending the spring

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    2. After I stick the screw driver in and pull extremely hard, the pivot is so very close to popping back into the mooring, but it doesn't. Do you know any tips? Is there somewhere I could take it to have them fix it? Or do I just have to buy another one?

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    3. I have also sent you an email with pictures of the problem, if you could also take a look at that please.

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    4. I know how infuriating it can be, but it is doable. If you get close start pushing it in as hard as you can. Start with one side and tilt the inner part and pry it up with the screwdriver. Once it even catches on by a nub, you should be able to press it into position.

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    5. Thank you so much!! I finally got it back up into it's slot. Sorry to ask of any more things, but now after I have the arm back together, the screen doesn't seem to stay in place. If I pull it to a certain level, it will pretty quickly snap back upright. Is there anyway I can fix this, or is it normal? Thanks! Sorry for asking so many questions.

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  4. Oops, I spoke too soon. Putting the LCD in the enclosure fixed the problem :P

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    1. No problem. As you can see the arm is designed for the LCDs weight

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  5. Absolutely excited about my first build, with an MITX board lying around and an iMac G4 15" (800 MHz model) I picked up for $40. End goal is an elegant little Minecraft client whose display can be easily angled down for my preschooler.

    Problem is, I gather the pins won't match perfectly as in the 17" instructions. Would you suggest (with no warranty implied, of course!) that I could use the DVI Connector (MOLEX PN 74320-4004) and Pgee70's DVI Pinout schematics?

    I'm just learning the PSU details and ordering final pieces for the project next week. Thanks again for sharing your brilliant experiments with all of us, inspiring something wonderful.

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    1. B Wesley - glad to hear that you are ready to go. 100% ABSOLUTELY USE THIS CONNECTOR. I can not emphasize this enough. The 15" uses the exact same TMDS signal that the 17" and 20" use. In fact the only difference between the 17" and 15" is that the LCD for the 17" requires 3 wires for power and 3 for ground, while the 15" has 2 power and 2 ground. So there are 2 extra wires for the 17", except for that you should be able to follow the general concepts behind the 17" (and for that matter the 20") when you do the 1" mod. The pins are the same size and obviously use the color chart to determine which wire is which that pgee has provided. But, using the connector takes away 90% of the labor of this mod. Not only that, but it makes it far more likely to have a interference free signal at the end. Preserve the pins carefully as noted in my mods and you will be fine. Good luck and thank you for the compliment. I am happy to help and am available to help if you run into any problems along the way.

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    2. 1. I originally intended for native iMac PSU to drive native LCD's inverter, but it looks like LCD power was instead controlled by the logic board. If I pick up a DC-DC 120w+ PicoPSU (likely this one http://goo.gl/bhevA)is there *any* reason to use native iMac PSU vs an external power brick (besides asthetics)?

      2. I'm planning to install an mITX Intel motherboard with 2.5" HDD into the iMac G4, powering them plus the native LCD from the PicoPSU (I estimate that the peak power profile, excluding LCD, shouldn't exceed 90watts).

      Any new/specific recommendations for a first-timer intending to wire power to the Native LCD via a standard 8981 Molex connector? The instructions are a bit daunting (hair-thin-wire soldering makes me nervous!) but I won't be dissuaded! I'll just be taking it slow.

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  6. I have a 17" sunflower G4 iMac that I'd like to convert into a DVI display, but am not sure how to tell if the panel uses TMDS or LVDS. How do you tell? Do all 17" G4 iMacs have TMDS panels? Do you have to open it up to find out or is there a way to tell from which model is it? Thanks!

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  7. Any thoughts on hacking a 2007 (aluminum Intel 20" or 24" iMac) into an external display? I have one of each of these machines, and they are starting to show their age in slower performance -- but they would still make a great display for a new Mini... Thanks!

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  8. These LCDs use LVDS instead of TMDS, so an LCD controller would have to be added. These can be special ordered through certain companies based on the particular specs of the panel and backlights

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  9. First off, amazing work. Your sandy bridge conversion is my ultimate goal for an iMac.

    I'm working on a little project right now, and I was wondering if you knew the approximate weight of the screen assembly so that I could replace it with something of similar weight to keep the functionality of the arm.

    Thanks
    Tyler

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    1. Tyler, I have the weights and dimensions in my notes somewhere, to make finding it easier, if you could, let me know if you are talking about the 17 or 20" iMac.

      Just a word of caution, just as important as overall weight is distribution of weight. Most Non-LED and even some LED monitors tend to have a "shelf" on the back for the components such as inverter/power source and the controller. This tends to place the monitor's center of gravity further in front of the neck (essentially a thicker monitor). This can cause problems with the lower hinge (moving the monitor up and down), but is especially a problem for the upper hinge (tilting).

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  10. Hey guys!, I was wondering if I can use an xbox 360 power brick to get the juice for my iMac mod. The thing is, that brick gives 203W, so at first, will you say that 203w will be enough to feed a core i7 3770s, 8gb of ram, 20" LCD panel and a mITX motherboard? If yes, do you think that I a pico PSU is absolutely needed, or will I be able to transform the 12v and 5v volts that are given by the brick into the 12v, 5v, and 3.3v needed by an ATX conector?

    I know some people has done this xbox 360 brick mod and they succeeded to get a clean 12v 203W power source to feed a pico PSU 160W, but then they are wasting some juice from the brick because they are not getting the total 203W because of the pico. What I want to do is to convert this brick into an ATX power source. I mean, it has 12v and 5v already, I only need to get somehow the 3.3v needed by the motherboard and then I will have the cheapest and easiest power source for this kind of mod. Pico PSU are a great solution but I'm looking forward to just use the xbox brick if I can.

    Thanks in advance for any help! And sorry for my bad english.

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    1. Juan, unfortunately I am not familiar with using the Xbox brick in this matter. Down converting either 12V or 5V to 3.3V will not be difficult. Similar to a pico ATX power supply any DC converter will have a certain wattage limit. But, this would apply only to what is downstream of the converted rail. Finding a downconverter should be easy with a google or eBay search.

      The LCD requires somewhere around 40 watts, so this leaves you with 160 watts. I plugged what you gave me into a PSU calculator and assumed 2 sticks of ddr3 ram, 1 ssd, 1 92mm fan, and use of 2 USB ports and the minimum recommended power supply was 150 watts. Again, this is an approximation - it looks like you may squeak by, but its close. Adding, wifi, Bluetooth, will add a few more watts as well. Again, no guarantees.

      Also remember you need 24V to power the 20" LCD. To be honest, the xbox360 power brick is an absolute monster, especially the original Xbox 360, which is the 200 watt one you are referring to. I would favor using the PSU from an iMac G4 (or even an iMac G5), the G4 being 190watts, and running a 12V rail through a 150-160 watt Pio PSU to downconvert. You will not waste any wattage as you can power the LCD via a separate 12V line and the backlight off the 24V line. Thus 40 watts will be used before the pico PSU.

      That said, if you are planning an iMac G4 mod, I do not like mini itx form factors for this. Heat will likely be as big or a bigger issue than power. But, obviously there is no "right" way to do this, it's up to you.

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  11. The reason I thought Xbox bricks are a good idea is because it is very difficult to find a functional iMac G4 20" PSU in my country. I started buying pieces from broken iMacs even from foreign countries, but non of them included a funcional PSU. My goal now is to convert that brick (that actually is a very cheap and powerful power source) into an external ATX power supply. I just have to downconvert 12v or 5v to 3.3v and upconvert 12v to 24v to power LCD. If I success in this, I will have a picoPSU free power system. I'm not against picoPSU but my truly goal is to achieve this mod with the less money possible. Buying that used brick only costs me like 20 dollars. Otherwise, if I have no success, then I will order a picoPSU that surely will take 1 month to arrive to my city.

    Considering the heat issues, I think that I will choose an ultra low power consume processor like Corei7 3770T or maybe a corei5 T-line. I really wanted to get an ECX board but the only one that is really in my budget is the Intel NUC, but unfortunately it has no USB 3.0 and just a Corei3. The other ones are very expensive and this is against my goal of making my mod a cheap one.

    If I succeed with the Xbox PSU to ATX PSU mod, I will let you know. Maybe it is helpful to people with a damaged PSU or maybe they want to use an external but powerful PSU without needing another PSU inside (pico).

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  12. Hello,

    Love your site and all the helpful tips. I tried the DVI mod and was actually quite successful. However, I didn't find it was all too reliable as an external monitor. I also didn't have a great way to manage the cabling. As such I decided to embark on the VESA mod instead.

    I bought a 21" LED monitor. I was hoping to mount it on a 20" Neck, but after taking the neck apart and taking out the cables, I'm having trouble putting it back together. The two halves don't line up flush, and moreover, the neck doesn't seem to articulate properly. Any suggestions for this?

    The bottom socket did get dislodged, but I can manage to get it seated back into the hole with a little effort and a screwdriver.

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    1. Unfortunately these can be very temperamental. Is there any chance one of the velvet or black plastic liners got dislodged or stuck anywhere. The other possibility is that there are simply too many wires. When you overload te neck they can grind against the spring attachments.

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  13. I have a question: If there are 2 tdms channels in the imac then could I patch in an external hdmi output to use a second monitor, or somehow use a second input to use the g4 as an external monitor for something else and switch between the G4 and external display mod on the fly? how does this dual channel tdmi thing work? or am I confusing that with the DVI standard that has 2 channels and the G4 imac only has one?

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    1. Sorry if this isn't clear. While there are 2 main cables which contain the DVI signal, there is still just one DVI signal. The term "channel" I use here to denote the color signal coded for by the wires. The grey wire contains "regulatory wires" such as power, ground, identification, on/off etc. The black wire contains "4 channels" of one DVI signal, these are 0,1,2,&Clock - these correspond to Red, Green, Blue, and Clock (refresh timing). Each one of these channels is actually composed of 3 (a triplet) set of smaller wires (positive, negative, and shield). However, it's still just one DVI signal. Could a KVM switch be wired in to support 2 inputs, sure, but it would be difficult to do without damaging the original connection to the G4s mainboard.

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  14. Dear JBerg,
    I`m stuck and confusing. I Purchased another Neck of iMac G4 17", I followed your video step by step. However, When I tried to hook up the three Blue, Yellow Orange cables from Gray cable, It was like very hot and some tiny smokes and sparkles came out.as the picture shows. Did I do something wrong about that? Can you fixed my problem? thanks and wait for your answer.
    https://lh6.googleusercontent.com/-nV2UgR7FS1I/Uc4wC0W0z-I/AAAAAAAAAC0/n7huLVSL5f0/w1075-h806-no/IMG_1835%255B1%255D.JPG
    I was trying to hook up those three cables to the red 5V molex cable as the pic shows.I couldn`t because it would burned.

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  15. I'm wondering if it's possible to use a higher resolution LCD panel from a laptop on an iMac G4.
    My situation is this: I have a 17" iMac that has a dead LCD. I have a 15" iMac that's fine, and I have the LCD from an old laptop that is 15", but a much higher resolution than the 1024x768. I remember reading somewhere that the 17" imac's video chip could understand TMDS as well as LVDS (but I can't find it now for the life of me). The connector for the laptop panel fits the same one for the 17", so in theory I could just swap the 15" bezel for the 17" and it should work (if I can work out something for the inverter, the 15" and 17" inverters use different plugs)

    So could that work or am I crazy?

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  16. Heya Buddy!!!


    LOVE, Love, love your stuff!!!

    I've got a (simple?) question that I HOPE you can answer.
    I LOVE my G4 & don't wanna say "goodbye" to it, BUT...
    the power button is trashed... gone... so I can't turn it on anymore.

    I saw a suggestion (somewhere) that a G3 keyboard (with a power switch)
    will turn it off & on.

    They're pretty cheap out there, will this work?


    Dean

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  17. Hi! Instead of using a DMI receptacle for the Imac G4 monitor, Would it be possible to use HDMI directly? I was thinking of using this part =

    http://www.molex.com/pdm_docs/sd/887645900_sd.pdf

    what do you think?

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  18. I have a 20" model which is in pretty nice shape, I'm not moddling it, I just want to fix it - but from the get go it always had problems starting from the power button. It was unreliable to start, but once running it was fine and reliable. Sometimes it took several presses before it jumped into life.

    I wonder if you could comment on where I would look to get the power supply working again?

    Because the power button responded normally once the computer was actually running, to put it to sleep or wake it up, I think there is no physical problem with the start button. If I set it to start at a certain time of day it would always boot on schedule. But now I can't get it to start from the power button at all.

    I think that the power supply works fine when running, but now it’s just silent and dead.

    I'm trying to understand how the power supply actually initiates the boot sequence, it seems quite complicated. I wonder if you have any pointers about where I should look to try and troubleshoot this? I've read your description of the native power supply. The pram battery is fine and I've tested that with a 500 ohm resistor across it to load it a bit and it's in good shape, about 3.6 V steady.

    I've had the iMac open several times as far as the fan, screen and the power supply and would appreciate it if you have any insight about my problem.

    Thanks, Leewave

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