Apple imac usb 2 0 User Manual

							
132 - iMac (USB 2.0)  Take Apart
 Neck Assembly, 20" and 17" Displays
• Remove the power supply insulators.
• Remove the fan.
• Remove the fan bracket.
• Remove the neck spoke retainer cap.
• Remove the blind mate connector screws.
• Remove the Faraday cage.
• Remove the outer plastic housing.
• Remove the flat panel display.
• Remove the back cover 
Procedure
1. To remove the neck assembly, follow all the preliminary steps mentioned above. When 
you are finished, you will be left with the iMac (USB 2.0) neck assembly. The neck 
assemblies for the 20-inch and the 17-inch iMac (USB 2.0) are shown below.
2. The 20-inch neck, 661-2990, can be identified by the part number on the TMDS cable  (circled). The part number should read 620-2580.
3. The 17-inch neck, 661-2825, can be identified by the part number on the TMDS cable  (circled). The part number should read 620-2305 
						

							
 iMac (USB 2.0)  Take Apart - 133
 Neck Assembly, 15" Display
Neck Assembly, 15 Display
Tools
This procedure requires the following tools:
• Torx-10 screwdriver
Part Location
Preliminary Steps
Before you begin, do the following:
• Position the computer in the service stand.
• Remove the user access plate.
• Remove the bottom housing.
• Remove the drive carrier assembly.
• Remove the power supply.
• Remove the power supply insulators.
• Remove the fan. 
						

							
134 - iMac (USB 2.0)  Take Apart
 Neck Assembly, 15" Display
• Remove the plastic cable retainer (under the fan).
• Remove the cap spoke holder.
• Remove the blind mate connector screws.
• Remove the Faraday cage.
• Remove the flat panel display.
• Remove the panel shield.
• Remove the back cover 
Procedure
The neck assembly (661-2969) for the 15-inch iMac (USB 2.0) computer is shown below. It 
can be identified by the part number on the TMDS cable (circled). The part number should 
read 620-2384. 
						

							
 iMac (USB 2.0)  Take Apart - 135
 Neck Assembly, 15" Display 
						

							
© 2003 Apple Computer, Inc. All rights reserved.
 Service Source
Troubleshooting
iMac (USB 2.0) 
						

							
iMac (USB 2.0) Troubleshooting - 1
 General Information
General Information
Overview:
How do you identify the different models?
1. Identify the different models by their serial number. Search for the serial number in GSX (Global Service 
Exchange) under the “Parts Lookup” or search in the Service Parts Database.
2. Identify the processor speed. If the system is up and running, select “About this Mac” under the Apple  icon in the Finder. Or, select the “More Info” button on the “About this Mac” window. Apple System 
Profiler opens and displays the machine speed under “Hardware Overview.” The 15-inch iMac has a 
1GHz PowerPC G4 processor and the 17-inch and 20-inch iMac have a 1.25GHz PowerPC G4 
processor. 
3. Identify the various neck assemblies by referring to the topic “Neck Extension Identification” in Take  Apart, or by referring to the Knowledge Base article 86525, “iMac: Flat Panel Neck Assembly 
Differences”. 
4. These computer models uses double-data rate (DDR) memory; PC2700 DDR333. Memory from  previous iMac models is not compatible with this computer. Do not use older SDRAM DIMMs or SO-
DIMMs even if they fit into the slot. Make sure to use PC2700 DDR333 low profile SO-DIMMs in the user-
installable slot. The iMac memory pinouts are 184-pin internal, and 200-pin on the user-installable slot.
Important Things to Remember:
Service items that still apply to all flat-panel iMac computers:
1. Diagnostic test points are on to the logic board. They are accessed through the user access door. Use the test points to check the following:
• Battery
•5V
• 12VSLP 
• 12V
For more information, refer to the “Logic Board Battery” and “N\
o Power” topics later in this 
chapter.
2.Important:  The CPU uses a thermal pipe to transfer heat away. This pipe makes a thermal connection to 
the top metal chassis (Faraday cage) at  two locations. These connecting points must be cleaned and 
have new thermal paste applied each time the bottom housing is removed. If the mating surfaces are not 
cleaned and thermal paste is not used, the CPU may overheat and become damaged. There is no 
exception to this.  Note:  Most service procedures require that the bottom housing is removed. 
Refer to “Thermal Paste Application” mentioned later in this chapt\
er or in the Take Apart 
chapter. 
						

							
2 - iMac (USB 2.0) Troubleshooting
 General Information
3. Whenever the17-inch LCD display (661-2715) is replaced, a display shield/gasket kit (076-0958) must 
be installed on the new panel. Instructions for installing the shield/gasket kit are included with the new 
LCD panel.
4. The LED and microphone are part of the 17-inch display bezel (922-5297); they cannot be ordered  separately.
5. The LED functions differently on the iMac (17-inch Flat Panel). The LED  does not light up when the 
power is on; however, the LED should pulse when the computer is in Sleep mode. 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 number 076-0958.
6. Important:   Whenever the logic board is separated from the bottom housing, you must install new 
thermal pads to two surfaces on the bottom housing. The thermal pads help cool components on the 
logic board. Failure to apply these pads whenever the logic board is separated from the bottom 
housing could cause these parts to overheat. Short term separation, where the thermal pads are not 
handled excessively 
(an exception would be if you are simply testing the logic board and only detach it 
for a few minutes), does not require replacement. Refer to “Thermal Pad Installation” in this chapter for 
detailed information.
Refer to the Take Apart chapter, “Thermal Pad Installation.”
7.  Whenever the bottom housing is opened for service, you must  do two things:
1.You must clean the original thermal film from the surfaces joining the\
 thermal interface layer and 
reapply thermal paste to the thermal pipe.
2. You must tighten the four torx screws on the bottom housing to a mini\
mum of 17 in.-lbs. If you do 
not have a torque driver, you will have to make sure these screws are ti\
ghtened by hand FIRMLY, 
BUT NOT FORCIBLY. Or, purchase the service tool (076-0899) in order to\
 ensure 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. Failure to follow eith\
er of these steps could 
cause the computer to overheat and damage internal components. 
Refer to the topic, “Thermal Paste Application” for detailed infor\
mation.
8. A service stand, 076-0898, is available from Apple Service to hold the unit while you service the  computer. 
						

							
iMac (USB 2.0) Troubleshooting - 3
 General Information
Logic Board, Top  
						

							
4 - iMac (USB 2.0) Troubleshooting
 General Information
Logic Board, Bottom 
						

							
iMac (USB 2.0) Troubleshooting - 5
 General Information
I/O Ports
The PMU Chip
The PMU (Power Management Unit) is a microcontroller chip that control\
s all power functions for 
the computer. The PMU (location shown below) is a computer within a co\
mputer. It has memory, 
software, firmware, I/O, two crystals, and a CPU. Its function is to: 
• Tell the computer to turn on, turn off, sleep, wake, idle, etc.
• Manage system resets from various commands.
• Maintain parameter RAM (PRAM).
• Manage the real-time clock.
Important: The PMU is very sensitive and touching the circuitry on the logic board can cause the 
PMU to crash. If the PMU crashes, the battery life goes from about five \
years to about two days if 
the PMU is not reset. Refer to the next topic, “Resetting the PMU on \
the Logic Board” for the 
procedure. 
Many system problems can be resolved by resetting the PMU chip. 
                                                       Location of the P\
MU Button