Apple imac 20 inch early 2008 User Manual
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iMac (20-inch Early 2008) Take Apart — Chassis 2 21 Replace the hard drive fan.11 . Replace the h12. ard driv e. Replace the optical drive flex cable if removed. 13 .
iMac (20-inch Early 2008) Take Apart — Chassis 222 Replace the optical driv14. e. Replace the logic board. 15 . Replace the right speaker16. . Replace the display panel. 17. Replace the front bezel.18. Clean and replace the glass panel19 . . Note: This step is very important. Follow the procedures to ensure the glass is clean and free of particles. Replace the access door. 20.
© 2008 Apple Inc. All rights reserved. Service Source Troubleshooting iMac (20-inch Early 2008)
iMac (20-inch Early 2008) Troubleshooting — General Information 224 General Information Serial Number The serial number for this iMac model is located on the bottom of the computer stand.
iMac (20-inch Early 2008) Troubleshooting — General Information 225 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 or the RAM installed does not • meet the appropriate specifications, 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, 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, try memory that has been verified to work correctly on another system (i.e., “known-good”) or order new memory. Firmware Updates 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 through a software update. Information about firmware versions for Intel Macs can be found in Knowledge Base article 303880 Mac OS X: Firmware Updates for Intel-based Macs. DDR Memory The iMac computer has two SDRAM slots in the bottom of the computer. The iMac ships from the factory with at least 1 or 2 GB MB of DDR2 SDRAM installed, depending on the configuration. The maximum amount of RAM you can install in the iMac is 4 GB total. You can use small-outline dual inline memory modules (SO-DIMMS) of 512 MB, 1 GB, or 2 GB that meet all of these criteria:PC2-5300 • unbuffered• nonparity• 200-pin• 800 MHz DDR2 SDRAM• Note: DIMMs with any of the following features are NOT supported in this iMac:registers or buffers • PLLs• ECC• parity• EDO RAM•
iMac (20-inch Early 2008) Troubleshooting — General Information 226 How to Reset the System Management Controller (SMC) The System Management Controller (SMC) is a chip on the logic board that controls all power functions for your computer. If your computer is experiencing any power issue, resetting the SMC may resolve it. The SMC controls several functions, including:Telling the computer when to turn on, turn off, sleep, wake, idle, and so forth. • Handling system resets from various commands.• Controlling the fans.• Note that resetting the SMC does not reset the PRAM. Resetting the SMC will not resolve issues in which your computer is unresponsive—in these situations, restarting your computer will generally suffice. If your computer isn’t responding, perform these steps one at a time, in this order, until the issue has been resolved: Force Quit (Option-Command-Escape). 1. Restart (Control-Command-Power).2. Force Shut Down (press the power button for 10 seconds).3. Resetting the SMC can resolve some computer issues such as not starting up, not displaying video, sleep issues, fan noise issues, and so forth. If your computer still exhibits these types of issues after you’ve restarted the computer, try resetting the SMC. To reset the SMC on an iMac From the Apple menu, choose Shut Down (or if the computer is not responding, hold the 1. power button for approximately ten seconds until it powers off ). Unplug all cables from the computer, including the power cord. 2. Wait at least 15 seconds. The SMC reset occurs automatically once the iMac has been 3. unplugged from the AC power source for several seconds. Plug the power cord back in, making sure the power button is not being pressed at the time. 4. Reconnect your keyboard and mouse to the computer.5. Press the power button on the back to start up your computer.6. Note: The iMac does not have a button on the main logic board for resetting the SMC, which eliminates the need to remove the computer’s cover to reset it (as required for some other models).
iMac (20-inch Early 2008) Troubleshooting — General Information 227 Diagnostic LEDs The iMac has four built-in diagnostic LEDs on the main logic board that can help you to troubleshoot the computer. The four LEDs are located to the right of the memory slot, under the hard drive data cable. Note: The cable has been removed in this photo. LED #1 Indicates that the trickle voltage from the power supply has been detected by the main • 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 the computer has been shut down or put to sleep. The LED will turn off only if the AC power source is disconnected or the power supply is faulty. LED #2 Indicates that the main logic board has detected proper power from the power supply when • the computer is turned on. This LED will be ON when the computer is turned on and the power supply is 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 display 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 LCD display panel, the LCD display panel or inverter might be installed incorrectly or need replacement.
iMac (20-inch Early 2008) Troubleshooting — General Information 228 Apple Hardware Test (AHT) Error Codes The error codes listed below are the most likely codes that will be generated if a sensor cable is disconnected, dislodged, or if the system has a faulty cable or sensor. Clicking on the link in the chart will show you where the sensor and/or cable connector is located. Or, reference the next two logic board topics which show a picture of the logic board and the sensor locations. AHT ErrorSuspected partSuggested ActionNotes 4SNS/1/40000000:Tp0P Power supply sensor pin/power supply Verify that the single pin connector on the top edge of the power supply is present and securely plugged in. If connector is damaged replace the DC Power Supply cable.If this sensor signal wire is disconnected or faulty the CPU fan will run at full speed. 4SNS/1/40000000:T00P ODD temperature sensor on ODD damaged or cable disconnected from MLB Verify that the sensor cable is securely connected to the MLB and the sensor is properly attached to the ODD mechanism. Replace the sensor if it is damaged.If this sensor is disconnected from the MLB or it is faulty the ODD fan will run at full speed. 4SNS/1/40000000:TA0P Ambient temperature sensor damaged or cable disconnected from MLB Verify that the sensor cable is securely connected to the MLB and the sensor attached to the left speaker housing properly attached. Replace the sensor if it is damaged. 4SNS/1/40000000:TL0P LCD temperature sensor on LCD damaged or cable disconnected from MLB Verify that the LCD sensor cable is securely connected to the MLB and the sensor is attached to the LCD. Replace the sensor if it is damaged.If the sensor is disconnected the CPU fan will run at full speed. 4SNS/1/40000000:TG0H GPU temperature sensor (located on back side of MLB/video card) is disconnected or faulty. Verify that the two pin sensor cable is securely connected to the MLB. The connector is located on the back side of the MLB and requires removal of the MLB to access it. If it continues to fail the diagnostic replace the video card.If the sensor is disconnected the CPU fan will run at full speed.
iMac (20-inch Early 2008) Troubleshooting — General Information 229 AHT ErrorSuspected partSuggested ActionNotes 4SNS/1/40000000:TC0H CPU temperature sensor (located on back side of MLB) is disconnected or faulty. Verify that the two pin sensor cable is securely connected to the MLB. The connector is located on the back side of the MLB and requires removal of the MLB to access it. If it continues to fail the diagnostic replace the logic board.If the sensor is disconnected the CPU fan will run at full speed. 4MOT/1/40000002:ODD Optical drive blower/ fan Verify that the ODD blower/fan cable is securely connected to the MLB and that there are no obstructions that would prevent the blower/fan from rotating. Replace the optical blower/fan if the error continues. 4MOT/1/40000002:HDD Hard drive blower/fan Verify that the hard drive blower/fan cable is securely connected to the MLB and that there are no obstructions that would prevent the blower/fan from rotating. Replace the hard drive blower/fan if the error continues. 4MOT/1/40000002:CPU CPU blower/fan Verify that the CPU blower/fan cable is securely connected to the MLB and that there are no obstructions that would prevent the blower/fan from rotating. Replace the CPU blower/fan if the error continues.
iMac (20-inch Early 2008) Troubleshooting — General Information 230 Logic Board Sensor and Fan Connector Locations, Top Side This is a photo of the top side of the iMac (20-inch Early 2008) logic board showing the sensor and fan connector locations.