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
- 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.
Is this a good question?