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    #1

    iMac G5 - works only when cold booted

    So, I have this first generation iMac with Nvidia FX 5200, 17" model. The thing is that the machine works only when booted cold. I can play Halo for example without any problems and surf the web and so on. If I power down the machine after some use and let it cool a little it shows artifacts and usually locks up. When it is in this "artifacting mode" Apple Hardware Test says that the GPU is the fault, when booted off cold all tests pass without problems.

    Very confusing, I have changed couple caps, there were two which were bulging. Capacitors which have not been changed are Rubycon MCZ -type which should be reliable? Power supply might also contain bad caps but it has security screws so I cannot open it and have a look.

    Does this sound like a cap issue on motherboard or PSU or is it solder cracks on the GPU? What do you guys think?
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    #2
    Re: iMac G5 - works only when cold booted

    thats a tough one for me.

    rubycon mcz's should be just fine, unless the thing hasn't been turned on in 10 years, and considering the thing was made in at least 05 thats not possible

    hmm................

    anything like this?

    http://www.youtube.com/watch?v=yXgPJRA7QC0

    it might be heat related (as in too much). does it crash if its on for a long time while playing?

    I heard it might be a logic board problem, but a lot of that is caused by those caps you replaced. so I don't know. do some google research, only you would know more of the specifics

    hmm lookie at this

    http://farm4.static.flickr.com/3190/...4130c0d332.jpg

    I have a funny feeling that heat might be killing these caps, so it does not matter if they're mcz's or not if heat dried the electrolytic up, it can cause wierd stuff. don't quote me on this, as so far as I know, warming caps up usually work, not cold caps

    its also plausible that the bad caps damaged your gpu, or your power regs in some way
    Cap Datasheet Depot: http://www.paullinebarger.net/DS/
    ^If you have datasheets not listed PM me

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      #3
      Re: iMac G5 - works only when cold booted

      Here is video about the whole thing:

      http://www.youtube.com/watch?v=5otU5...ature=youtu.be

      The machine was on for some time before I started to record. Beforce boot up it had been off for plenty enough time for it to cool down, the power cord was plugged in the whole time. Basically I play some alo, run some GioFX Openmark which displays OpenGL ball spinning and then I watch some Apple commercials. No problems, no artifacts, I have played Halo much longer, for about 30 minutes. The fans of course run like crazy because G5 is such a heat generator despite being slow as shit. Power down, wait a while, artifacts on boot and the machine hangs. It has repeated this same thing many times.

      None of those Rubycon caps look faulty. There is no visible burn marks anywhere, not even under the heatsink on CPU or GPU.
      Last edited by thewk; 05-21-2012, 06:10 AM.

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        #4
        Re: iMac G5 - works only when cold booted

        Non-bulging caps doesn't mean they're good. Also, have you checked the power supply caps?

        Artifacting usually means a fault in the GPU on these (bad BGA) and having them reflowed corrects the problem. The mainboard caps should replaced, sans the poly ones.

        Check the video connector between mainboard and display (the one with the 2 screws). Bad connections here have been issues too.

        BCN sells the standard recap kit for these:
        https://www.badcaps.net/store/produc...&products_id=3

        You can also inquire of the poly-mod price.

        Reflowing can be done for ~$100, and the shop you choose to send it to should be capable of testing it before it is returned and give you a warranty of at least 90 days.

        Toast
        veritas odium parit

        Comment

          #5
          Re: iMac G5 - works only when cold booted

          Well the power supply has those security screws so I can't open it. Would it make sense that there could be one big capacitor which has slightly failed and the time needed to wait is not actually for the GPU to cool down but for the capacitor to completedly discharge? Or same kind of thing for one or more caps on motherboard? Just guessing.

          Comment

            #6
            Re: iMac G5 - works only when cold booted

            Security Torx can be had at Lowe's or Home Depot. Just need the 1/4" drive bit type.

            Regarding your question, no. If it's good from cold, then it really seems to point to the GPU BGA problem.

            You're going to need to recap it anyway, including the PSU. These run very hot and those caps are cooked by now.

            Make sure you clean out the lower fan inlet and the fins on the bottom of the GPU heatsink. They get clogged very badly.
            Last edited by Toasty; 05-21-2012, 09:12 PM.
            veritas odium parit

            Comment

              #7
              Re: iMac G5 - works only when cold booted

              A cap replacement in the PSU is easier and cheaper than a GPU reflow...
              Try it first!

              Comment

                #8
                Re: iMac G5 - works only when cold booted

                Well it is probably GPU fault, I'm starting to agree. I booted the machine without the back cover in this "artifact mode" and when I applied some pressure back and forth where the GPU is located (heatsink was in place of course) and I was able to change the artifacts according to whether or not there was pressure. I'm not unfamiliar to this solder issue, just based on my previous experience FX 5200 usually does not fail atleast on these machines but it seems that this is the case now. Altought usually it has been so that there is no picture at all on boot or the machine hangs under extreme load, this case is bit weird because there is picture when the machine is cold and extreme load does not crash it.
                Last edited by thewk; 05-22-2012, 12:22 PM.

                Comment

                  #9
                  Re: iMac G5 - works only when cold booted

                  Well it seems that I cannot edit my last message, but today I decided to replace the two caps near the GPU and the video data cable and now atleast couple times I have been able to first heat the machine up with Halo, then put the machine to sleep and wake up succesfully after letting it cool down a little while in sleep mode. I used bit "overspecced" caps made by Sanyo, originals were Rubycon 1800uf 6.3v and these are 1800uf 10V, most of the time when I replace caps I actually use ones rated bit higher, on microfarads or volts or both. So far it seems now be working great but lets see. In addition to the standard artifacting (lines etc.) the machine displayed same kind of symptoms like an old TV could probably display, this led me to believe there was something wrong with the voltage. Sometimes when I booted machine the fans were spinning at maximum speed for a brief second and then the machine booted succesfully so it was like the machine was near to crash but then didn´t after all.
                  Last edited by thewk; 05-23-2012, 06:03 AM.

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                    #10
                    Re: iMac G5 - works only when cold booted

                    Update to this. I mentioned that fans were spinning at maximum, in addition to this there was also red led which means overheating. I disassembled the machine and tried to create a kind of "shim" between the heatsink and the gpu, currently I do not have copper plate which I know is the only real option for shim. I did have some thermal conductive mat (or something, I don't know how to describe it, english is not my main language....) After this the machine seemed to be stable in use, I played some 3D games, surfed the net etc. no problems. Before it would hang when just looking at console messages or at similar kind of strange situations. After I did install updates and tried to restart, the machine hang. On reboot there was this red led again but after brief moment the machine booted. After some research I noticed that even when I was running the machine without the back cover and not doing anything which taxex hard disk, its temperature would be at 50C, plus or minus couple degrees. After this I brought in a big fan, you know those kind which you use to cool yourself (sorry about my english again) and adjust it to blow directly to hard disk (and gpu at the same time, I think) the machine seemed to become rock solid, played games, surfed internet, ran Xbench and ran Rember memory test for couple loops, in between these I rebooted the machine 3 or 4 times total and no sign of red led and no hang ups.

                    So I guess that this really is a case of overheating?

                    Comment

                      #11
                      Re: iMac G5 - works only when cold booted

                      I have a 20" G5 .

                      The problem are cause mouse freeze ,system crash after using for a while.

                      My experience is the CPU & GPU not overheat,the DRAM is.(HDD is very hot too)

                      Because the DRAM to HDD air flow is not good enough to carry out the heat.

                      My solution is change 3.5 HDD to 2.5 HDD and put a laptop CPU fan beside HDD to increase air flow.

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