Results 1 to 7 of 7

Thread: G4 Imac 20" screen - no video

  1. #1
    Join Date
    Nov 2005
    Location
    Sydney-Australia
    Posts
    55

    Default G4 Imac 20" screen - no video

    I have just bought a 1.25 GHz G4 Imac ( OS10.3 ) cheaply that has no video showing. The machine boots , chimes etc but the screen stays black. I get this in a couple of days and want to get it up and running hopefully as a Xmas present for my other half. I am hoping that the screen is OK and that it is either a motherboard, inverter or video problem instead. First I want to plug in another monitor via the mini-VGA connector and see what happens. If I'm correct then I should see the mirrored desktop on the attached monitor.If it's the motherboard I was wondering if I can't pick up one from this model then maybe I can get one from the 17" 1.25 GHz model and slot that in. From my research it seems that these two computers are identical in every way except for the screen. Would this be possible ? Just wondering if someone else has done this before.If I can't fix this computer then I will part the machine out and easily recoup what I have spent so far.
    Stewie

  2. #2
    Join Date
    Feb 2001
    Location
    on the landline, Mr. Smith
    Posts
    7,787

    Default

    Sounds like a plan.

    I would guess you are correct, and as long as you are correct about the video chipset being the same, the logic boards are likely interchangeable.

    If you get video out from the mini VGA, that leaves you with everything working in the lower case and the LCD, the cabling that runs through the neck, and how it attaches to the logic board as possible problems.

    Have only done minor surgery on G4 imacs, so I can't tell you much beyond cracking one open to get to the internal RAM slot. I don't know of anybody here that has cracked open the neck or LCD case on one......if you do google a take-apart guide or info, post back and share the wealth.

    Good luck, and let us know how it goes.
    "Imagine if every Thursday your shoes exploded if you tied them the usual way. This happens to us all the time with computers, and nobody thinks of complaining." -- Jef Raskin

  3. #3
    Join Date
    Aug 2005
    Posts
    200

    Default

    The LCD screens on the laptops have a separate inverter board that powers the LCD screen. I am not sure if there is a similar board in the G4 iMac. You might want to check out iFixit.com they can provide a good deal of info on the disassembly of many of the macs they are also a source of parts.
    good luck. My better half saw one of those iLamps at the mac store over the weekend and liked it enough that she might start using a computer. She just thought it was pretty.
    Bob

  4. #4
    Join Date
    Nov 2005
    Location
    Sydney-Australia
    Posts
    55

    Default

    Yeah I have the service manual CD ( vers 2.0 ) so I have had a good look at it to see whats involved.If anyone wants a take apart pdf from this or any other mac email me. Inside is pretty tight but if I take my time and test everything then I should be able to resolve this problem. The Imac does have an inverter card so that may be one aspect as to why no video. The specs at Everymac and the service manual also indicate that the two logic boards are identical so a swap from a 17" model I think is possible. I saw one of these about six months ago that a customer had done a hack on and installed a blue LED light in the base. It was on a glass top desk and with the computer on at night and the only other light in the room being a soft wall light , the base and the glass top were bathed in this soft blue glow. It looked fantastic. If your other half liked the one in the store she would have loved this one .

  5. #5
    Join Date
    Mar 2001
    Location
    Virginia... where one Democrat CAN make a difference
    Posts
    2,929

    Default

    This may be too obvious.... but the backlight is working?
    Damien,

  6. #6
    Join Date
    Nov 2005
    Location
    Sydney-Australia
    Posts
    55

    Default

    Wouldn't that be good if that was all that was wrong with it ! I'll find out on Saturday when I pick it up.This model does have an inverter board which appears to be both relatively easy to find and replace if necessary. IFixit only seems to cater for ipods and Powerbooks.
    Stewie

  7. #7
    Join Date
    Nov 2005
    Location
    Sydney-Australia
    Posts
    55

    Default

    Works kinda haywire at the mo so this will be investigated over Christmas

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •