Apple imac 17 inch User Manual

							
Logic Board Battery 
Important: Apple highly recommends removing the battery when handling the logic boa\
rd. Make 
sure to use proper ESD protection when handling modules. 
The battery on the logic board controls the stored system settings, such\
 as date and time. It is 
only necessary to test the battery when you can’t power on the comput\
er, or the date and time are 
reset every time the AC power is removed. 
The battery is also used to power the PMU chip (because the PMU chip ke\
eps time and must 
always be running) when the computer is unplugged from the wall (AC po\
wer). The PMU is 
very 
sensitive and touching any circuitry that is connected to the PMU can ca\
use it to crash. If the 
PMU crashes, the battery life goes from about five years to about two da\
ys if the PMU is not 
reset. Once the battery goes dead, the PMU will reset the time and date \
to 12:00 AM 1/1/04 
every time the AC power is removed. To fix this situation, replace the b\
attery and reset the PMU 
(refer to “Resetting the PMU on the Logic Board” mentioned earlie\
r in this chapter). 
If the computer has a “No Power” situation, check the battery befo\
re replacing modules. A 
drained battery may be indicative of a crashed Power Management Unit. 
Does the battery measure at least +3.5v? If not, replace the battery and\
 reset the PMU. If the 
battery does measure over +3.5v, reinstall the battery and reset the PMU\
 as above. 
Connect the power cord and power up the system again. 
Warning: Whenever the bottom housing is opened for service, you must  do two things: 
1. You must clean and reapply thermal paste to the thermal pipe surface.
2. You must tighten the four torx bolts on the base unit to a minimum of 1\
7 in.– lbs. Failure to follow 
either of these steps could cause the computer to overheat nd damage int\
ernal components. 
Refer to the next topic, “Thermal Paste Application” for detailed \
information. 
10 - iMac (Flat Panel) Troubleshooting
 General Information  
						

							
Thermal Paste Application 
The following instructions explain how to apply thermal paste to the thermal pipe in the iMac (Flat Panel) 
computer. Failure to follow these instructions could cause the computer to overhe\
at and damage internal 
components. 
Tools 
This procedure requires the following tools: 
• Plastic stylus or nylon probe tool (922-5065) to remove the old therma\
l paste 
• Thermal paste (922-4757), each tube contains 4-5 applications 
Procedure 
1.	Thoroughly clean the thermal film from the mating surfaces (circled below). Use a plastic stylus to scrape 
the surfaces clean.  Note:  Do not use an abrasive material or liquid cleaner. 
General Information	 iMac (Flat Panel) Troubleshooting -
11 
						

							
2 Squeeze a drop of thermal paste onto the middle of the thermal pipe surf\
ace as shown below. 
Note: In testing, the drop of thermal paste shown below completely covered the\
 entire 
thermal pipe surface. Place at  least this much paste on the thermal pipe. 
3.	Close the bottom housing. Securely fasten the four mounting torx screws very firmly (at least 17 in.– 
lbs. is necessary).  Important: If you don’t have access to a calibrated torque driver make certain that 
the screws are tightened firmly. You don’t need a torque driver; however, there is one available from 
Apple if you feel you need it. The torque driver part number is 076-0899. 
12 - iMac (Flat Panel) Troubleshooting	
 General Information  
						

							
Thermal Pad Replacement Instructions 
The following instructions explain how to replace the thermal pads in the iMac (Flat Panel) computer. These 
pads must be changed each time the main logic board is removed from the \
bottom housing.
 No tools 
are required for this procedure 
Procedure 
1.	Remove the old thermal pads (circled below) from the bottom housing.  Note:  If you don’t see all three 
thermal pads on the bottom housing, check the bottom side of the logic board. 
2.	Using the thermal pad kit, remove the clear protective backing from the new thermal pads. 
3.	Place the new thermal pads in the bottom housing.  Note: Avoid unnecessary contact with either side of 
the thermal pad as dirt and body oils reduce the thermal pad's conductivity. 
4.	Press down on the blue protective backing to make sure each thermal pad has even contact with the 
bottom housing. There should be no air pockets. 
5.	Remove the blue protective backing from the new thermal pads. 
6.	Replace the logic board.  Warning: Replace the thermal pads. Refer to “Thermal Pad Replacement 
Instructions” mentioned earlier in this chapter. 
General Information	 iMac (Flat Panel) Troubleshooting -
13 
						

							
Symptom Charts

How to Use the Symptom Charts 
The Symptom Charts included in this chapter will help you diagnose specific symptoms related to the 
product. Because cures are listed on the charts in the order of most likely solution, try the cures in the 
order presented. Verify whether or not the product continues to exhibit the symptom. If the symptom 
persists, try the next cure. 
Note:  If you have replaced a module, reinstall the original module before you proceed to the next cure. 
Apple Hardware Test 
Apple Hardware Test is a diagnostic tool for detecting problems with Apple internal hardware components 
such as logic board, memory, modem, video RAM, and Apple AirPort Card. The test does not check 
externally connected hardware components such as USB or FireWire devices; it also does not check non-
Apple devices such as third-party PCI cards. 
Note:  The most recent Apple Hardware Test software can be downloaded from the CD Images page on 
AppleCare Service Source; go to the Service Source home page and select ‘Disc Images’ from the quick-
click table. 
Error Codes 
If Apple Hardware Test detects a problem with a computer, it displays an error code, which is defined in the 
product's Error Code List. Consult the list for appropriate repair procedures associated with the code. 
All Error Code Lists are included in the Service Diagnostics Matrix, Knowledge Base article 112125. You 
can also access this matrix by clicking the Service Diagnostics rollover link under any of the product areas 
on the Service Source home page. 
14 - iMac (Flat Panel) Troubleshooting
 Symptom Charts  
						

							
No Power 
The computer will not power on. 
1.	Verify the power outlet is good. Plug a different device into the socket to ensure there is power, or plug 
computer into another outlet. 
2.	Check the power cord. Use a known good power cord. 
3.	Check connection of the power cord on both ends. Verify that the plug is securely plugged into both the 
A/C outlet and back of the computer. 
4.	Remove keyboard, mouse, and other peripherals such as speakers. 
5.	Disconnect the power cord, place the computer in the service stand, and remove the user access plate. 
6.	Reset PMU. Refer to “Resetting the PMU on the Logic Board” mentioned earlier in this chapter or Kbase 
article 95165. 
7.	Verify the battery is good before replacing modules. A drained battery may be indicative of a crashed 
Power Management Unit. Does the battery measure at least +3.5v? If not, replace the battery and reset 
the PMU. If the battery does measure over +3.5v, reinstall the battery and reset the PMU. 
8.	Connect the diagnostic cables (part 076-0897) between the upper housing components and the logic 
board. Refer to “Service Cables” mentioned earlier in this chapter.  Important: Diagnostic service cables 
allow the unit to run while the bottom housing is open (as shown above). However, the computer cannot 
run for more than five minutes with the bottom housing open. If it is open longer, the CPU may overheat 
and become damaged. 
9.	Check the connection of the video cable on the LCD flat panel, and try to power on the unit again. 
10. Check the AC line filter. To measure power at the AC line filter cable, disconnect the AC line filter cable 
from the power supply cable. Switch your multimeter to read AC voltage. Touch the black probe to the pin 
of the brown wire, and touch the red probe to the pin of the blue wire (see graphic below). Do you 
measure 120v (line voltage)? If yes, go on to step 11. If no, replace the AC Line Filter. 
No Power Symptom Charts	 iMac (Flat Panel) Troubleshooting -
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11. Check power supply output. Disconnect the diagnostic power cable from the power supply connector, 
and measure power at the power supply connector by touching the black probe to the ground pin, and 
using the red probe to measure power at the pins indicated in thegraphic below. Did you measure +12v 
at each point? If yes, continue with the next step. If no, replace the power supply. 
12. Check the main logic board voltages. Measure for +12v DC at capacitors C187 and C197 (identified in 
graphic below). Ground the black probe to the logic board screw next to the battery, and touch the red 
probe to the positive node at capacitor C187, and then at capacitor C197. Do you measure +12v? If 
yes, go on to the next step. If no, replace the logic board. 
13. Replace power supply. 
14. Replace the logic board. 
15. Replace the inverter board. 
16. Replace neck assembly. 
16 - iMac (Flat Panel) Troubleshooting 
No Power Symptom Charts  
						

							
No Video 
The screen is dark, fan and hard drive are spinning. 
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. With the unit powered on, check if a red LED (shown below) is visible in 
the access door. If the red LED is on, power is on. If you don’t see the red LED glowing red, follow the 
steps under the “No Power” symptom. 
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 using an Apple VGA Display 
Adapter, part # M8639G/A. Make sure your monitor supports the following resolutions and refresh rates: 
• 640 x 480 @ 60 Hz 
• 800 x 600 @ 75 Hz 
• 1024 x 768 @ 75 Hz 
If the unit has external video, the video chip on the logic board is put\
ting out a good signal. Go on to 
step 6. If there is no external video, but the unit appears to be operat\
ing normally otherwise, replace the 
logic board. 
6.	Open the bottom housing and verify that all the cables are securely attached to the logic board. Pay 
special attention to the video cable connector (located near the modem). Reconnect cables and try 
again. 
7.	Recheck all the connections to the panel before replacing the panel. Pay special attention to the flat 
video cable connection (under copper tape) going into the LCD panel. 
No Video Symptom Charts	 iMac (Flat Panel) Troubleshooting -
17  
						

							
8. Replace the inverter board. 
9. Replace the LCD display. 
10. Replace the neck assembly 
11. Replace the logic board. 
12. Replace the power supply board. 
18 -iMac (Flat Panel) Troubleshooting 
No Video Symptom Charts  
						

							
Display 
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: 
LCD Size 
(inches) Acceptable Number of Subpixel 
Anomalies Replace the Display 
Bright Dark Combination Bright Dark Combination 
12.1  to  15.2 up to 3 up to 5 up to 7 4 or more 6 or more 8 or more 
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. 
Display Symptom Charts	 iMac (Flat Panel) Troubleshooting -
19