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Apple imac 20 inch early 2008 User Manual

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    							iMac (20-inch Early 2008) Troubleshooting — General Information 2 31
    Logic Board Sensor Locations, Back Side
    This is a photo of the back side of the iMac (20-inch Early 2008) logic board showing the GPU and 
    CPU sensor connector locations.
    Cleaning Tools for the LCD and Glass
    The following tools are necessary when servicing this product. Order a cleaning kit, (076-1277), 
    which contains all the items listed, or purchase the tools individually.Suction cups, one pair (922-8252)
    • 
    Sticky silicone roller (6-inch) to clean the glass panel, Qty. of one (922-8261)• 
    Sticky sheets to clean the silicone roller, Qty of 2 pads (922-8262)• 
    Polishing cloths, clean, anti-static, micro fiber “terry” style cloth, Qty. 5 cloths, (922-8263)• 
    Gloves, lint-free, anti-static, Qty. of two (922-8253)• 
    Microfoam bag to store the glass panel, Qty. of one (5 bags) 922-8259)• 
    ESD bag for LCD display storage, Qty. of one (5 bags) (922-8258)• 
    ESD bag for LCD display storage (922-8258)•  
    						
    							iMac (20-inch Early 2008) Troubleshooting — General Information 232
    LensPen Cleaning Tool
    LENSPEN products are simple to use and are effective at removing smudges and fingerprints on 
    the inside/outside of the glass panel. The two LENSPEN products that have been tested on the 
    iMac are shown below, the VidiMax and the LapTop-Pro. Refer to www.lenspen.com for more 
    information. 
    						
    							iMac (20-inch Early 2008) Troubleshooting — General Information 233
    Ionizing Air Gun
    The ionizing air gun is an optional tool you may want to consider when cleaning iMac glass 
    panels. The ionizing gun performs electrostatic elimination and dust removal instantly with ion 
    balanced air.  Various sources can be found on Google. 
    						
    							iMac (20-inch Early 2008)  — Symptom Charts  234
    Symptom Charts 
    When to Use the Symptom Charts
    Before turning to the symptom charts, you should have completed the following steps on the 
    Apple General Troubleshooting Flowchart:
    Gather information
    1. 
    Verify the problem2.  
    Try quick fixes3. 
    You consult the symptom charts as part of the Research troubleshooting step (and sometimes as 
    part of the Try Quick Fixes step).
    How to Use the Symptom Charts
    The Symptom Charts included in this chapter will help you diagnose specific symptoms related 
    to the product. Diagnostic steps are listed on the charts in the order of most likely solution: try 
    the steps in the order presented. Verify whether or not the product continues to exhibit the 
    symptom. If the symptom persists, try the next step. 
    Important Note: If a step instructs you to replace a module, and replacing that module does not 
    resolve the symptom, reinstall the original module before you proceed to the next step.
    Diagnostics
    The following diagnostic tools are available for this product:
    Apple Hardware Test 
    • 
    Distributed to customers worldwide who purchase a new Apple computer -
    Apple Service Diagnostic:
    • 
    Sent to Apple Authorized Service Providers as part of the Macintosh Family Diagnostics  -subscription mailing
    See Knowledge Base document 11212 5, “Service Diagnostic Matrix”, to download the appropriate 
    disc images. The Service Diagnostics Matrix is a guide to service diagnostic software from Apple, 
    including the Apple Service Diagnostic, MacTest Pro, display service and adjustment utilities, and 
    Apple Hardware Test for MacBook, MacBook Pro, Mac mini, iMac, eMac, PowerBook, and Power 
    Mac products. 
    						
    							iMac (20-inch Early 2008)  — Symptom Charts  235
    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 is located.
    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)  — Symptom Charts  236
    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)  — Symptom Charts  237
    Power Issues
    System Intermittently Shuts Down or Restarts Unexpectedly
    Check the connection of the power cord on both ends. Verify that the power cord is securely 1. 
    plugged into a good AC outlet and that the cable is fully inserted into the back of the 
    computer. Did re-seating the power cord resolve the problem? 
     
    Yes: The power cord may have a loose fit or it wasn’t fully inserted into the receptacle on the 
    back of the iMac. Replace the AC power cord and test again. If the customer continues to 
    report shut down or restart issues resume with step 2 of this troubleshooting symptom.   
     
    No : Go on to the step 2.
    If the iMac has been previously serviced, verify that all cables and connectors are firmly 
    seated. Pay special attention to the DC power supply cable where it connects to the DC 
    power supply and the logic board (shown below). 
    Note: The latest version of the DC Power Supply/SATA/Inverter cable (922-8188) be identified 
    by the presence of a part number label on the end of the connector that plugs into the main 
    logic board. With earlier versions of the cable, the part number label is hidden by the chassis 
    and cannot be easily viewed when it is installed in an iMac.   
    						
    							iMac (20-inch Early 2008)  — Symptom Charts  238
    Does the computer continue to unexpectedly shut down or restart? 2. 
     
    Yes: Replace the DC, Power Supply/SATA/Inverter cable (922-8188) shown below. Note: The 
    latest version of the DC Power Supply/SATA/Inverter cable be identified by the presence of 
    a part number label on the end of the connector that plugs into the main logic board. With 
    earlier versions of the cable, the part number label is located on the cable, but the label is 
    hidden by the chassis, and cannot be easily viewed when it is installed in an iMac.    
     
    Carefully follow the take-apart instructions to ensure that the replacement cable is correctly 
    routed and the sensors and fans are properly connected. Test thoroughly. Run Apple 
    Hardware Test. Refer to the Apple Hardware Test Error Code Table if you incur an error.
     
    No : Return the computer to the customer. If the customer continues to report shut down or 
    restart issues during the next month resume with step 3 of the troubleshooting.
    Replace the power supply.
    3. 
    Replace the main logic board.4.   
    						
    							iMac (20-inch Early 2008) 
     — Symptom Charts 
     239
    No Power
    The computer will not turn on. The display remains black and there are no sounds from the fans 
    or drives.
    1. Verify the power outlet is good. Plug a different device into the socket to ensure there is power, 
    or plug the iMac into another outlet. Does the iMac power on now?
    Ye s: Resolved. Bad outlet.
    No : Go on to the next step.
    2. Check the power cord. Use a known good power cord. Does the iMac power on  now? Ye s: Your power cord has failed. Replace the AC power cord.
    No : Go on to the next step.
    3. Check the connection of the power cord on both ends. Verify that the power cord is securely 
    plugged into both the AC outlet and back of the computer. Does the iMac power on now? Ye s: You may have a loose fit to your power cord. Replace the AC power cord and test.
    No : Go on to the next step.
    4. Follow instructions in the General Information chapter to reset the SMC. Does the iMac power 
    on now? Ye s: Issue resolved.
    No : Go on to the next step.
    5.  Remove and reinstall the SO-DIMM memor y modules, located in the bottom of the computer. 
    Does the iMac power on now?
    Ye s: Issue resolved.
    No : Go on to the next step.
    6. Remove the memory access door and front bezel to gain access to the four diagnostic LEDs.  
    See “Diagnostic LEDs” in the General Information chapter for complete instructions on this 
    procedure.
    7. Plug the power cord into the iMac and the power cord into the AC outlet. Check to see if LED 
    #1 is On or Off. LED #1 is On: This indicates that the power supply is getting good power from the AC outlet. 
    Go on to the next step.
    LED #1 is Off: This indicates that the computer is not detecting AC power. If both the AC 
    outlet and the power cord are good, replace the AC/DC power supply. If the issue persists, 
    replace the AC line filter.
    8.  Press the power button. Check to see if LED # 2 comes On, comes on momentarily, or stays Off. 
    						
    							iMac (20-inch Early 2008)  — Symptom Charts  240
    LED # 2 is On: The Power Supply is functioning. Go on to the next step.
    LED # 2 comes on momentarily or stays Off: Replace the Power Supply.
    9. At this point in the Power On process, you should hear a boot chime and see that LED #1 and 
    #2 are On. Do you hear a boot chime? Ye s: The power systems of the computer are working correctly. See “Troubleshooting No 
    Video” in this chapter.
    No : The logic board is not passing the Power-On Self Test (POST ). Replace the SDRAM with 
    known-good memory and test. If the issue persists with known-good SDRAM, replace the 
    logic board.  
    Appears to be a “no power” situation, but the computer turns on, the display 
    remains black and the fans are running.
    Make sure all software updates have been applied to the computer. 1. 
    Check that all the temperature sensors are connected.2.  
    Run Apple Hardware Test to verify all sensors and cables are connected and functioning. 3. 
    Refer to the Apple Hardware Test Error Code Table  for additional information.
    Video
    No Video, No Boot Chime
    The computer will turn on, but there is no boot chime and no video on the display. The faint 
    sound of the fans, hard drive, and optical drive may  also be heard.
    1.  Make sure all software updates have been applied to the computer.
    2 Follow instructions in the “General Information” chapter to reset the SMC. Does the computer 
    display video after successfully resetting the SMC?
    Ye s: Problem solved.
    No : Continue to next step.
    3.  Verify that only supported SDRAM memory has been installed and that it has been installed 
    correctly. Unsupported and/or defective memory can prevent the computer from booting. It may 
    be necessary to install known good memory for testing purposes and replace any unsupported 
    or defective SO-DIMM’s identified during this process. Does the computer display video after 
    verifying and/or replacing the memory with known good memory? Ye s: Problem solved. Verify full system functionality before return the system to the customer.
    No : Replace the logic board. 
    						
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