My PiMac Build (2008 20" iMac)

Discussion in 'iMac Mods' started by CostasV, Feb 8, 2017.

  1. CostasV

    CostasV

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    Feb 8, 2017 at 7:07 PM #1
    CostasV

    CostasV

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    Hi All,

    I would like to share my experience building a custom iMac using a Raspberry Pi 3 as the new motherboard. I still have some quirks to fix, but it works very well already!

    Build Info:
    2008 iMac
    Original 20" LCD
    Original power supply
    Original fans
    Original speakers
    Raspberry Pi 3 ($39)
    LVDS controller with inverter and control board ($23)
    4-port USB hub ($7)
    HDMI-to-VGA adapter ($8)
    USB car charger ($10)


    Build Notes:
    Power: I wanted to reuse the power supply, as it was working and easily provides enough juice to power everything. It only outputs 12V, so I used a USB car charger to drop the voltage to the 5V that the Raspberry Pi needs.

    LCD: The LCD was still working, so I ordered a LVDS controller. Unfortunately, the Ebay seller said he couldn't get the HDMI-based board to work this this type of LCD, so they shipped me one that only has VGA input. I was upset about this, but it took long enough for them to get me the controller board, I just went with it. Given the RPi does not have a VGA output, I initially tried to use a Gerts VGA666 controller board that uses the GPIO pins to generate a VGA signal. The quality of the result was mediocre, so I ordered a HDMI-to-VGA adapter (unpowered). Initially the LCD would blank out every so often (dependent on screen resolution, full res it was barely usable). The solution was the use the config.txt to boost the HDMI signal to the max. I am pretty sure I did not need the inverter for the LCD cathodes tubes, as the original still worked, but did not want to bother rewiring the plugs to make it work. I did not have a short enough VGA to link the controller to the VGA adapter, so I used a spliced ethernet cable. There does not appear to be hardly any signal degradation.

    Speakers: The original speakers still worked, so I simply spliced the cables onto 3.5mm jack that plugs into the RPi. I initially tested it on my smartphone and it worked, albeit with a medium-to-low volume output. I do not plan to use much sound on this machine, so that is acceptable. When I plugged it into the RPi, there was no sound. I believe the RPi is trying to pass audio over HDMI and not 3.5mm, so I will need to work that and configure it to force audio over 3.5mm.

    Fans: There are 3 fans in the iMac. They all run off 12V power and have 4 wires. The larger fan that cooled the PSU and the heatsinks used a special 5-wire plug. After testing, the two smaller fans simply need a 12V power and a 3-5V control voltage to adjust the speed. I plugged them into the 3.3V that the RPi outputs and they work well (5V was a little too noisy and unneeded). The larger fan appears to be a PWM fan, hence the different plug. I attempted to use a 555 timer circuit to create a PWM signal (I found the schematics online), but it outright did not work. I will attempt to drive the PWM signal from a GPIO pin from the RPi using a simple Python script. Potentially I can have it adjust speed based on the CPU temperature if it is not too hard. I currently do not have the large fan inserted, but after and hour of use, the high-temp warning signal turned on on the RPi. Therefore I will need to get that working.

    USB: The iMac's ports in the back are a little bit of a pain to use, as they are perpendicular to the LCD and such. I simply used a USB hub and had it's ports face down and out the memory access area at the bottom.

    On/Off Switch: The PSU of the iMac uses a simple short to turn itself on. Given the stock switch on the iMac is a momentary button, I could not use it directly. I fiddled with the idea to keep it and build an on/off circuit, but given the on/off style of the RPi, I simply went with a rocker switch. I cut the dividing plastic between two of the old USB ports on the back of the case and the rocker switch fits perfectly. I added a 1k ohm resistor in line just in case.


    Let me know what you guys think! IMG_20170207_192234.jpg IMG_20170207_195651.jpg IMG_20170207_201947.jpg IMG_20170207_202221.jpg Layout.png
     
  2. MacTester57

    MacTester57

    Joined:
    Dec 15, 2011
    Messages:
    907
    Mobo:
    Z68MX-UD2H-B3, DQ77KB, NUC DC53427HYE, NUC D54250WYKH
    CPU:
    i5-2500K, i3-3225, i7-3770S
    Graphics:
    HD 3000, HD 4000, HD 5000
    Classic Mac:
    iMac, Power Mac
    Mobile Phone:
    iOS
    Feb 13, 2017 at 9:32 PM #2
    MacTester57

    MacTester57

    Joined:
    Dec 15, 2011
    Messages:
    907
    Mobo:
    Z68MX-UD2H-B3, DQ77KB, NUC DC53427HYE, NUC D54250WYKH
    CPU:
    i5-2500K, i3-3225, i7-3770S
    Graphics:
    HD 3000, HD 4000, HD 5000
    Classic Mac:
    iMac, Power Mac
    Mobile Phone:
    iOS
    The first iMac mod for a long time. Well done!

    MacTester
     
  3. CostasV

    CostasV

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    Mar 6, 2017 at 1:02 AM #3
    CostasV

    CostasV

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    Well, after some usage, my wife forced me to swap out the really underpowered Raspberry Pi 3 for something that could actually open a normal website like LinkedIn or YouTube. I guess I never realized weak this little SBC is.

    I looked through all my scrap and found an old HP 2133 netbook. Even this terribly underpowered single-core VIA processor worked MUCH better than the quad-core ARM processor. I took out the PSU, RPi3, speakers and power perfboard, and put in the netbook motherboard and netbook speakers. It worked somewhat okay, but even being faster than the RPi3 wasn't saying much. I tried to live with it for a week, but it was pretty useless (a reason why the netbook was in the scrap pile).

    I actually had a windows Core2Duo laptop that just had the LCD die on it (cathode fried). I now am simply using the iMac as an external monitor for that LCD-less... All that work for nothing. Oh well, at least its a nice looking external monitor. No chance the motherboard of this laptop could fit inside the iMac.

    In hindsight, I should have simply ordered replacement parts for the iMac off eBay, would have been cheaper and easier.
     
  4. Jascha

    Jascha

    Joined:
    May 16, 2011
    Messages:
    16
    Mobo:
    MSI P67A GD55
    CPU:
    Core i7 2600K
    Graphics:
    Gainward GTX460 GS
    Mac:
    MacBook Pro
    Mobile Phone:
    Android
    Mar 6, 2017 at 9:41 AM #4
    Jascha

    Jascha

    Joined:
    May 16, 2011
    Messages:
    16
    Mobo:
    MSI P67A GD55
    CPU:
    Core i7 2600K
    Graphics:
    Gainward GTX460 GS
    Mac:
    MacBook Pro
    Mobile Phone:
    Android
    Why don't you go for a "el cheapo" NUC or a similar form-factor mini PC? They are around 200 Dollars and pretty powerful - enough for webbrowsing and youtube. Or maybe a used Macbook Air logicboard from ebay? ;-)
     
  5. warkentim

    warkentim

    Joined:
    May 6, 2017
    Messages:
    5
    Mobo:
    GA-Z170N-WIFI
    CPU:
    i7 6700k
    Graphics:
    Nvidia 770 FE
    May 6, 2017 at 11:21 PM #5
    warkentim

    warkentim

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    May 6, 2017
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    Mobo:
    GA-Z170N-WIFI
    CPU:
    i7 6700k
    Graphics:
    Nvidia 770 FE
    Curious if you could specify which LCD controller you used? I am getting super curious as to wether or not I could pull this off as well..
     
  6. CostasV

    CostasV

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    May 11, 2017 at 7:25 PM #6
    CostasV

    CostasV

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    I wanted to get the M.NT68676.2 off Ebay (for the M201EW02 v8 panel). The seller sold me a different one without HDMI input, saying he couldn't get that one to work with the display. I suspect he was trying to con me the price difference, which he refunded after a few messages. I can't find the model number right now of the one he actually sold me. It works okay, but have 2 issues:
    First, it never turns the LCD off if there is no signal (i.e. laptop turned screen off), it just stays bright white.
    Second, there is some noise in the signal. Not noticeable at all when there is an image, but if screen is black or near black, you notice.

    I don't think I would attempt this project again. The iMac G4 looks like a more unique chassis to work with in the future.
     
  7. Renton07

    Renton07

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    Oct 14, 2017 at 8:01 PM #7
    Renton07

    Renton07

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    Dec 14, 2015
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    Hi CostasV,
    I want to do the same mod as you, but it is hard to find some information on the internet.
    How to use the 4 wire speaker to jack ? I think using an RCA cable, but i don't know how to connect it with 4 wires.
    How can i use the original power supply like you ?
    I do some research, but nothing clear.
    I read your thread https://www.tonymacx86.com/threads/need-help-imac-raspberry-pi-pimac.212021/ and see the result here, but you can't tell how you resolve it.
    Thank you very much for any help you provide.
     

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