@mod_builder you are not telling us if besides the chime coming on if it gives you any other indication of coming to life. Ultimately you know you will have to remove disassemble your iMac to see what is going on with it. iMac Intel 27" EMC 2429
Let us know if you hear anything like this:
No Startup
• No startup sound or POST (Power On Self-Test)
• Gray screen appears during startup
• Some video activity, Apple logo, spinning gear
• Prohibitory sign or folder with a flashing question mark
• Startup chime or error beep tones
• Audible fan, hard drive spin or optical drive reset sounds
• Sleep LED on, blinking or went out.
• Caps Lock LED on wired keyboard toggles on and off when pressed
Power On Self Test (POST)
Intel-based Mac computers such as the iMac rely on a combination of tones and blinking LEDs to display Power On Self Test (POST) error codes.
• If the computer detects out-of-specification or no SDRAM, the screen will remain black but the computer will beep. This error condition may be due to physically damaged RAM, installing an incorrect type of RAM, or not having RAM installed.
• Some RAM may appear to pass the Power-On-Self-Test (POST) but still cannot be used by the operating system. In this case, the computer will display a gray screen, sound three tones and repeat tones until computer is turned off.
• The solution to both of these situations is to first re-seat memory and test computer again. If memory fails POST again, remove all installed memory and test by installing one by one each memory module that has been verified to work correctly on another computer (i.e.,“known-good” memory) or order new memory.
• A sequence of tones heard at startup or a no video symptom may also be fixed by temporarily removing/replacing the backup battery.
Starting Up in Safe Mode
A Safe Boot is a special way to start OS X when troubleshooting. Starting up into Safe Mode does several things that can help resolve software or directory issues that may exist on the startup volume. To start up in Safe Mode:
1. Make sure computer is shut down.
2. Press power button.
3. Immediately after you hear the startup tone, press and hold Shift key.
Note: The Shift key should be held as soon as possible after startup tone but not before.
4. Release Shift key when you see the screen with the gray Apple and progress indicator (looks like a spinning gear). Note that booting into Safe Mode will take longer than a normal startup. During startup, the words ”Safe Boot” appear on the OS X startup screen and a gray progress bar is displayed on bottom of window (since OS X 10.6).
5. To leave Safe Mode, restart computer normally, without holding down any keys during startup.
Resetting Parameter RAM (PRAM)
PRAM stores certain system and device settings in a location that OS X can access quickly.
Exactly which settings are stored in the computer’s PRAM varies depending on the type of computer as well as the types of devices and drives connected. To reset PRAM:
1. Shut down the computer.
2. Locate the following keys on keyboard: Command, Option (Alt), P, and R. You will need to hold these keys down simultaneously in Step 4.
3. Press power button.
4. Immediately press and hold Command-Option-P-R keys.
Important: You must press this key combination before the gray screen appears.
5. Hold down keys until the computer restarts, and you hear the startup chime a second time.
6. Release keys.
Let us know what your LED’s are showing
Diagnostic LEDs
The iMac (27-inch, Mid 2011) computer has four built-in diagnostic LEDs on the main logic board that can help you to troubleshoot the computer. The LEDs are located above the speaker connectors and slightly to the left.
LED #1
• Indicates that the trickle voltage from power supply has been detected by main logic board.
This LED will turn ON when you connect the iMac to a working AC power source. The LED will remain ON as long as the computer is ON or asleep.
• When computer has been correctly shutdown, the LED#1 behavior may differ:
• - If a startup event is scheduled in System Preferences/Energy saver, LED#1 will stay ON after a correct shutdown,
• - If no startup event is scheduled in System Preferences/Energy saver, LED#1 will turn OFF and will stay OFF as long as power cord is kept connected and AC power source is present.
Disconnecting the power cord and plugging it back will turn back this LED ON , even if computer is still off.
• After disconnecting and reconnecting the AC power source, this LED could remain OFF if the AC power source is missing or disconnected , if the logic board is disconnected from the power supply or from the AC receptacle, or if the power supply board is faulty.
LED #2
• Indicates that computer is turned on. This LED will be ON as long as computer is turned on (but is not asleep) and power supply and voltage regulators are working correctly.
LED #3
• Indicates that computer and video card are communicating. This LED will be ON when computer is communicating properly with video card. If LEDs 1 and 2 are ON and you heard the startup sound, but LED 3 is OFF, then the backup battery (on back of logic board) may need to be reseated, or the video card might be installed incorrectly or needs replacement.
LED #4
• Indicates that computer and LCD panel are communicating. This LED will be ON when computer is turned on and video signal is being generated. If LED#4 is ON and there is no image on display, then the LCD panel, the LED backlight board, or the cables between LCD and logic board or backlight board might be installed incorrectly, or need replacement.
LED Startup Sequence
LED #1 = Power available.
If no LED is visible:
• First disconnect the power cord from computer, then reconnect it to reset the LED status, in case computer was correctly shutdown and AC was kept connected since
• Verify AC source
• Verify known-good power cord is connected
• Verify cable connection between AC inlet and power supply
• Verify cable connection between power supply and logic board
• Verify power supply
LED #1 + LED #2 = Power available, and system is powered on.
If second LED is not visible when power button is pressed:
• Verify power button connection to logic board
• Verify power button functionality
• Verify cable connection between power supply and logic board
• Verify power supply
• Verify logic board
LED #1 + LED #2 + LED #3 = Power available, system is powered on, and video card found.
If third LED is not visible after power on:
• Verify that the MXM video card is seated properly
• Verify if boot chime is present and fans are running when powered ON (reset SMC and
PRAM, reseat or check backup battery if necessary for proper boot up):
If POST boot chime is not heard, go to No Startup symptom flow,
If POST boot chime is heard, go to No Video symptom flow.
LED #1 + LED #2 + LED #3 + LED #4 = Power available, system is powered on, video card
found, and internal LCD found.
If fourth LED is not visible after power on:
• Verify internal DisplayPort cable connections between LCD panel and logic board
• Inspect LCD display cables for cable damage
• Verify external video functionality, and according to result check the following items:
If external display works then verify/replace the LED backlight board
If external display works then verify/replace the LCD panel
If external display does not work verify/replace the logic board
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