Apple imac 20 inch early 2008 User Manual

							iMac (20-inch Early 2008) 
  —  Sym pt om   Char t s    2 41
No Video, Boot Chime Heard
The computer will turn on, the boot chime is heard and fan or drive activity can be heard, but the 
display has no picture or color.  
1. Make sure all software updates have been applied to the computer.
2. Check if the computer is sleeping. Press the space bar to wake the computer from sleep mode. 
Did the computer wake from sleep?
Yes: Put the computer to sleep from the Apple menu and wake the computer again to test. 
Check Energy Saver setting to see when the computer has been designated to sleep.
No: Continue to next step.
3.. Reset your computer’s PRAM (Parameter RAM): Shut down the computer.
 -Locate the following keys on the keyboard: Command, Option, P, and R. 
 -Turn on the computer.
 -Press and hold the Command-Option-P-R keys simultaneously. You must press this key 
 -combination before the gray screen appears.
Hold the keys down until the computer restarts and you hear the startup sound for the 
 -second time.
Release the keys.
 -
4. Does the computer display video after successfully resetting the computer’s PRAM? Ye s: Restart the computer from the Apple menu and make sure the computer is working 
correctly before returning the computer to the customer.
No : Continue to next step.
5. Make sure the machine is powered off, and remove the access door and front bezel to access 
the diagnostic LEDs . Plug in and start up the computer to observe the diagnostic LEDs. At this 
point in the Power On process, you should hear a boot chime, and LED #1 and #2 are On. Is LED 
#3 On or Off?
LED # 3 is On: The video card and logic board are communicating properly. Go to the next 
step.
LED # 3 is Off: The video card and logic board are not communicating. Replace the video 
card. If the issue persists, replace the main logic board.
6. LED #4 should be On when the video card and LCD display have communicated properly to 
produce a video image. Is LED #4 On or Off? LED # 4 is On: The video card and LCD display have communicated to LCD video. In this case, 
there is a problem with the backlights in the panel or the inverter. First, make sure the four 
inverter cables are fully inserted into the panel connectors and check that the four wires 
have not been pinched.  Next, with the computer powered on, turn the display at an angle to 
you and look closely at the display. It may be necessary to dim the room lights. Is the display  
						

							iMac (20-inch Early 2008)  — Symptom Charts  242
completely black, or can you see a dim light or purple glow to the display? 
Completely black: Replace the inverter.
Dim light or purple glow: The inverter and panel backlights are functioning. Replace the 
LCD display panel.
LED # 4 is Off: The video card and logic board are unable to communicate to generate video. 
Replace the video card.
Display is tinted another color
The iMac computer has a tinted glass panel covering the display, giving it a new look from 1. 
previous models. Make sure this not what the customer is referring to.
Reset the parameter RAM. Press the Command-Option-P-R keys. When you keep all the keys 
1. 
held down, you will hear the startup chime over and over again (about every ten seconds) 
until you let go. After you hear the second chime, you can let go of the keys.  
Does the computer display video after successfully resetting the computer’s PRAM?  
Yes: Problem resolved. Restart the computer from the Apple menu and make sure the 
computer display is no longer tinted another color.  
No: Continue to the next step.
Connect an external monitor to the mini-
2.  DVI port. Does the external display exhibit the same 
color tinting?  
Yes: Replace the video card . 
No: Check the LVDS cable connections . If connected properly and the same color tinting 
persists, replace the LVDS cable. Does color tinting persist after changing the LVDS cable? 
 Yes: Replace the LCD display panel.  
 No: Problem solved. Restart the computer from the Apple menu and make sure the 
computer display is no longer tinted another color.
System Shuts Down
Unexpected Shutdown or Freezes
If the computer freezes or you experience unexpected shutdowns while using your 1.  
applications, make sure all software updates have been applied to the computer. If this 
doesn’t solve the issue, go on to the next step.
Follow the steps under “
2.  System Intermittently Shuts Down or Restarts Unexpectedly.”
Display
Black and white splotches on the LCD panel after it runs for awhile
Check the hard drive. The hard drive should be mounted with the circuit board facing up or out 
towards the LCD as shown in the hard drive chapter . It’s possible to mount the hard drive upside 
down (hard drive top cover facing LCD) which generates a corrupted image (black and white 
splotches) on the LCD panel after it runs a while.  
						

							iMac (20-inch Early 2008)  — Symptom Charts  243
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:
Set the display image to one of the following colors: all-white display, all-red display, all-green 
1. 
display, or all-blue display.
Using a jeweler’s loupe, pocket microscope, or other magnifying device, identify and count 
2.  
each subpixel anomaly:  
• Bright subpixel anomaly = subpixel that is always on 
• Dark subpixel anomaly = subpixel that is always off 
Important: 
3. Check the number of subpixel anomalies with the following chart:  
 
LCD Size 
(inches) Acceptable Number of Subpixel 
Anomalies Replace the Display
Bright Dark Both Bright Dark Both 
24 up to 8 up to 10up to 159 or more 11 or more16 or more
If the number of subpixel anomalies exceeds the acceptable number listed in the chart, 
4.  
replace the LCD panel.
If the number of subpixel anomalies is acceptable, explain to the customer that the pixel 
5. 
anomalies are within specifications, and no repair is necessary. 
Important:  Do not release the specifications to customers. Instead, inform them that a 
certain number of subpixel anomalies is considered acceptable, and these factors apply to all 
manufacturers using LCD technology—not just Apple products. 
						

							iMac (20-inch Early 2008)  — Symptom Charts  244
Hard Drive
Flashing question mark, or an alternating question mark and Mac OS (face or a 
folder)
Note: When troubleshooting hard drive problems it is a good idea, if possible, to back up any 
important data. Some troubleshooting steps may require erasing the contents of the hard drive.
Boot from the system CD that came with the computer, and open Disk Utility. Does the hard 
1. 
drive show in Disk Utility? 
Yes: Run Repair Disk and Repair Permissions to correct any directory and permissions issues. 
Go on to Step 2.  
No: Go to Step 3.
Did Disk Utility successfully repair directory or permissions? 
2.  
Yes: Restart the computer to the hard drive. Go on to Step 3.  
No: Go to Step 3.
Did the computer successfully start to the internal Hard Drive? 
3. 
Yes: Run Apple Hardware Test for this machine and return to the customer if it passes.  
No: Boot the machine to Apple Hardware Test or to the Apple Service Diagnostic.
Did the machine successfully boot to the Diagnostic? 
4.  
Yes: Run the test suites.   
No:  Make sure you’re using the correct version of the Diagnostic, and that the disc is able to 
boot another machine that it supports. If so, then try booting from an external optical drive. 
If this is successful, you should replace the optical drive and retest the machine booting to 
the diagnostic disc.   
Did the tests pass? 5. 
Yes: Reinstall the System Software that came with the computer and test.   
No: 
Replace the component (s) indicated by the test results.   
						

							iMac (20-inch Early 2008)  — Symptom Charts  245
Hard Drive Information
Note: The following information is for Intel-based and PPC Macintosh drive compatibility
Drives to be used in booting Intel-based Macintosh hardware should be formatted and 
• 
partitioned with an Intel-based Macintosh disk utility running on Intel-based Macintosh 
hardware. That should ensure you get the correct default partition map and structure for 
reliable booting.
Intel-based Macintosh CPUs in Target Disc Mode will only mount on PPC machines running 
• 
Mac OS X 10.4.10 or later, and may show one contiguous partition rather than separate 
partitions on the host machine.
Always make sure to use the OS that came with the machine if you need to reinstall software 
• 
(ask the customer for the discs if necessary), and the diagnostics specifically designated for 
that hardware.
System hangs during normal startup process
1. Make sure all software updates have been applied to the computer.
2. Boot from the system CD that came with the computer. Use Disk Utility to verify the hard drive.
3. Using Disk Utility, reformat the hard drive.
4. Check all cable connections to and from the hard drive.
5. Replace the hard drive data cable.
6. Replace the hard drive.
7. Replace the logic board. 
						

							iMac (20-inch Early 2008)  — Symptom Charts  246
Optical Drive 
Optical drive won’t eject media
Carefully remove the EMI tape on the top of the optical drive.  1. 
Caution: The optical mechanism is VERY delicate and should be handled with care. Handle 
the drive by the sides and the back edge. Avoid touching the front of the drive and putting 
pressure on the top and bottom cover. 
Verify that two or three black clips (as shown below) are positioned on top of the optical 2.  
drive mechanism. Note:  The number of clips on the bezel depends on which mechanism 
is used, there are multiple optical vendors. Some bezels have two clips, others have 
three. Are the clips visible? 
Ye s : Clips on top of the bezel (as shown below) indicates a correctly installed optical carrier. 
Inspect the carrier opening and test it again.  
No : Inspect the bezel for clips stuck under the bezel. If they are stuck, go to the next step.   
						

							iMac (20-inch Early 2008) 
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Remove the optical drive. Look at the optical drive from the front. Inspect the carrier 3. 
opening, make sure it’s even all the way across. If a clip is caught under the optical 
mechanism, the optical drive mechanism will be bowed or warped. Is the mechanism bowed 
or warped?  
Yes: Remove the four T8 shoulder screws on the carrier. Reseat the carrier so the black clips 
are visible on top of the optical mechanism. Test the optical drive. If the optical drive won’t 
eject media, replace the optical drive and test again.  
No : Reset the optical drive, run diagnostics, and return the computer to the customer.
Replace the four T8 carrier screws.4. 
Place the optical drive into the computer.5. 
Replace the EMI tape on top of the drive.6. 
Test the optical drive by inserting and ejecting the media.7. 
If the issue continues, replace the optical drive.8.  
Disc will not eject
Verify disc is not in use by quitting any applications that may be using the disc.1. 
Verify drive slot is not blocked, bent, compressed or damaged.2.  
Press and hold Media Eject key at top right corner of keyboard. If that does not work, hold 3. 
down Function (fn) key then Media Eject key in sequence, then together simultaneously. 
Drag disc icon to trash, or select it and press Command-E.
4. 
If none of these options eject the disc, you may have to disassemble the drive to recover the 5. 
disc. See Knowledge Base article 8638 2 - “Macintosh: How to Remove a Stuck Disc From a 
Slot-Loading Drive.”
Reseat the optical drive mechanism in the rear housing. 
6.  
Disconnect all peripheral devices, especially the mouse in cases where the disc is constantly 7. 
ejecting. Retest. If the issue is resolved, reconnect peripherals one-at-a-time until faulty 
peripheral is identified
Replace the optical drive flex cable.
8.   
						

							iMac (20-inch Early 2008)  — Symptom Charts  248
Replace the optical drive.
9. 
Replace the logic board10.
  
						

							iMac (20-inch Early 2008) 
 — Symptom Charts 
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CDs or DVDs don’t show up on the Desktop
Select Preferences from the Finder menu and make sure the option to show CDs, DVDs and 1.  
iPods is checked: in the General window as shown below.   
						

							iMac (20-inch Early 2008)  — Symptom Charts  250
Select System Preferences from the Apple menu and open the CDs & DVDs preferences 
2.
 
window. Make sure that audio CDs are set to launch iTunes and movie DVDs set to launch 
DVD Player when those media are inserted, as shown below.  
Check that the drive can read discs normally. Insert an audio CD and check whether it shows 3. 
up on your desktop or launches iTunes.  
Does the audio CD mount on the desktop or in iTunes? 
Yes: The drive seems to read CD discs okay. Go on to Step 4. 
No: Make sure the disc is readable by other computers. Try other CD discs. If none mount or 
no audio CDs launch iTunes, replace the optical drive.”
Eject the audio CD and insert the iMac Software Install and Restore DVDs that came with the 
4.  
customer’s computer, or insert a DVD movie.  
Does this disc show up on the desktop, or does the movie launch DVD Player?  
Yes: The computer is reading CD and DVD media. This may be related to a specific disc or 
discs the customer is using and you should examine those discs.  
No: The optical disc is reading CD media, but not DVD media. Try other DVD discs. If none 
mount or movie DVDs do not launch DVD Player, replace the optical drive flex cable.
If after replacing the optical drive flex cable the drive still won’t mount any optical media, 
5. 
replace the optical drive. If the issue persists, then replace the logic board.