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 eort has been made to ensure that the information in this document is accurate. Apple
is not responsible for printing or clerical errors.
Apple
1 Innite 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 Congurations 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 Specications 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: Specic 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: Modied 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 smfeedback2@apple.com
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
2010-09-09
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.
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
congurations
• Ships with and requires at least Mac OS 10.6.3
• Magic Trackpad (CTO)
• Apple Battery Charger (CTO)
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Product Congurations
For product congurations, refer to Apple Support Tech Specs: http://support.apple.com/
specs/
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.
2010-09-09
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.
2010-09-09
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 rst 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 o
to conserve battery life. Press the On/o 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 o.
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Turn on the Trackpad
• To turn the trackpad on, press rmly and release the on/o 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/o button.
iMac (27-inch, Mid 2010) Basics — Overview 16
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/o 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 re, high temperatures, or
water. Don’t charge nonrechargeable AA batteries. Keep batteries out of the reach of children.
2010-09-09
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 ve 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 re, 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 o 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.
2010-09-09
iMac (27-inch, Mid 2010) Basics — Overview 18
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 rmware 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 ash
memory, that will hold the software code indenitely, 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 rmware updates, refer to:
kBase # HT1557: About rmware updates for Intel-based Macs
Troubleshooting Theory
For general information on troubleshooting theory, go to GSX and nd the Service Training
course menu link. From there you can access the Troubleshooting Theory self-paced course.
2010-09-09
iMac (27-inch, Mid 2010) — General Troubleshooting 20
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-specication 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 o.
• The solution to both of these situations is to rst 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 veried 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 xed by
temporarily removing/replacing the backup battery.
2010-09-09
iMac (27-inch, Mid 2010) — General Troubleshooting 21
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
2010-09-09
iMac (27-inch, Mid 2010) — General Troubleshooting 22
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
2010-09-09
iMac (27-inch, Mid 2010) — General Troubleshooting 23
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).
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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 rmware updates.
iMac (27-inch, Mid 2010) — General Troubleshooting 24
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 ows 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 aected 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
specic restore DVD is inserted). If a sensor error is detected, AHT will report an error code containing the aected
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
temperature, or Ambient temp
sensor damaged/disconnected
from logic board.
T00p Excessive Optical Drive area
temperature, or ODD temp
sensor damaged/ disconnected
from logic board.
TH00 Excessive Hard Drive area
temperature, or HDD temp
sensor damaged/disconnected
from logic board. Use the
correct sensor cable, each drive
vendor has a unique sensor
cable model.
Tm0p Excessive logic board
temperature (this sensor is part
of logic board)
Verify that incoming/outgoing air vents
are free from obstruction , that sensor
cable is securely connected to the top
edge of the logic board and attached to
the left speaker housing. Replace sensor
cable if damaged.
Verify sensor cable is securely connected
to the logic board and the sensor
is properly attached to the ODD
mechanism. Replace sensor cable if
damaged.
Verify sensor cable is securely connected
to top left side of logic board and it’s
connected to hard drive. Check for
damaged cable on logic board.
Test with known-good logic board
All fans ramp at full
speed if sensor is
disconnected.
The ODD fan will run
at full speed if sensor is
disconnected.
The HD fan may run at
full speed if the sensor
is disconnected.
2010-09-09
TL0p Excessive LCD panel area
temperature, or LCD temp
sensor damaged/disconnected
from top of logic board
Verify that the LCD sensor cable is
securely connected to the logic board
and the sensor is attached to the LCD.
Replace the sensor cable if damaged
iMac (27-inch, Mid 2010) — General Troubleshooting 25
The CPU fan will run at
full speed if the sensor
is disconnected.
TS2P Excessive upper internal
enclosure temperature, or
Skin temp sensor damaged/
disconnected from top of logic
board.
Verify that the skin temp sensor cable
is securely connected to the top of the
logic board and sensor is attached to
rear housing (near the camera). Replace
the sensor cable if damaged.
TC0H Excessive processor heatsink
temperature, or CPU temp
sensor damaged/disconnected
from back side of logic board
(this sensor is part of logic
board)
TG0D Excessive graphics processor
die temperature (this sensor
is part of graphics processor
chip)
TG0H Excessive graphics processor
heatsink temperature, or
GPU temp sensor damaged/
disconnected from back side of
logic board (this sensor is part
of video card assembly)
Tp1P, Tp2H,
Tp3H
Excessive power supply
temperature (these sensors
are part of the power supply
board)
ODD fan Optical fan/blower located
next to right speaker
HDD fan Hard drive fan/blower, located
below logic board, near hard
drive
CPU fan CPU fan/blower, located next
to left speaker (logic board has
to be removed to replace CPU
blower)
Check CPU sensor cable connection to
logic board. It requires removal of the
logic board.
Test with known-good video card
Check GPU sensor cable connection to
logic board. It requires removal of the
logic board.
Test with known-good power cable
harness , or known-good power supply
board.
Verify that the ODD blower/fan cable is
securely connected to the right side of
the logic board and that there are no
obstructions that would prevent the
blower/fan from rotating. Replace fan if
the error continues.
Verify that the HDD blower/fan cable
is securely connected to the top of
the logic board and that there are no
obstructions that would prevent the
blower/fan from rotating. Replace fan if
the error continues.
Verify that the CPU blower/fan cable is
securely connected to the left side of
the logic board and that there are no
obstructions that would prevent the
blower/fan from rotating. Replace fan if
the error continues.
If the sensor is
disconnected, the
CPU fan will run at full
speed.
If sensor is
disconnected the CPU
fan will run at full
speed.
Normal fan operation,
except the ODD blower
Normal fan operation,
except the HDD blower
Normal fan operation,
except the CPU blower
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iMac (27-inch, Mid 2010) — General Troubleshooting 26
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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iMac (27-inch, Mid 2010) — General Troubleshooting 27
Sensor Connector Location: Back Side of Logic Board
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iMac (27-inch, Mid 2010) — General Troubleshooting 28
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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iMac (27-inch, Mid 2010) — General Troubleshooting 29
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.
2010-09-09
iMac (27-inch, Mid 2010) — General Troubleshooting 30
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