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iMac Intel 27" EMC 2309 (Late 2009, Core 2 Duo 3.06 or 3.33 GHz) ID iMac10,1, EMC 2374 (Late 2009, Core i5 2.66 GHz or Core i7 2.8 GHz) ID iMac11,1

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Intermittent black screen (both lcd and backlight)

iMac 27" 2.66 GHz Core i5 (Late 2009)

The machine is now 7,5 years old. A week ago it started with some flickering and a black screen for some seconds, but each day it became slightly worse to the point it was almost impossible to get something on the display. I took it to the Apple store for repair, but they say the machine is too old and they couldn't get the needed parts anyway.

Some experiences/tests I did:

  • The display can turn black anytime. It doesn't seem to be temperature-related. It even seems to be harder to get it working in the morning than when the machine is warmed up. But then it also happens sometimes when the machine is running for some hours.
  • Sometimes I can bring it back with 2x power button or 2x cmd-alt-eject
  • It's not the backlight, because the screen becomes totally black.
  • All four diagnostic leds are working. When the screen becomes black led 4 stops.
  • When I connect the iMac to an external display both displays show the same behaviour.
  • With the inverter-board disconnected and the iMac connected to an external monitor it still happens.
  • Disconnecting v-sync doesn't do anything.
  • When I use the iMac as a display for my windows pc through target display mode the problem hasn't occurred yet.
  • I did an Apple hardware test which told me the hdd fan motor needed repair. So I disassembled it, disconnected all cables, made it dust-free inside, cleaned all three fans etc and put everything back inside. It did help for some time. But after an hour of uptime the problem showed again. And it happened again when it powered up this morning. This performance is way better already compared to the days before, but it's still there. (Also the fans are ok now according to another AHT, but I don't think that was related)
  • See kernel panic report I see this: Kernel Extensions in backtrace:

com.apple.iokit.IOGraphicsFamily(2.4.1)[A360453D-2050-3C49-A549-AC0DD5E87917]@0xffffff7f8ae0b000->0xffffff7f8ae45fff

dependency: com.apple.iokit.IOPCIFamily(2.9)[F51AA3D6-EC2F-3AD3-A043-06DB79027AA2]@0xffffff7f8a32c000

com.apple.kext.AMD4800Controller(1.4.2)[041E2701-07DD-3EE7-B3D8-29040D924520]@0xffffff7f8c1d8000->0xffffff7f8c356fff

dependency: com.apple.iokit.IOACPIFamily(1.4)[5D7574C3-8E90-3873-BAEB-D979FC215A7D]@0xffffff7f8a9e4000

dependency: com.apple.iokit.IOPCIFamily(2.9)[F51AA3D6-EC2F-3AD3-A043-06DB79027AA2]@0xffffff7f8a32c000

dependency: com.apple.kext.AMDSupport(1.4.2)[B1E391D3-E002-32E9-ACD4-7465DF9CCF7D]@0xffffff7f8c070000

dependency: com.apple.iokit.IOGraphicsFamily(2.4.1)[A360453D-2050-3C49-A549-AC0DD5E87917]@0xffffff7f8ae0b000

com.apple.kext.AMDFramebuffer(1.4.2)[B5E7C9E8-10E9-3757-A18A-23D0FCC1D4B3]@0xffffff7f8c1a3000->0xffffff7f8c1c4fff

dependency: com.apple.iokit.IOACPIFamily(1.4)[5D7574C3-8E90-3873-BAEB-D979FC215A7D]@0xffffff7f8a9e4000

dependency: com.apple.iokit.IOPCIFamily(2.9)[F51AA3D6-EC2F-3AD3-A043-06DB79027AA2]@0xffffff7f8a32c000

dependency: com.apple.kext.AMDSupport(1.4.2)[B1E391D3-E002-32E9-ACD4-7465DF9CCF7D]@0xffffff7f8c070000

dependency: com.apple.iokit.IOGraphicsFamily(2.4.1)[A360453D-2050-3C49-A549-AC0DD5E87917]@0xffffff7f8ae0b000

full crash report

  • I got a faulty displayport-cable to use the iMac screen for a windows through target display mode. My windows machine refused to power up when that cable was plugged into my iMac. Maybe that did it, maybe not. It happened a few times some months ago before I found out the cable was faulty.

According to above info I think it can either be:

  • the gpu (€300 eBay), because the windows pc through target display mode doesn't use the gpu and the problem hasn't occurred yet that way.
  • the motherboard (€200 eBay)
  • the display connector cable? (connecting the motherboard to the lcd). This seems less likely to me but how is it possible that by removing all dust inside the machine can improve the situation if it's a gpu or motherboard problem that doesn't seem to be temp-related? The cable works fine with windows in target display mode, so probably not.
  • ...

I'm ok with replacing one of them but I don't want to spend €500 on a 7,5 years old machine with the possibility replacing both doesn't fix it. Maybe it's not worth trying to fix it and am I better off buying a new one?

Any help is appreciated. Thanks.

Answered! View the answer I have this problem too

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Chosen Solution

The crash report gives a good clue here: AMD4800Controller & AMDFramebuffer

I would suspect the GPU card is bad here. Replacing it would be the best option, the other is to find someone who can reball the GPU chip properly as it's likely the solder joints under the chip have degraded from cooking for a while. The IFIXIT guide I've pointed you to below has the person using their oven to reheat the board (reflowing) while this has a chance of working it really doesn't solve the underlying problem of the bad solder, only getting it to the point of somewhat working. So it's a short lived repair and you'll end up needing to do it again.

This is one system we have had issues in the past and needed to keep clean and had to redo the thermal paste & apply new thermal pads to make sure the system didn't overheat.

I often noted people who play heavy video games or deep graphics work tended to cook their systems. So if you do patch your system up try to not let it overheat. I like using this app: TG Pro to monitor things and it allows you to increase the cooling if you are planning on running the system hard for a duration to help keep it cool.

Here's the IFIXIT video guide you'll need to follow to get it out: iMac Intel 27" EMC 2374, AMD Radeon HD 4850 Video Card Removal & Repair

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Here's a good vid that goes over the difference of reballing Vs reflowing: Linus Attempts BGA Graphics Chip Repair! - Rossmann Repair Group, New York City

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