A new iMac G4 Mod with up-to-date hardware and unchanged appearance including pro speakers

Discussion in 'iMac Mods' started by wingworm, Mar 1, 2014.

  1. wingworm

    wingworm

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    Mar 1, 2014 at 4:37 PM #1
    wingworm

    wingworm

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    Main features of this Mod:
    1. Built over industry standard platform(thin mini-itx), easy to upgrade with newest hardware
    2. Original working IOs (Ethernet, 3*USB2.0, 2*USB3.0 via original 1394 port) over unchanged appearance
    3. Native Pro Speakers support through original 2.5mm mini jack and class-d amplifier with no mod, plug and play
    4. Original internal speaker supported
    5. Jack detection enabled for original 3.5mm headphone jack and 2.5mm mini jack.
    6. Original power indicator LED and Microphone inside LCD panel
    7. Newest standard Wi-Fi and Bluetooth support with original antenna
    To be done:
    8. Digital audio interface by reusing original 4-pin telephone connector (+5V,digital out, digital in, GND)
    9. Mini displayport output by reusing the mini VGA port
     
  2. wingworm

    wingworm

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    Mar 1, 2014 at 4:44 PM #2
    wingworm

    wingworm

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    Details:

    1. Motherboard: GA-H77TN by Gigabyte, may upgrade to GA-H87TN later for haswell platform.

    The original iMac G4 mother board was kept for IO connector reuse and for fixing the new mother board. Remove the useless components on top side using hot wind gun, except the IO connectors and the Class-D amplifier circuit around the chip TA2024. Then drill holes on old board accordingly and mount the new thin mini-itx board with screw. The mounting position can be referenced to the picture, make sure the original 4 screw holes connecting to the dome are not overlapped.

    2. IOs
    All available IOs are extended through the original IO connectors on original mb by soldering to correct pins. Ethernet and USB2.0 ports can be soldered pin-to-pin directly, while USB3.0 is realized with additional 4 high speed signals (RX+/RX-, TX+/TX-) going through original 6pin 1394 port. An external adapter cable is built by a USB3.0 female connector (9pin) <==> USB2.0 male connector (5pin) +1394 male connector (4pin)

    3. Heat removal of CPU
    Keep the original solution by using heat pipe to conduct CPU heat to the heavy metal dome, a natural perfect heat tank. The three metal heat-sinks are reused, but the two heat pipes are customized design. A piece of aluminum foil is used to tighten the heat-sink.
    All these are done to keep the height as low as possible, for the space of DVD drive.

    P1041605.JPG
     
  3. wingworm

    wingworm

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    Mar 1, 2014 at 4:55 PM #3
    wingworm

    wingworm

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    4. Audio output

    The initial and common solution from most mods is to use an extension connector from headphone jack of mb, but this will lose the function of jack detection. Then motherboard will always detect a headphone is present, and no audio will go to the internal speaker.
    Here the solution is to use the Front Panel Audio Header of the motherboard, which includes a jack detection signal (F_LINE_JD). That’s the one of advantages of using standard motherboard.

    The only problem is that the original iMac G4 3.5mm headphone jack uses old detection mechanism – two pins shorted by default and disconnected when headphone is present, while the new Intel HD audio uses below mechanism – FIO-SENSE and SENSE-RETURN are disconnected by default and shorted when headphone is present.

    front_audio_panel.png

    Thus, a logic reverse circuit is designed to adapt this. The 2.5mm mini jack detection function for pro speaker is also implemented in this circuit. The jack detection of pro speaker is simpler, the detection pin (2.5mm_JD) is +5V by default and goes to 0V when pro speaker is inserted.

    jackdetection.png

    The details of the circuit are: When 3.5mm headphone inserted, 3.5mm_JD is disconnected with 3.5mm_L (left channel audio signal), and then 3.5mm_JD is pulled to +5V by R5, and Q1 is then turned on to short F_LINE_JD to GND, which is connected to pin10 of the Front Audio Panel Header on GA-H77TN.

    Q2 is used to inverse the jack detection signal of pro speaker, D2 together with D1 are the OR logic to trigger the 3.5mm jack detection.

    TA2024_EN is used to disable the Class-D chip on original mb when pro speaker is not present or headphone is inserted.

    This circuit board is then taped in slot of original airport card.
    Now the logic of audio output is kept as same as original iMac G4, that is: the internal speaker goes mute when headphone or pro speaker is inserted, the pro speaker goes mute when the headphone is inserted.

    Please note there’re two options of the onboard jack detection circuit according the ALC887 datasheet, while GA-H77TN uses the option 2, and the above headphone and pro speaker jack detection logic circuit also only applies to option 2.

    IntelHDAudioOptions.PNG
     
  4. wingworm

    wingworm

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    Mar 1, 2014 at 5:03 PM #4
    wingworm

    wingworm

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    5. Native Pro Speaker support.

    The beautiful eyeball pro speaker is the unique part of iMac G4, hence most iMac G4 MOD tries to keep it. It’s passive and power cableless which makes Jobs’ all-in-one conception. However, the integration of onboard amplifier and a proprietary 6pin 2.5mm mini jack make reuse of the pro speaker quite difficult. By searching the web, most of the pro speaker MODs needs cutoff to the wire, this will obviously degrade the elegance of iMac G4.

    In this MOD, since the original mother board is remained, the original mini jack for pro speaker and the onboard amplifier can also be reused. By plugging into original mini jack, the four wires out of six which connected to two speakers can get through to the output of the amplifier directly, hence no need to cut off the connector.

    Reuse of the amplifier is also easy, the onboard circuit is almost the same as the application in the datasheet of the class-d chip TA2024. Just connect audio signal to the two input dc decoupling capacitors which locates at pin 11 and pin 16 of TA2024. The chip is power by +12V which can be drawn from sata power connector, this can completely shut off the chip in the standby. The jack detection controlled signal TA2024_EN is connected to the sleep pin (pin 18).

    TA2024_Application_Circuit.PNG

    P1041602.JPG

    P1041601.JPG
     
  5. wingworm

    wingworm

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    Mar 1, 2014 at 5:07 PM #5
    wingworm

    wingworm

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    6. Reuse of Power Supply.

    GA-H77TN supports 12~19VDC wide range input voltage, the original power supply can be easily reused. The only mod is replacing all the short life electrolytic capacitors with new ones from Nichicon.
    Since the on-hand 17" version power supply only provide 12V output, an external 12v to 24v dc/dc boost converter is used for backlight power of LCD panel. No need of this is to 20" version power supply, which already has +24V output.

    P1041590.JPG
     
  6. wingworm

    wingworm

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    Mar 1, 2014 at 5:12 PM #6
    wingworm

    wingworm

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    7. LCD panel.

    Lots of references already exists on how to reorder original TMDS signal to hdmi connector or dvi connector. Here just shows a small extra feature to automatically turn off 12V panel supply voltage when display is off. +5V DDC power from HDMI connector pin18 is used to turn on/off the PANEL VCC, which is also used to turn/off the backlight power. This will save around 4 watt for panel power when in standby mode. Now the total standby power from AC line is about 5 watt, no need to unplug the AC power every time.

    hdmi_connector.jpg

    panel_vcc.png
     
  7. wingworm

    wingworm

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    Mar 1, 2014 at 5:16 PM #7
    wingworm

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    8. Drives.

    Though every effort is tried on lower the profile, it’s still about 1cm higher to hold a full size optical disc drive. Instead, a 1.27cm high notebook DVD combo drive is used, while this lose the auto motion of the disc tray. Fortunately the eject action of notebook optical disc drive can open the door.

    P1041588.JPG
     
  8. wingworm

    wingworm

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    Mar 1, 2014 at 5:18 PM #8
    wingworm

    wingworm

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    9.wifi and Bluetooth.

    A mini pci-e module supporting wifi and Bluetooth is used, and the original antenna is reused.

    P1041592.JPG

    10. fan

    Original fan is resued.
     
  9. wingworm

    wingworm

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    Mar 1, 2014 at 5:37 PM #9
    wingworm

    wingworm

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    11. Assembly and finished

    The original internal architecture is kept, from topside are fan, power supply, hard drive, optical drive and the motherboard

    P1041606.JPG


    The back io ports and cover is remain complete, and all usb/ethernet/headphone/pro speaker jack are functional.

    iocover.JPG

    The front door can be opened by the 1.27mm optical drive

    P1041625.jpg

    The new iMac G4 running windows 8. (hackintosh would be the next)

    P1051633.jpg

    with a real lamp:)

    P1051641.jpg
     
  10. ersterhernd

    ersterhernd

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    Mobo:
    MSI Z77MA-G45
    CPU:
    i7-3770k @ 4.3 GHz
    Graphics:
    Gigabyte R9 280X Windforce 3GB
    Mobile Phone:
    Android
    Mar 2, 2014 at 12:28 AM #10
    ersterhernd

    ersterhernd

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    Mobo:
    MSI Z77MA-G45
    CPU:
    i7-3770k @ 4.3 GHz
    Graphics:
    Gigabyte R9 280X Windforce 3GB
    Mobile Phone:
    Android
    I've seen a lot of great mods on these forums, but this ranks among the very best.

    How in the world did you figure all that out, and make it fit in the dome????


    Excellent, 10/10 for sure.


    Cheers!
     

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