Apple iMac 27 mid 2010 Service Manual

Apple Technician Guide

iMac (27-inch, Mid 2010)

2010-09-09

Apple Inc.

© 2010 Apple Inc. All rights reserved.

Under the copyright laws, this document may not be copied, in whole or in part, without the written consent of Apple.

Every effort has been made to ensure that the information in this document is accurate. Apple is not responsible for printing or clerical errors.

Apple

1 Infinite Loop Cupertino, CA 95014-2084 USA

+ 1 408 996 1010 www.apple.com

Apple, the Apple logo, Mac, and Macintosh are trademarks of Apple Inc., registered in the U.S. and other countries.

iMac (27-inch, Mid 2010)

Contents

About This Guide

Updates  10

Updated 9 September 2010  10 Updated 9 August 2010  10

Apple Technician Guide introduced 27 July 2010  10

Feedback  10

Basics

Overview  12

Identifying Features   13
Product Configurations		13
Safety Precautions	14
Serial Number Location		15
New Accessories	16
Magic Trackpad	16
Apple Battery Charger		18

Troubleshooting

General Troubleshooting		20
Wireless Troubleshooting		20
Update System Software & Firmware  20
Troubleshooting Theory	20
Hardware vs. Software	21
Common Reset Procedures  21
Power On Self Test (POST)		21
Resetting the System Management Controller (SMC)  22
Resetting Parameter RAM (PRAM)  22
Starting Up in Safe Mode		23

Removing the Battery, Measuring DC Voltage  24

Diagnostics  25

Sensors Errors  25

Sensor Locations  27

Diagnostic LEDs  29

Location of Diagnostic LEDs  29

LED Functions	30
LED Startup Sequence		31
Logic Board Test Points		32
Functional Overview  33
Block Diagram	34

Symptom Charts  35

Startup and Power  35

No Power, Dead Unit  35 Won’t Start Up  37 Intermittent Shutdown  39

Kernel Panic, System Crashes  44 No Video  46

Corrupted Video  48

Burnt Smell/Odor  51 Uncategorized Symptoms  52

Display  53

Backlight Issue/No Backlight  53

Noise / Unstable Flickering  55 LCD Image Issues  58 Incorrect/Missing Colors  60 Distorted/Blurred Image  62 Pixel Anomalies  64 Vertical/Horizontal Lines  66

Non-Uniform Brightness / Color  68 Cosmetic Defects  69 Uncategorized Symptoms  69

Mass Storage  70

Hard Drive Not Recognized  70

Optical Drive Not Recognized  76

Optical Drive Won’t Accept/Eject Media  77 Optical Drive Read/Write Error  78

Optical Drive Not Performing to Specifications  80 Optical Drive Noisy  82

SD Card Will Not Insert Into Slot  83 SD Card Not Recognized  84 Uncategorized Symptoms  85

Communications  86

AirPort/Bluetooth Issues  86

AirPort Card Kernel Panic  89

Ethernet Port/Device Issue  90 Wireless Input Device Does Not Pair  91 Uncategorized Symptoms  93

Input/Output Devices  94

Apple Remote Inoperable  94

Audio:Microphone  96

Audio:Built-in Speakers Have Distorted Sound			97
Audio:No Audio from Built-in Speakers		98
Camera Issues  101
FireWire Device Not Recognized  102
USB Device Not Recognized	104
Wired Keyboard Does Not Function Properly			106
Keyboard:Specific Keys Do Not Respond		108
Wired Keyboard/Mouse Not Recognized		108
Wireless Input Device Does Not Pair   110
Apple Wireless Mouse/Magic Trackpad Erratic Tracking  113
Wireless Input Device Loses Connection		114
Apple Battery Charger Does Not Charge Batteries   116
Mechanical  118
Noise/Hum/Vibration  118
Fan Failures / Thermal Issues	121
Stand/Hinge Issues  122
Physical Damage  123
Uncategorized Symptoms  123

Take Apart

General Information	125
Opening the Unit  125
Required Tools   125
Required Special Tools for Glass Panel		126
Cleaning Tools Starter Kit  126
Cleaning & Handling the Glass Panel		127
Do’s and Don’ts  127
Handling a Broken Glass Panel  128
How to Remove a Broken Glass Panel		128
Safety  133
Logic Board Handling  134
Reassembly Steps	134

Note About Images in This Manual  134

Screw Sizes  134

Access Door  135

Memory  137

Removal  138

Reassembly  138

Glass Panel  139

Removal  140

Reassembly  141

Camera  144

Removal  145

Reassembly  146

LCD Panel	147
Removal	148
Handling the Panel				153
Reassembly		154
Vertical Sync Cable (Vsync)  157
LED Temp Sensor Cable					158
DisplayPort Cable			159
Audio Ports and Cable					161
AirPort Antenna			163
AirPort Card		165
AirPort Carrier Board				167
AirPort Cable		169
Bluetooth Antenna  171
Bluetooth Board			173
LED Backlight Board				175
Power Supply		177
Removal	178
Reassembly		179
Backlight Pressure Wall					180

Power Supply/Hard drive Pressure Wall  182

Removal  183

Reassembly  183

Hard Drive  185

Removal  186

Reassembly  187

Hard Drive Sensor Cable  188

Removal  189

Reassembly  189

Optical Drive  190

Removal  191

Reassembly  193

Optical Sensor Cable  195

Optical Drive Fan  197

SD Card Reader  199

Removal  200

Reassembly  201

SD Card Reader Cable  202

IR Board and Cable  204

Logic Board  206

Removal	207
Handling the Logic Board  209
Reassembly		210
Video Card	216
Solid State Drive (SSD)  219
Removal	220
Reassembly		222

SSD Data Cable  223

Optical/MXM Pressure Wall  225

Hard Drive Data Cable  227

Optical Drive Data Cable  230

Battery  232

Removal  233

Reassembly  233

Right Speaker  234

CPU Fan  236

Removal  237

Reassembly  238

Ambient Temp Sensor  239

Removal  240

Reassembly  240

Left Speaker  241

Removal  242

Reassembly   242

Hard Drive Fan  244

Mechanism Cover  246

Stand  248

Removal  249

Reassembly  250

Mechanism  252

Bluetooth Cable  254

Camera Cable  257

Cable, AC/DC Power/Backlight/SATA  260

Cable, AC/DC Power/Backlight/SATA, SSD  262

Microphone Cable  265

Rear Housing  266

Reassembly  267

Additional Procedures

Retrieving Mechanism  272

Views

Exploded Views  277

Exploded View #1  277

Exploded View #2  278

Exploded View #3  279

External Views  280

Rear View  280

Ports  281

Internal Views  282

Photo of Components below LCD  282

Photo of Components in the Rear Housing  283

Logic Board, Front Side	284
Logic Board, Back Side	285

Screw Chart  286

Apple Technician Guide

About This Guide

iMac (27-inch, Mid 2010)

© 2009 Apple Inc. All rights reserved.

Updates

Updated 9 September 2010

Troubleshooting:

•Display:several symptoms:Modified steps to allow unit to warm up for about a minute (instead of 15 minutes) before evaluating front-of-screen performance.

Take Apart:

•LCD Panel:Added note that overtightening screws could lead to issue of light leakage after unit is reassembled.

•Camera and Rear Housing:Added note that white thermal paste intended for camera should not be used for any other purpose (such as portable computer heatsinks).

Updated 9 August 2010

•Basics:Overview:New Accessories:Magic Trackpad and Apple Battery Charger:Added links to the User Guides:

Apple Technician Guide introduced 27 July 2010

Feedback

We want your feedback to help improve this and future Technician Guides! Please email any comments to [e-mail]

2010-09-09

iMac (27-inch, Mid 2010) About This Guide — Updates  10

Apple Technician Guide

Basics

iMac (27-inch, Mid 2010)

© 2010 Apple Inc. All rights reserved.

Overview

Introducing the iMac (27-inch, Mid 2010) with the latest Intel Core i3, Core i5 and Core i7 processors and powerful new graphics.The new iMac line is the fastest ever with dual-core processor speeds up to 3.6 GHz, quad-core speeds up to 2.93 GHz and discrete graphics including the powerful ATI Radeon HD 5750.

The processors feature an integrated memory controller to access the system memory directly, allowing the new iMac to take full advantage of its faster 1333 MHz memory. New discrete ATI Radeon HD processors deliver incredibly smooth, crisp graphics for the most demanding 3D games, creative software and technical applications. Refer to the next page for more features.

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iMac (27-inch, Mid 2010) Basics — Overview  12

Identifying Features

The iMac (27-inch, Late 2010) computer features include:

•27-inch display 2560 x 1440 LED-backlit display

•Increased processor speeds:

•3.20 GHz Intel Core i3 with 4MB shared L3 cache

•2.80 GHz Intel Core i5 (CTO)

•3.60 GHz Quad-Core Intel Core i5 with 8MB shared L3 cache

•2.93 GHz Quad-Core Intel Core i7 (CTO)

•4 GB 1333 MHz DDR3 SDRAM expandable up to 16GB

•Main memory PC3-10600, DDR3 (1333), 204-pin, ships with 2x1333 MHz SO-DIMMs

•SD card reader slot with SDXC (Secure Digital Extended Capacity) supports 32GB - 2TB

•Mini DisplayPort output (DVI,VGA, and dual-link DVI) and supports input from external DisplayPort sources (adapters sold separately)

•Graphics and video support:

•AMD Radeon HD 5670 graphics processor with 512MB GDDR3

•AMD Radeon HD 5750 graphics processor with 1 GB GDDR5

•Hard drive:1TB, 2TB

•Solid State Drive options:

•256GB SSD (SSD only, without a hard drive)

•256GB SSD + 1TB Serial ATA Hard Drive (CTO)

•256GB SSD + 2TB Serial ATA Hard Drive (CTO)

•Magic Mouse (Mid 2010) and Apple Wireless Keyboard (2009), standard with all configurations

•Ships with and requires at least Mac OS 10.6.3

•Magic Trackpad (CTO)

•Apple Battery Charger (CTO)

Product Configurations

For product configurations, refer to Apple Support Tech Specs:http://support.apple.com/ specs/

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iMac (27-inch, Mid 2010) Basics — Overview  13

Safety Precautions

WARNING: HIGH VOLTAGE:The AC/DC power supply PCB remains powered up whenever the system is plugged in, whether or not the system has been turned on. Use extreme caution when troubleshooting the system with the front bezel removed.

Important: If the computer is shut down by removing the power cord, allow the power supply a good 2-3 minutes to discharge the capacitors before handling it. However, if you select“Shut Down”via the Apple menu, the computer will discharge the power supply capacitor almost immediately.

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iMac (27-inch, Mid 2010) Basics — Overview  14

Serial Number Location

The iMac (27-inch, Mid 2010) serial number is located on the base of the stand.When replacing a stand, transfer the serial number to the new stand.

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iMac (27-inch, Mid 2010) Basics — Overview  15

New Accessories

Magic Trackpad

The wireless Magic Trackpad uses Bluetooth® technology to connect to the Mac and comes with two AA batteries installed.To use the Magic Trackpad and its full features, update your Mac to Mac OS X version 10.6.4 or later, and then install the latest trackpad software using Software Update, if needed. Refer to the Magic Trackpad Quick Start Guide for more information.

Note:If for some reason the iMac (27-inch, Mid 2010) needs the system software reinstalled, pair the Magic Trackpad and then run Software Update. If for some reason you notice that only basic functionality is present on the Magic Trackpad, ensure that it’s paired correctly before launching Software Update. Refer to the following Kbase articles for more information.

•HT4273 About Magic Trackpad Update 1.0 for Windows

•HT4254 About Magic Trackpad and Multi-Touch Trackpad Update 1.0

About the Indicator Light

The indicator light displays the status of your Magic Trackpad and the batteries.

•When you first turn your trackpad on, the indicator light glows steadily for 2 to 3 seconds, indicating the batteries are good.

•If your trackpad isn’t paired with a Mac, the light blinks, indicating your trackpad is in discovery mode and ready to pair (pairing means connecting your trackpad and Mac to each other wirelessly).

•If you don’t pair your trackpad with your Mac within 3 minutes, the light and trackpad turn off to conserve battery life. Press the On/off button on your trackpad to turn it on again, allowing you to pair it with your Mac.

•When your trackpad is on and connected, the indicator light turns off.

Turn on the Trackpad

•To turn the trackpad on, press firmly and release the on/off button.

•To turn on the trackpad and make it stay in discovery mode (prevent auto-pairing to previous known host), press and hold the on/off button.

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Pairing the Magic Trackpad

To pair your trackpad:

1.Choose Apple ( ) > System Preferences, and then click Trackpad.

2.Click“Set Up Bluetooth Trackpad …”in the lower-right corner.

3.Press the On/off button on your trackpad to turn it on.

4.Click Continue when your trackpad is detected.

Once your trackpad is paired with your Mac, use Software Update again to make sure you have the latest software installed.

Note:If the iMac (27-inch, Mid 2010) needs to have system software reinstalled for some reason, pair the Magic Trackpad and then run Software Update. If for some reason you notice that only basic functionality is present on the Magic Trackpad, ensure that it’s paired correctly before launching Software Update.

Installing Batteries

1.Use a coin to remove the battery compartment cover on the left side.

2.Insert batteries into the battery compartment as shown.

Warning:Replace or recharge batteries at the same time. Don’t mix old batteries with new batteries and don’t mix battery types (for example, alkaline and lithium batteries). Don’t open or puncture the batteries, install them backwards, or expose them to fire, high temperatures, or water. Don’t charge nonrechargeable AA batteries. Keep batteries out of the reach of children.

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iMac (27-inch, Mid 2010) Basics — Overview  17

Apple Battery Charger

Use the Apple Battery Charger to charge rechargeable NiMH batteries for your Apple products that use AA batteries. Each Apple Battery Charger comes with six high-performance AA NiMH batteries:two for your keyboard, two for your mouse or trackpad, and two for charging.You can use the Apple Battery Charger to charge either one or two NiMH rechargeable batteries.To charge batteries fully, allow at least five hours of charging time. For more information, refer to the Battery Charger Quick Start and/or Kbase article HT 4275 About Apple Battery Charger.

Batteries

Use only NiMH rechargeable batteries in the Apple Battery Charger. Don’t try to charge nonrechargeable AA batteries (lithium or alkaline) in the charger.

Caution:Risk of explosion if battery is replaced by an incorrect type. Dispose of used batteries according to the instructions. Don’t open or puncture the batteries, install them backwards, short circuit, or expose them to fire, high temperatures, or water. Keep batteries out of the reach of children.

Status Lights

The indicator light on top of the Apple Battery Charger displays the charging status of the batteries.

•Amber:The batteries are charging.

•Green:The batteries are charged and ready to use—the green indicator light shuts off after six hours

•No light:May indicate any of the following conditions:

•The batteries are charged and ready to use.

•The inserted batteries are too deeply discharged to register immediately.

•Flashing Amber:May indicate any of the following conditions:

•The batteries haven’t been properly installed in the charger.

•An unsupported type of battery is in the charger.

•The batteries may be faulty or damaged and should be replaced.

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Apple Technician Guide

Troubleshooting

iMac (27-inch, Mid 2010)

© 2010 Apple Inc. All rights reserved.

General Troubleshooting

Wireless Troubleshooting

If you’re having issues with Bluetooth and wireless connectivity issues, refer to the following:

•TS3048 Troubleshooting wireless mouse and keyboard issues

•HT3887 Wireless input devices: Bluetooth frequently asked questions

•HT1365 AirPort and Bluetooth: Potential sources of interference for wireless devices and networks

•HT3903 Apple Wireless Keyboard and Mouse: How to install batteries

•HT4273 About Apple Magic Trackpad Update 1.0 for Windows

•HT4254 About: Magic Trackpad and Multi-Touch Trackpad Update 1.0

•HT 4275 About Apple Battery Charger

•Bluetooth Service Diagnostic (BSD) self-paced training

•Bluetooth Troubleshooting Course

Update System Software & Firmware

Important: Ensure the correct version Mac OS X and latest software and firmware updates have been applied before you begin troubleshooting. Computers sometimes exhibit symptoms that indicate the wrong Mac OS X system software is installed.

Firmware is the name given to software that is written into memory circuits such as flash memory, that will hold the software code indefinitely, even when power is removed from the hardware. Firmware on Intel Mac computers is designed to be updated if necessary by

running the Mac OS X Software Update check (available in the Apple menu) while computer is connected to the Internet. For more information about firmware updates, refer to:

kBase # HT1557: About firmware updates for Intel-based Macs

Troubleshooting Theory

For general information on troubleshooting theory, go to GSX and fiind the Service Training course menu link. From there you can access the Troubleshooting Theory self-paced course.

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Hardware vs. Software

For information on how to isolate a hardware issue from a software issue, refer to: kBase #TS1388: Isolating issues in Mac OS X

For information on how to troubleshoot a software issue, refer to: kBase #HT1199: Mac OS X: How to troubleshoot a software issue

kBase #TS1394: Mac OS X:Troubleshooting installation and software updates kBase #HT2956:Troubleshooting Mac OS X installation from CD or DVD

Common Reset Procedures

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 the incorrect type of RAM, poor connection, 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 the tones until the computer is turned off.

•The solution to both of these situations is to first re-seat the memory and test the computer again. If the memory fails the POST test again, remove all installed memory and test by installing one by one each memory that has been verified to work correctly on another system (i.e.,“known-good”) 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.

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Resetting the System Management Controller (SMC)

The System Management Controller (SMC) is a chip on logic board that controls all power functions. If computer is experiencing any power issue, such as not starting up, not displaying video, sleep issues, battery management, or fan noise issues, resetting SMC may resolve it.To reset SMC on an iMac:

1.Shut down the computer.

2.Unplug all cables from computer, including power cord.

3.Press and hold the power button for 5 seconds.

4.Release the power button.

5.Attach the computer’s power cable.

Note:If you press the power button while inserting the power cord, the iMac will enter a mode in which the fans run at full speed. For more information, refer to kbase article TS1433:iMac: Fans run at full speed after computer turns on

6.Press the power button to turn on the computer.

For more information, refer to:

kBase #HT3964: Intel-based iMac: How to reset the System Management Controller

Resetting Parameter RAM (PRAM)

PRAM stores certain system and device settings in a location that Mac 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, P, and R.You will need to hold these keys down simultaneously in Step 4.

Note:If the keyboard does not have an Option key, use the Alt key instead.

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.

For more information, refer to:

kBase #HT1242: Mac OS X:What’s stored in PRAM kBase #HT1379: Resetting your Mac’s PRAM and NVRAM

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Starting Up in Safe Mode

A Safe Boot is a special way to start Mac OS X when troubleshooting.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). During startup, ”Safe Boot”appears on the Mac OS X startup screen and a gray progress bar is displayed on bottom of window (since Mac OS X 10.6).

5.To leave Safe Mode, restart computer normally, without holding down any keys during startup.

For more information, refer to:

kBase #HT1564: Mac OS X:What is Safe Boot, Safe Mode? kBase #TS1884: Safe Boot takes longer than normal startup

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Removing the Battery, Measuring DC Voltage

1.Unplug the computer. Allow several minutes for power supply to discharge.

2.Remove logic board.

3.Remove coin battery for 1-2 minutes.The coin battery is located on the back side of the logic board (see graphic below).

4.Measure DC voltage on battery touching battery with red probe, and grounding with black probe. If voltage is 2.7v or less, replace battery.

5.Reinstall the battery and logic board.This will reset the logic board.

6.Power on computer.

7.If computer boots, check for and install all software and firmware updates.

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Diagnostics

The following diagnostics are required for this product:

•Apple Service Diagnostic (ASD), version 3S140

•For iMac (27-inch, Mid 2010):Apple Hardware Test (AHT), version 3A202

•Bluetooth Service Diagnostic (BSD) 1.1

Sensors Errors

Run latest available service utilities to determine if any thermal sensors or blowers are malfunctioning.When a test reports an error, reseat appropriate connections and check that all air flows are free from obstruction. If issue persists, replace the corresponding part (sensor, blower, logic board, video card, or power supply). See chart below for correlation between affected sensor, sensor location, and additional checks to perform.

Note:AHT can be run by pressing the D key on startup (if hard drive was not reformatted, or if adequate system specific restore DVD is inserted). If a sensor error is detected, AHT will report an error code containing the affected sensor name (ex:“4SNS/1/40000000 TC0H”error code reports to sensor TC0H).

Sensor	Suspected part and Location	Suggested Action	Notes
TA0P	Excessive incoming Ambient air	Verify that incoming/outgoing air vents	All fans ramp at full
	temperature, or Ambient temp	are free from obstruction , that sensor	speed if sensor is
	sensor damaged/disconnected	cable is securely connected to the top	disconnected.
	from logic board.	edge of the logic board and attached to
		the left speaker housing. Replace sensor
		cable if damaged.
T00p	Excessive Optical Drive area	Verify sensor cable is securely connected	The ODD fan will run
	temperature, or ODD temp	to the logic board and the sensor	at full speed if sensor is
	sensor damaged/ disconnected	is properly attached to the ODD	disconnected.
	from logic board.	mechanism. Replace sensor cable if
		damaged.
TH00	Excessive Hard Drive area	Verify sensor cable is securely connected	The HD fan may run at
	temperature, or HDD temp	to top left side of logic board and it’s	full speed if the sensor
	sensor damaged/disconnected	connected to hard drive. Check for	is disconnected.
	from logic board. Use the	damaged cable on logic board.
	correct sensor cable, each drive
	vendor has a unique sensor
	cable model.
Tm0p	Excessive logic board	Test with known-good logic board
	temperature (this sensor is part
	of logic board)
TL0p	Excessive LCD panel area	Verify that the LCD sensor cable is	The CPU fan will run at
	temperature, or LCD temp	securely connected to the logic board	full speed if the sensor
	sensor damaged/disconnected	and the sensor is attached to the LCD.	is disconnected.
	from top of logic board	Replace the sensor cable if damaged

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TS2P	Excessive upper internal	Verify that the skin temp sensor cable
	enclosure temperature, or	is securely connected to the top of the
	Skin temp sensor damaged/	logic board and sensor is attached to
	disconnected from top of logic	rear housing (near the camera). Replace
	board.	the sensor cable if damaged.
TC0H	Excessive processor heatsink	Check CPU sensor cable connection to	If the sensor is
	temperature, or CPU temp	logic board. It requires removal of the	disconnected, the
	sensor damaged/disconnected	logic board.	CPU fan will run at full
	from back side of logic board		speed.
	(this sensor is part of logic
	board)
TG0D	Excessive graphics processor	Test with known-good video card
	die temperature (this sensor
	is part of graphics processor
	chip)
TG0H	Excessive graphics processor	Check GPU sensor cable connection to	If sensor is
	heatsink temperature, or	logic board. It requires removal of the	disconnected the CPU
	GPU temp sensor damaged/	logic board.	fan will run at full
	disconnected from back side of		speed.
	logic board (this sensor is part
	of video card assembly)
Tp1P,Tp2H,	Excessive power supply	Test with known-good power cable
Tp3H	temperature (these sensors	harness , or known-good power supply
	are part of the power supply	board.
	board)
ODD fan	Optical fan/blower located	Verify that the ODD blower/fan cable is	Normal fan operation,
	next to right speaker	securely connected to the right side of	except the ODD blower
		the logic board and that there are no
		obstructions that would prevent the
		blower/fan from rotating. Replace fan if
		the error continues.
HDD fan	Hard drive fan/blower, located	Verify that the HDD blower/fan cable	Normal fan operation,
	below logic board, near hard	is securely connected to the top of	except the HDD blower
	drive	the logic board and that there are no
		obstructions that would prevent the
		blower/fan from rotating. Replace fan if
		the error continues.
CPU fan	CPU fan/blower, located next	Verify that the CPU blower/fan cable is	Normal fan operation,
	to left speaker (logic board has	securely connected to the left side of	except the CPU blower
	to be removed to replace CPU	the logic board and that there are no
	blower)	obstructions that would prevent the
		blower/fan from rotating. Replace fan if
		the error continues.

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Sensor Locations

Temp sensors and fan connector locations are shown in the next two graphics. Ensure cables are correctly routed and the sensors and fans are properly connected. If a sensor or fan is faulty or not connected, Apple Hardware Test will generate an error code.

Sensor Connector Locations:Top Side of Logic Board

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Sensor Connector Location: Back Side of Logic Board

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Diagnostic LEDs

The iMac (27-inch, Mid 2010) computer has four built-in diagnostic LEDs on the main logic board that can help you to troubleshoot the computer.The LEDs are located on the bottom left edge of the logic board (under a piece of black mylar tape) and can only be seen when looking through the lower vents of the enclosure. Refer to the next page for a close up graphic of the troubleshooting LEDs.

Location of Diagnostic LEDs

The LEDs are located under the mylar tape, on the bottom, left corner of the logic board.They can only be seen when looking through lower vents of rear housing

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LED Functions

LED #1

•Indicates that trickle voltage from power supply has been detected by logic board.This LED will remain ON whenever the iMac is connected to a working AC power source.The LED will remain ON even when computer has been shut down or put to sleep.The LED will remain OFF only if the AC power source is missing or disconnected , if the logic board is disconnected from the power supply, or if the power supply board is faulty.

LED #2

•Indicates that the main logic board has detected proper power from the power supply when the computer is turned on and that logic board voltage regulators are functioning properly.This LED will be ON when the computer is turned on and the power supply should be working correctly.

LED #3

•Indicates that the computer and the video card are communicating.This LED will be ON when the computer is communicating properly with the video card. If LEDs 1 and 2 are ON and you heard the startup sound, but LED 3 is OFF, then the video card might be installed incorrectly or need replacement.

LED #4

•Indicates that the computer and the LCD panel are communicating.This LED will be ON when the computer is turned on and video signal is being generated. If the LED is ON and there is no image on the display, then the LCD panel, the LED backlight board, or the cables between might be installed incorrectly or need replacement.

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