Apple imac usb 2 0 User Manual

							
16 - iMac (USB 2.0) Troubleshooting
No Video Symptom Charts
No Video 
Screen is dark, fan is running and the hard drive is spinning. You may hear the startup 
chime as well.
1. Reset parameter RAM. Press Command-Option-P-R during startup before “Welcome to Macintosh” 
appears.
2. The system software could be damaged. Start up from the system CD that came with the computer.
3. Remove the user access panel on the bottom of the computer. With the unit powered on, check if a red  LED is visible in the access door. If the red LED is on, power is on. If you don’t see the LED glowing 
red, follow the steps under the symptom “No Power”. 
4. Disconnect the A/C power cord. Place the unit in the service stand and remove the user access plate.  Press the PMU reset button on the logic board. Refer to “Resetting the PMU on the Logic Board” 
mentioned earlier in this chapter.
5. Check for external video. Connect an external monitor to the mini-VGA port. If you don’t have external  video, replace the main logic board. If you do have external video, go on to the next step.
6. Open the bottom housing and verify that all the cables are securely attached. Pay special attention to  the video cable (located near the modem). If the cables are securely attached, go on to the next step. 
Warning:   Whenever the bottom housing is opened for service, you must  do two things:
• You must clean the original thermal film from the surfaces joining the t\
hermal interface layer and  reapply thermal paste to the thermal pipe.
• The bottom housing has four torx screws that must be tightened to at lea\
st 17 in.-lbs. If you do not  have a torque driver, you will have to make sure these screws are tighte\
ned by hand FIRMLY, BUT 
NOT FORCIBLY. Or, purchase the service tool (076-0899) in order to ens\
ure the thermal pipe is 
firmly mated with the top base. If the bottom housing is not securely at\
tached to the base in this 
fashion, the CPU may overheat and become damaged.
7. Check the connection of the video cable to the LCD flat panel display (under black tape). 
8. Replace the inverter board.
9. Replace the LCD display.  Important: If you are replacing the display, be sure to install the new display 
shield and EMI gaskets that come with the new LCD panel. Installation instructions are included with 
the new display panel. Additional display shields/gasket kits are also available separately as a kit, part 
#076-0958.
10. Replace the neck assembly
11. Replace the logic board. 
12. Replace the power supply board. 
						

							
iMac (USB 2.0) Troubleshooting - 17
No LED Symptom Charts
No LED
LED on the 17-inch display bezel does not light up
Note:  The LED does not light up when the power is on; however, the LED should pulse when the computer is 
in Sleep mode. 
1. Put the computer into Sleep mode. Does the LED pulse now? If yes, there is nothing wrong with the LED.  If no, replace the display bezel (922-5297). The LED is attached to the display bezel and cannot be 
ordered separately.
LED on the 15-inch display bezel does not light up
1. Put the computer into Sleep mode. Allow the machine to remain in sleep mode for one minute and then wake the computer to ensure the computer is waking from sleep mode. Does the LED pulse now? If yes, 
there is nothing wrong with the LED. If no, replace the LED (922-4702).  Note: The LED on the 15-inch 
panel can be ordered separately. 
						

							
18 - iMac (USB 2.0) Troubleshooting
Display Tilt Symptom Charts
Display Tilt
Screen tilts to the left or the right even after a manual adjustment.
Note:  It is normal for the screen on an iMac (Flat Panel) to have a small amount of horizontal play. 
However, the screen should be able to be adjusted so that it will stay in a level horizontal position.
1. Remove the flat panel.
2. For the 15-inch: Remove the three screws and lift the cable retainer off the panel shield.
3. For the 17-inch: Remove the four screws and lift the cable retainer off the back panel. 
						

							
iMac (USB 2.0) Troubleshooting - 19
Display Tilt Symptom Charts 4. For either size display, loosen the screws under the metal cable retainer and tilt the screen the opposite 
direction of the tilt.  Note:  The picture below shows the four screws on the 15-inch model; the 17-inch 
model looks very similiar. 
5. While holding the display bezel in the level position, tighten the screws.
6. Replace the panel and check that the display is now horizontally level.  Important: If you are replacing 
the 17-inch display, be sure to install the new display shield and any EMI gaskets that may come with the 
new LCD panel. 
						

							
20 - iMac (USB 2.0) Troubleshooting
Display Tilt Symptom Charts
When displaying a single color over the screen area, the LCD panel shows one or more 
pixels that are not properly lit
Active-matrix LCD technology uses rows and columns of addressable locations (pixels) that render text 
and images on screen. Each pixel location has three separate subpixels (red, green, and blue) that allow 
the image to be rendered in full color. Each subpixel has a corresponding transistor responsible for turning 
the subpixel on or off.
There are typically millions of these subpixels on an LCD display. For example, the LCD panel used in the 
Apple Cinema HD display is made up of 2.3 million pixels and 6.9 million red, green, and blue subpixels. 
Occasionally, a transistor does not work perfectly, which may result in the affected subpixel being turned on 
(bright) or turned off (dark). With the millions of subpixels on a display, it is quite possible to have a low 
number of faulty transistors on an LCD. Therefore, a certain number of subpixel anomalies is considered 
acceptable. Rejecting all but perfect LCD panels would significantly increase the retail price for products 
using LCD displays. These factors apply to all manufacturers using LCD technology—not just Apple 
products.
To determine whether or not the display has an acceptable number of pixel anomalies, follow the steps 
below:
1. Set the display image to one of the following colors: all-white display, all-red display, all-green display, 
or all-blue display.
2. Using a jeweler’s loupe, pocket microscope, or other magnifying device, identify and count each  subpixel anomaly:
• Bright subpixel anomaly = subpixel that is always on
• Dark subpixel anomaly = subpixel that is always off
3. Important:  Check the number of subpixel anomalies with the following chart:
4. If the number of subpixel anomalies exceeds the acceptable number listed in the chart, replace the  LCD panel.
5. If the number of subpixel anomalies is acceptable, explain to the customer that the pixel anomalies are  within specifications, and no repair is necessary. 
Important:   Do not release the specifications to customers. Instead, inform them t\
hat a certain 
number of subpixel anomalies is considered acceptable, and these factors apply to all manufacturers 
using LCD technology—not just Apple products.
LCD Size 
(inches)
Acceptable Number of Subpixel 
Anomalies Replace the Display
Bright
Dark Combination BrightDark  Combination
17 to 20 up to 4 up to 6 up to 8 5 or more 7 or more 9 or more 
						

							
iMac (USB 2.0) Troubleshooting - 21
Hard Drive Symptom Charts
Hard Drive 
Hard Drive won’t mount to the desktop
1. Disconnect any connected peripherals.
2. Boot from the system CD that came with the computer and see if the hard \
drive mounts on the desktop.
3. Launch Drive Setup and update the hard drive driver.
4. If no hard drive is found in Drive Setup, verify the hard drive cable connections.
5. Replace the hard drive cable.
6. Replace the hard drive.
7. Replace the logic board.
Flashing question mark appears on the screen
1. Boot from the system CD that came with the computer and see if the hard \
drive mounts on the desktop.
2. Launch Drive Setup and update the hard drive driver.
3. If no hard drive is found in Drive Setup, verify the hard drive cable connections.
4. Replace the hard drive cable.
5. Reinstall the software drivers for the hard drive.
6. Reinstall system software. Backup the data first.
7. Reinitiation the hard drive.
8. Replace the hard drive.
9. Replace the logic board.
System hangs during normal startup process
1. Boot from the system CD that came with the computer and see if the hard \
drive mounts on the desktop.
2. Using Drive Setup, reinstall the system software drivers for the hard drive.
3. Using Drive Setup, reinitiation the hard drive.
4. Check all cable connections to and from the hard drive.
5. Replace the hard drive cable.
6. Replace the hard drive.
7. Replace the logic board. 
						

							
22 - iMac (USB 2.0) Troubleshooting
Optical Drive Symptom Charts
Optical Drive 
Optical drive won’t mount to the desktop
1. Try cleaning the disc. If it is dirty or scratched, it may not mount.
2. Try a different disc.
3. Boot from Apple Hardware Test (hold down the “C” key at startup) or boot from the system install CD 
(use Startup Manager, hold down the Option key at startup).
4. Perform a clean install with the CD that came with the computer.
5. Replace the optical drive cable.
6. Replace the optical drive.
7. Replace the logic board.
Can’t boot from the optical drive
1. Try cleaning the disc. If it is dirty or scratched, it may not mount.
2. Try a different disc.
3. Boot from Apple Hardware Test (hold down the “C” key at startup) or boot from the system install CD  (use Startup Manager, hold down the Option key at startup).
4. Perform a clean install with the CD that came with the computer.
5. Replace the optical drive cable.
6. Replace the optical drive.
7. Replace the logic board.
Optical disc constantly ejects
1. Disconnect all peripheral devices, especially the mouse in cases where the disc is constantly ejecting.
2. Try cleaning the disc. If it is dirty or scratched, it may not mount.
3. Try a different disc.
4. Boot from Apple Hardware Test (hold down the “C” key at startup) or boot from the system install CD  (use Startup Manager, hold down the Option key at startup).
5. Perform a clean install with the CD that came with the computer.
6. Replace the optical drive cable.
7. Replace the optical drive.
8. Replace the logic board. 
						

							
iMac (USB 2.0) Troubleshooting - 23
Sound Out Symptom Charts
Sound Out  
No sound from either internal or external speakers
1. Verify volume setting is correct in system preferences.
2. Replace the external speakers or headphone in question with a known-good device.
3. Reset parameter RAM. Press Command-Option-P-R during startup before “Welcome to Macintosh” 
appears.
4. Verify internal speaker cable is connected.
5. Replace the internal speaker.
6. Replace the logic board. 
						

							
24 - iMac (USB 2.0) Troubleshooting
Sound In Symptom Charts
Sound In 
No sound is recorded
1. Check System Preferences > Sound > Input and make sure that Internal microphone is selected, and 
that the input volume is at a reasonable level to pick up sound. Use the Input level indicator to judge if 
the microphone is picking up sound.
2.  Check the microphone cable connection.
3. Replace the internal microphone. The internal microphone cable assembly is part of the of 20 and 17  Display bezel, and cannot be ordered separately. For the 15 model, you can order the microphone 
cable assembly separately as part 922-4703. 
4. Replace the neck assembly. 
						

							
iMac (USB 2.0) Troubleshooting - 25
Error Beep(s) Symptom Charts
Error Beep(s)
Computer beeps at startup.
1. RAM expansion DIMMs for the iMac must be DDR 333 PC2700 compliant SDRAM devices. If the user 
installs a DIMM that uses EDO or SGRAM devices, the computer will beep several times when the user 
attempts to restart the computer.
2. Refer to “Power-On Self Test” mentioned earlier in this chapter.