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    Imac G5 Video/Display problems.

    Hello and happy New Year!.
    Today I received an Imac G5 20" 2.0Ghz producing no video except a dark purple tinge.It would display on an external monitor and I managed to run ASD which showed no errors in video or any other component,all 3 diag leds were on.No overheat led was displayed.I changed the inverter and screen with same make model.No video.
    Time to look very carefully at the caps.Three to the right of the CPU housing looked slightly odd,not in your face bad,but I pulled them anyway.Using my Atlas ESR meter with probe compensation,1 measured 8ohms,another 6,the last 5.Recapped with Nichicon HZ's rated at 1800 @ 6.3v.Reassembled to see the results,no video.
    Time to pull the lot.The Ruby 1000 @ 16v x5 were all spot on.So far,twenty of the Chemicon KZJ 1800 @ 6.3v have all measured between 2200-2400 on the cap scale at 0.00 Ohms.
    I know these are above rated but they still fall in the 20% margin,just!.I've only had a video signal problem once before so my experience is limited on this one,the cause of the other one was a faulty LVDS cable,but as I've said above,I ruled out any other possibility.
    In any bodies experience,would a bad cap(s) be the cause of this problem or could any one with a similar experience point me in the direction of a possibe failure in another component.I had a look at the video connector on the board with a magnifying glass,the solder joints look fine,but if there is a test I could perform with a DMM,please let me know,
    I really would appreciate the help!.
    Last edited by deckart; 01-05-2010, 07:22 PM.

    #2
    Re: Imac G5 Video/Display problems.

    Suspect that your problem's due to a failed ball array that connects the GPU to the logic-board. For some reason this video failure symptom is more prevalent in the 17" G5 series than the 20". But when you replace all caps on a G5 board & there's still no video...it's likely that the GPU's separated/separating from the board. Strange that you get positive diagnostic light indicators, or that ASD did not detect a failure point, but the fact that you can attach a secondary display successfully underscores that the on-board video chip's involved. The G5 iMac's GPU is like a laptop in that it's soldered directly to the logic-board, & over time the ball arrays detach at the outer corners (due to extreme heat or stress).

    There are a number of services (some on ebay as well) that accept G5 logic-boards for BGA re-ball...however, none that are reasonably costed ($75 or less) have much of a track record for returning logic-boards functional, or returning boards at all, for that matter...so beware. GPU Medics is a one-man operation that offers such a service at an affordable price, however, google his client reviews before trusting your board to these firms. Superior Reball and Rework is another, slightly costlier, option.

    I have 3 G5 logicboards that will not post video after recapping. Although mine are all 17" 1.8GHz or 2GHz, they disable the 3rd diagnostic (video) light at power-up, as they should when the GPU's failing.

    So, you'll probably need to find someone trustworthy that has BGA re-ball templates for the G5 & a hi-end, temp-controlled rework station, as well as the ability to X-Ray the joins to make sure the re-attachment is sound.

    Wish there was better news about this...but I haven't found a simple cost-effective solution yet.

    Cheers
    Daniel

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      #3
      Re: Imac G5 Video/Display problems.

      Hi dbridgma,
      I had kind of figured it was a failing GPU,but being able to attach an external kind of threw me.There are no lines or glitches that usually point to a BGA problem and pressing down on the chip does nothing.I've got so many of these with a bad chip that I'm going to bite the bullet and get a BGA reflow system.http://blundell.co.uk/detail.php?id=irplrpc550
      They also do training.I figured that to recoup my initial outlay just reballing/reflowing Imacs 1/2/3rd revision wouldn't be enough,so will do xboxes etc.
      It will be nice to be able to fix these machines now and not consign the LB to the scrap heap.

      Comment


        #4
        Re: Imac G5 Video/Display problems.



        External connected to the 2nd video chip.....???

        Think.
        veritas odium parit

        Comment


          #5
          Re: Imac G5 Video/Display problems.

          Hi Toasty,intriuging.2nd chip on main GPU?.

          Comment


            #6
            Re: Imac G5 Video/Display problems.

            No. You missed the point. I was being facetious.

            If video is working fine on external connection, then it's -not- the GPU.
            If a 2nd -known working- screen does the same, and your screen works in the other, then it's -not- the screen.
            What's in between?
            veritas odium parit

            Comment


              #7
              Re: Imac G5 Video/Display problems.

              Ok.My diagnostics,3rd LED on, LB lights up.No fans go into overdrive,sign of hardware fault.MAIN screen stays dark purple,inverter replaced no screen still.Pull mid-plane and try in known good screen and chassis.No display.This eliminates,
              Screen,
              Display connecter,
              Inverter.
              Try known good PSU,just in case it's not putting out 20/24v to power display,no display.
              I'm missing something,I know,but logically power-LB-CPU-GPU-display.
              What am I missing Toasty?.

              Comment


                #8
                Re: Imac G5 Video/Display problems.

                Failure is (obviously now) on the midplane. Whatever is between the GPU and the display connector on the midplane. I'm not tearing mine apart to trace this.

                See these links. Maybe one will help:
                http://support.apple.com/kb/TS2094
                http://forums.macosxhints.com/showthread.php?t=98925
                http://support.apple.com/kb/HT1379?viewlocale=en_US
                http://forums.macosxhints.com/showthread.php?t=43811 (check the serial numbers in Post #3)

                I am unsure of the "wiring" from GPU to onboard display video vs. external video connection. The one suggestion was to double check the connector from midplane to video display and to re-seat it. Seems a common problem after a recap from what I'm seeing.
                veritas odium parit

                Comment


                  #9
                  Re: Imac G5 Video/Display problems.

                  Thanks for the links Toasty.
                  Still none the wiser,tracing back from the display attachment,all roads lead to the Hynix memory chip or to the Nvidia GPU.So still up the swanny because they are both BGA.
                  Maybe in the next few days I'll have a senior moment and figure something out.

                  Comment


                    #10
                    Re: Imac G5 Video/Display problems.

                    Hynix? Spits. This was Hyundai memory maker. Years ago I had *terrible* run with memory chips from that particular maker. *Multiple failures* on same stick or memory bank, normally would see just one chip fail. But not this.

                    For this reason, I avoid these and I have no problem since.

                    Cheers, Wizard

                    Comment


                      #11
                      Re: Imac G5 Video/Display problems.

                      Bad onboard display connector?

                      Does display work with good mainboard?
                      veritas odium parit

                      Comment


                        #12
                        Re: Imac G5 Video/Display problems.

                        Has anyone figured this out yet? I have a iMac G5 2GHz that will display video to an

                        external monitor but no video to the internal LCD. I popped in a 1.6GHz logic board and

                        the internal LCD works fine.

                        Comment


                          #13
                          Re: Imac G5 Video/Display problems.

                          Check the screen cable receptacle on the non outputing main board and check you have not damaged the tracks on the pcb. The GPU feeds the external video ouput and the internal lcd, there are however seperate buffer/drivers for the two devices the one to the lcd path may have failed. Aso check that the caps you have soldered in are not badly soldered and shorting the +ve to these buffer drivers. And of course do some voltage comparisons between the good board and the bad one. Its a luxury if you have a good board to compare with and even more so if you have a scope
                          Last edited by audioreplica; 03-03-2011, 11:28 PM. Reason: spelling and additions

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