checkerboard fuzzy screen then freezes

whenever i start up my computer after about 10 minutes (sometimes quicker) i get a fuzzy screen where there are fuzzy rectangles and clear rectangles in a checker-board type style. initially it's possible to click on the desk top, then back on the open window and still use it, but then the clear parts go fuzzy too, and the circle of death comes up. Won't go to sleep, just have to power it down with the button on the back. any idea what's wrong?

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You iMac is probably suffering from bad capacitors, this problem plagued iMac G5's, and requires replacing about 25 capacitors on the computer's logic board (Or The Board Itself), this is a degenerative problem that starts out with freezing, and doing what yours is doing, then worsens to the point of not turning on. If you want to verify this, open the back of your iMac, and check the capacitors, for bulging, leaking, and corrosion, capacitors are cylindrical components on the logic board a little less then a centimeter in diameter.

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Thanks chris, i'll have a look this weekend. i've had a look at a couple of sites and this looks like a real work up to fix (particularly for someone with no soldering experience). Do you know anyone out there who is doing this commercially? guessing that might not be cheap though.

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There are some ebay sellers who give you the option to ship them the computer, then they repair it and charge you afterwards, but you'll likely pay over $200

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I checked the capcitors a while back, and they all looked fine; no bulging, leaking etc.

i took it to the genius bar at the local apple shop, chap there said it was the video card. part of the main board, over $500 including labor to fix.

it's got worse to the point where it might not boot up all the way, and if it does, it goes bad very quickly.

i've eventually capitulated, and been and bought a new iMac. i'd got everything backed up with time history, so haven't lost anything (other than a LARGE wad of cash)

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Capacitors can bulge or burst on the bottom as as the top. When this happens it is not easy to see or you may not be able to see it at all until that capacitor has been removed. The iMac G5 was plagued with capacitor problems

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I've sent in a couple of boards for cap replacement that I found on eBay. I forgot the name but they were out of Utah. I believe they charged me about $87.50 each. One board worked fine when returned the other booted but would never take a system installation.

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So is it worth spending the £400 / $500 to fix it or do people recommend getting a new iMac model that hopefully won't suffer from these problems in the future?

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Definitely get a new machine. The video on this model is integrated, so they are just replacing the board (i.e. the whole machine) anyway. For that much money, you can pick up a used Intel iMac. These G5s are very problematic and in my opinion not worth depending on.

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After replacing all of the power supply capacitors with load-ESR type (as required) my 20" fired up but had the same problems as before. I believe the problem is more likely to be around the video circuit.

Anyone else discounted the power caps and found the cause?

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the "checkerboard fuzzy screen" is a graphics processor related problem. the G5 series had most likely 3 problems: 1, bad capacitors on the logic board 2, bad capacitors in the power supply unit and 3, faulty solderings under the graphics processor. fixing the solderings is possible - the best way would be replacing/reballing the graphics processor - but that might be a little bit expensive. it's also possible to "reflow" the solderings with a hot air- or infrared soldering station. it's not easy and if you don't know what you're doing - you could kill the logicboard and even if it worked - none could tell how long it would last - sometimes a few days, most of the time month and sometimes years.....

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stuart horswill will be eternally grateful.
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