Mod G4 iMac with Intel Mac mini innards?

Discussion in 'PowerPC Macs' started by casesensitive, Aug 14, 2006.

  1. MisterDNA macrumors newbie

    Feb 11, 2009
    That's a killer machine. It would look even more killer with a pair of iMac G4s as displays.

    I'll pull my inverter this weekend and head to work off the clock to see if I can get a partial schematic figured out under X-ray. I might not even need the X-ray as much if I can find datasheets for the components on the inverter board. The larger SOIC has me the most curious. I can't quite read the numbers on it in that picture at the other forum you posted the link to.

    I did find another supplier for inverter boards and one could be had for $26 in six-tube form, but it requires modification of the tube connectors to accept the doubled-up ones. Also, I don't think it's adjustable.

    Worth mentioning: The panel has a little more strict standards for power input than what's considered spec for an ATX power supply. While ATX allows +-10% on the 12V rail, the panel's Vcc of 12VDC is only rated for +-5%. The supply inside the iMac should of course operate within this range and, according to the USB 2.0 iMac G4 service manual, the supply is live on at least the 12VDC rail as long as it is plugged into the AC main.

    It might be better to use the iMac's PSU to run the panel. In my case, I will be putting a USB optical drive and eSATA-connected hard disk (or two?) and powered USB hub in the gutted iMac. All of these will surely run from the stock PSU with better lifetime on the PSU for lack of the logic board. After removing the guts from my own G4, it's dangerously top-heavy when the neck is all the way out and down. If you aren't going to put drives inside yours, weight them with a sandbag or something.
  2. newspimp macrumors newbie

    Feb 18, 2008
    The numbers on the largest IC chip on the inverter board I have is as follows... It's the one right next to the five horizontally mounted and sealed caps, numbered U2.

  3. MisterDNA macrumors newbie

    Feb 11, 2009
    Found a cousin! O2Micro makes the OZ971 and it would seem that the OZ964 is basically the same thing, but newer and in single form as opposed to dual. I will still have to do some X-ray work to make sure, but this gives us a lot of new info.

    The parts in the old family from which the OZ971S comes includes: OZ960, OZ961, OZ970, OZ971 and OZ963. I haven't been able to find datasheets on any of those.

    * Supports wide-range voltage input applications
    * Built-in intelligence to manage ignition and normal operation of CCFLs
    * 85% efficiency vs. typical 70% efficiency of conventional designs
    * Internal open-lamp and over-voltage protections
    * OZ960/961: Integrated burst mode control, and wide dimming range (10% to 100%)
    * Simple and reliable 2-winding transformer design
    * Supports multiple CCFL lamps
    * Constant-frequency design eliminates interference with LCDs
    * Low stand-by power
    * Packages available:
    o OZ960: 20 SSOP and 20 DIP
    o OZ961: 20 SSOP
    o OZ970: 16 SOP
    o OZ971: 28 SSOP

    It looks to me like the dimmer circuit will have to be set up for a minimum of 20-25% brightness to protect the tube electrodes if the circuit isn't already set up that way.

    It appears that there are supposed to be two supplies feeding the inverter. There's the supply voltage for the transformer inputs (~12VDC) and a lower voltage supply for the chip itself. It's possible that the purple 3.3VDC purple lead is this supply, but it could also be an enable line. Either way, this all revolves around the Yellow, Purple and orange lines.

    Judging by the reference circuit I saw in the cousin part's datasheet, it looks to me that the brightness is determined by a voltage between .6VDC and 2.1VDC with respect to the DC ground of the inverter board.

    There are variable DC power supplies at work that can be used for this investigation. I can even limit the current to prevent damage if I get the connections wrong even after X-ray inspection.
  4. WebmastuhB macrumors newbie

    Feb 18, 2009
    Awesome thread!

    Awesome thread...

    Phunker - I can probably get you a power supply if you need one. I can probably get a few. I am not sure if they work, but they should. I guess PM me...

    And to the rest of everyone on this thread - good work guys!

    I'd love to use the existing LCD on the iMac G4, and replace the motherboard with some kind of kick ass intel board (so I can get the latest software.) I was hoping there was a dongle or a connector or something that would allow me to hook the existing display with a newer motherboard (or a DVI connector, or a VGA connector, or something...)

    Any progress being made on being able to use the existing display?

    Anything I can do to help?
  5. MisterDNA macrumors newbie

    Feb 11, 2009
    The panels I have seen so far use a DVI-compliant TMDS signal. The plug and play features are not enabled through the iMac's display data connector, but they are present at the panel.

    The backlight has not been figured out yet. I will be doing that this weekend with the x-ray machine at work if I get the chance. I will also be hacking an old controller board into a suitable adapter to attach to a cut up DVI cable.

    All I need is time.

    In the name of making our mods look good, someone needs to find a way to thread a three-conductor wire down the iMac G4 arm so the DDC/EDID wires are available in the DVI implementation. If we don't have those wires and the data they carry, OSX users may be out of luck unless there's a way to manually configure a display with one mode and only one mode available like you can with Windows. Since I'm not hooking mine to a Mac or Hackintosh, I won't be exploring the nuances of OSX.

    If there is anyone who can get readings for the unknown inverter leads before I do the X-rays (which aren't going to answer everything immediately by themselves), I say do it.

    There is another possibility: Although my iMac wouldn't work at all while at room temperature, it would start up and even run for an hour or two with that powerfractal program while extremely cold out in my shop. If I can solder a piece of 8-conductor CAT-5 to the logic board for sniffer wires, thread them through the optical drive slot and take readings while messing with the brightness, I should have all of the data we need regarding the inverter.

    Actually, I can probably scrounge up at least three multimeters and a dual-trace oscilloscope to see everything at a glance.
  6. WebmastuhB macrumors newbie

    Feb 18, 2009
    Cool Stuff! Well good luck...

    I wouldn't mind building a hackintosh out of this. I imagine a small form factor intel based mother board could be purchased cheaply, perhaps it has a DVI port on it, and this monitor cable could just be hooked to that.

    I'm more of a software guy and less of a hardware guy.

    Interesting stuff, but I am a little lost. I'm not into the nitty-gritty of hardware. Sorry.

    But SWEET! Keep me posted, this is pretty interesting.
  7. newspimp macrumors newbie

    Feb 18, 2008
    It may bot be present or wired up in the 15" model, which was pre-official DVI spec, but the 20" cable does have the three wires for DDC/EDID. Pins 17,19 and 20 IIRC.

    So, we may be able to pipe the DDC/EDID through those wires since they're already present and at least on my 20" hooked up to the proper inputs on the LCD controller board.

    Gotta love travelling for work. Catching up on about 200 e-mails today!
  8. MisterDNA macrumors newbie

    Feb 11, 2009
    I put the iMac back together and I'm chilling it down outside in my shop. Since it's supposed to get down in the teens overnight here, I should be able to find out whether the inverter will run.

    Okay, the iMac didn't start up after being chilled way down. I will have to go about this the hard way and I didn't have time for that this past weekend.
  9. newspimp macrumors newbie

    Feb 18, 2008
    I have a 20" iMac inverter I can send you to try out if needed. I'm not 100% on whether it's working properly, though. Also, may be useful in determining if they used different ones for the different panels.
  10. harry454 macrumors 6502

    Sep 13, 2007
    yeah someone should try it out and see if it works, if you do post a picture!
  11. MisterDNA macrumors newbie

    Feb 11, 2009
    I am in my workshop right now, pulling the iMac G4 apart for the run at reverse-engineering. I have it all torn down and the wrapping taken off of the inverter board. The board is two-layer so I may not actually need to use the X-ray machine unless there's some thing hidden under the OZ971S controller IC. Since we should have an outline of where pins connect to start with, I will put some info here.

    1,2: Vcc 12VDC
    3,4: GND
    5: Connects to R2 (which measures 10Kohms), which is in series with R3, a 47Kohm resistor the other side of which is connected to a fat trace with one side of C10 to Pin 28 of the OZ971S controller IC. This is going to be important for sure, but it's supposedly not connected according to research newspimp posted.
    6: Connects to R5, which I can't read, but get a reading of 4Kohms off of, through which we are directly connected to Pin 3 of the LM393M IC, C16 to GND, R8 (which is .5Mohm and connects to the GND through C17)
    7: Connects to the positive side of D3, through which we connect to the collector of Q7, also branching out through a 10Kohm resistor to Pin 28 (GND) of the OZ971S and Pin 1 (Silkscreen says 1 while datasheet for part says Pin 2) of Q5 (which is etched "1AM" on top, making it a 3904. The silkscreened Pin 2 of this part is connected to the negative side of the ZD4 Zener Diode
    8: Connects to the Bases of Q1 and Q2, but also through a 1Mohm resistor to the system ground. You'll like this: The collectors of Q1 and Q2 (controlled by Pin 8) go through 30Kohm resistors to the collectors of what look to be transistors on a circuit bank that monitors the low side of each lamp.

    The high side of the lamps appears to be monitored through pin 11 of the OZ971S IC.

    Pins 5,6 and 7 on the comparator aren't being used, meaning that on a dual comparator IC, there's only one comparator being utilized. I recall comparators being part of how the inverter controller does its thing regarding brightness.

    Pin 6 of the OZ971S is connected to Pin 8 of the comparator, making that the supply for the comparator chip.

    This is very rough and I'm posting it as I write it.

    Inverter pins from the motherboard:

    Between purple and yellow: Resistance = 20Kohms
    Between orange and yellow: Positive on yellow, negative on orange: 1.7Mohms, out of range the other way
    Between Orange and Purple: Positive on Purple, negative on orange: 1.7Mohms, out of range the other way

    Tested as diode rather than resistor, I see voltage drops of 1.414VDC with the leads arranged the 1.7Mohm way and 1.46 the out of range way.

    DDC/EDID functionality confirmed on iMac G4 20" display panel!

    Pin on motherboard connector and where it goes:

    Pin 17: V-EDID (Pin 15 on bare LCD module)
    Pin 19: Clk-EDID (Pin 17 on bare LCD module)
    Pin 20: Data-EDID (Pin 18 on bare LCD module)

    Look here:

    This could be really interesting. It's the same user whose inverter pinout we've been referring to. It would seem that the inverter blew an inductor and wouldn't fire up so that would explain why nothing ever reached a solid conclusion in that thread. This user fitted the display with a generic inverter and found that while the iMac uses a voltage of between .88VDC and 3.3VDC for brightness level, the generic inverter used 0-5VDC.

    I signed up for the apple forum and posted there. The whole thing has played out over a couple of weeks so it should be possible to get new data if I don't figure it out before he replies.
  12. MisterDNA macrumors newbie

    Feb 11, 2009
    I've figured out a circuit for the dimmer. It's based on a potentiometer and the working voltage range of between .9VDC and 3.3VDC with 3.3VDC being max brightness. The 0.9VDC is a hard minimum and must never go below that so I'm going with a safety.

    From a 5VDC rail:

    R1 = 470 ohms 1% tolerance
    Output at the end of that.
    R2 = 0-1K potentiometer (a really good one)
    R3 = 110 ohm 1% tolerance (may need to use 100ohm and 10ohm)
    Ground after R3

    I really wish there were something more elegant than this within easy reach. I don't like analog controls and I suppose I could use a resistor ladder of four bits or something like that off of a microcontroller. It would be cool to have that as one feature of a secondary system driven by the microcontroller and including an LCD display for system data and other functions.

    An ATMEGA128 would work very well for such an application, but so would a Parallax Propeller and I don't know those yet.
  13. tjka4321 macrumors newbie

    Mar 12, 2009
    mini-itx motherboard + add2 graphic card with "TMDS output"

    I just wonder if it is possible to put a mini-itx motherboard to make a PC into imac G4 dome and use an add2 graphic card with "TMDS output" to utilize the imac's flat panel.

    My imac G4 17" is just running its screen saver everyday. What a waste!

    TIA for any suggestion/advice.
  14. newspimp macrumors newbie

    Feb 18, 2008

    Nope. At least not as you've said it. One thing that we've definitively come to is that the video input for the iMac LCD is *NOT* TMDS. The iMac G5 and subsequent Intel models is TMDS, but for all but final testing, the iMac G4 video input appears to be PanelLink for early 15/17" models and full-blown DVI for later models.
  15. MisterDNA macrumors newbie

    Feb 11, 2009
    I believe you are confused, newspimp. DVI and TMDS are the same thing. If you were to replace TMDS in your post with LVDS, you'd be right.

    Fact: TMDS is a form of LVDS signalling. LVDS stands for Low-Voltage Differential Signalling. TMDS stands for Transition Minimized Differential Signalling. Both are low-voltage.

    Transition minimization is a kind of protocol used to reduce the radio frequency of the signal on the lines to allow higher resolutions and longer line lengths. I could go into how it works, but anyone can look that up and it's easier to say why they do it.

    They are not, however, directly compatible. There are GPUs with switchable modes. That's a build-to-order thing and changing the wiring to convert to the other means messing with the GPU at the ball-grid level if you can even find a datasheet for the GPU in question and then writing your own firmware since you aren't likely to get significant help from the GPU vendor.

    I haven't worked on the iMac project for a while. I'm stuck waiting to find a good DVI breakout or a video card I'm willing to sacrifice to the cause.
  16. newspimp macrumors newbie

    Feb 18, 2008
    Completely right... Had TMDS on the mind. What kind of DVI video care are you looking for? I have quite a few in spares right now...
  17. djuro macrumors newbie

    Mar 26, 2009
    Different approach

    Ok, guys, how about if we change approach? I was thinking of upgrading the screen as well. Samsung is producing LCD panel 15" (4:3 aspect ratio, check link ) which should fit in nicely. Now, my thinking was: if we do know what kind of display we do have, and we can get documentation for it (I have found it on 'net) is it too much hassle to produce electronics that would convert it defacto to monitor. That way we could just plug it in to DVI output of mini and we have solved 85% of our problems? After all, this LCD panel has 1400x1050 pixel resolution which would make a nice hike comparing to original 1024x768? The price is also OK, not too steep and the Lamp would become modern computer in EVERY respect?
    Now, I have a degree in engineering so I can contribute when it comes to packaging, but this electronic stuff is beyond me.
    Perhaps MisterDNA could do something about it?
  18. newspimp macrumors newbie

    Feb 18, 2008
    Well, the good thing, should that tack be taken, is that the mapping of the existing wiring and all of that really isn't as needed.

    What we've been looking at is mapping out the inputs for the existing LCD panels and it's inverter and converting that to DVI.

    If you replace the panel and the inverter, then that's really kind of out the window. If you can strip the casing off of the LCD monitor that you're looking at, and make it fit within the iMac case, the running the standard size power and DVI through the arm should be a minimal problem. You'll certainly have to cut the ends and resolder, or work up a disconnectable end that will fit through the narrow iMac arm hole, but that shouldn't be too big of an issue.
  19. mhfdejogn macrumors newbie

    Apr 21, 2009
    Whoow this stuff just blows my mind:| I've had the same idea for the last couple of weeks now. I have a 20" imac g4 on my desk at the moment, and I love it, but I would like it to have a little more power in it.
    I've read through the entire threat and in seems like there is a big problem with the way the display receives it's data and power. I have absolutely NO clue how to tackle this problem, but I would like to build my mac mini in the g4 case. It seems that the only way to do this is to also replace the screen.
    I hope you guys can find a way to make a converter of some sorts and make the entire process of assembly easy enough for me to be able to reproduce.
  20. SkippyThorson macrumors 68000


    Jul 22, 2007
    Utica, NY
    I just had an idea. Obviously the iMac Screen would be too difficult to connect to the board of a Mini, but what if these were closer in technological build?

    My idea is this: what if the solution lies in not connecting old screen to new computer, but connecting new screen to new computer in old case.

    A 20 inch iMac and Mac Mini of the same time would have a lot of the same components, right? So is it at all possible to for the new 20 inch screen with the new connectors to fit in the casing? If so, a closer set of components may be part of the answer.
  21. Clive At Five macrumors 65816

    Clive At Five

    May 26, 2004
    St. Paul, MN
    Wow, this is incredible. I've been following this thread off and on for about two years, hoping for a way to breathe new life into my original 15" 800Mhz G4 iMac. I have to confess that most of the hard-hitting stuff has gone a bit over my head, but if there's any way that a mere mortal with a modest knowledge of circuitry can help, please let me know! My iMac is OPERATIONAL and in perfect condition, except for the fact that it's slower than hell. :D

  22. newspimp macrumors newbie

    Feb 18, 2008
    Well, the biggest problem with using an iMac G5 or iMac Intel LCD screen is that they use LVDS connections to the LCD panel from the motherboard. This is most commonly used in laptops.

    The big reason that the G4 iMac is promising is that it uses TMDS signalling and appears to be DVI compliant going in. That much I think we're fairly certain on. The biggest step right now is getting the inputs for the LCD panel inverter going.

    LVDS monitors have this problem as well, but the biggest problem is that they need an LVDS to VGA or LVDS to DVI converter. Generally, these are pretty expensive and you still have the backlighting control to contend with.

    Once the wiring is done for the DVI connection, and a suitable controller for the backlight is developed, then the iMac G4 LCD panel becomes a standard DVI monitor, and is connectible to anything. That is the ultimate goal for me.

    I've just changed jobs (going from Mac Pro to unibody MacBook Pro sucks), and now have a lot more access to electrical engineers and circuit guys! Hopefully we can move forward on this soon here. Once I'm done moving to the new house, I'll have room and time to dedicate to this project. My electrical tools and spare panels and inverters have been packed for a month now...
  23. MisterDNA macrumors newbie

    Feb 11, 2009
    I should mention that I haven't left or forgotten this project. I've just been too busy and then too sick to do anything with it, but I have my jerry-rig DVI cable and it's all down to electrical now.

    I won't be able to continue my work until the end of the month as I get knocked out for surgery on the 12th and then, if I survive, will be down for about two weeks.

    With the recent refresh of the Mac Mini, this is even more intriguing to me.
  24. billib macrumors member


    Apr 23, 2009
    My iMac 2¢

    I'm not an Mac expert so please forgive me!
    Wouldn't it be easier/cheaper to buy an inexpensive LCD monitor from NewEgg or TigerDirect, then remove the LCD panel from the monitor along with any electronics? Swap out the iMac display and components and connect the new VGA/DVI (?) cable the Mac mini you've hidden inside of the iMac base or connect it to an external Mac. Wouldn't this be quicker/easier to do than risk getting the pin out wrong on a hack of the original components and frying something? Also the LCD spec's are not great and the resolution is a tiny bit on the low side on the iMac. A new inexpensive LCD monitor can easily better it.
    I have a 20" iMac and a hacked Mac mini with a 2.33 GHz Core2Duo Processor so I would like to blend the two eventually. I must say I'm not sweating the LCD hack but I am stumped on making a DVD w/tray work with the mini when its shoehorned into its new home. How will they fit? How will they connect? How will they work together?
    I think the LCD hack will be (relatively) easy. Its the DVD that will be hard. NO?
    Check out my Mac mini hack:

Share This Page