How can I verify which part is bad based on LEDs?
iMac 3.06 GHz 24" EMC 2267 with the 4850 HD.
Note: My issues started right after installing Mavericks.
- iMac won't start up, often without the LCD coming on
- No startup chime.
- Screen intermittently will come on if I leave the computer unplugged long enough before trying to start up again.
- When the screen does come on it will show the Apple logo and then briefly show the "rotating" startup symbol.
- Screen flashes with some horizontal line artifacts before going off.
I took the iMac bezel off and observed the diagnostic LEDs. There are two different scenarios for the LEDs.
- If the screen comes on, all 4 LEDs light up.
- If the screen does not come on, only the first 2 LEDs light up.
Regardless of LEDs the computer does not chime or fully start up.
I have tried to start up in Target Disk Mode, but only had limited success one time. That one time I was able to get the root directory listing on the drives, but I could not open any directories.
I have tried to start up using external Time Machine drive by holding option at startup with no change in behavior.
I tried changing the RAM to no effect. I took the RAM out and it did the beeps to indicate no RAM was installed.
Based on what I've read, this means either the logic board, video card, or LCD could be faulty. How am I to figure out which one it is? I want to think that if it were the LCD then I should still be able to start into target disk mode. Am I wrong?
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