Apple imac 17 inch User Manual

Service Source

Troubleshooting 
iMac (Flat Panel) 
© 2002 Apple Computer, Inc. All rights reserved.  

General Information

What’s New and Different (2003): 
1.	The iMac (Flat Panel) with serial number xx305xxxxxx or later (released in February 2003) will start up 
only in Mac OS X. This model can run Classic, but it will not start up in Mac OS 9. You can also identify 
iMac (Flat Panel) units that only boot to Mac OS X by the Boot ROM information in the Apple System 
Profiler. Under System Profile > Hardware Overview > Boot ROM info should read 4.5.0f4 or later for 
iMac (Flat Panel) machines which only...

6.	The display is a TFT LCD panel with a maximum resolution of 1024 x 768. The display is connected to 
the unit via a tilt and swivel neck extension. 
7.	Optical drive is now tray-loading, and is either a CD-RW, a DVD-ROM/CD-RW (Combo drive), or a 
DVD-R/CD-RW (Superdrive). 
8.	The computer contains a variable-speed fan. The fan speed increases as the unit needs more cooling. 
9.	The unit does not have NMI or Reset buttons. These functions have been taken over by the power 
button. 
10. The sound-out...

Block Diagram 
The following illustration provides a simplified block diagram of the ma\
in logic board. The diagram 
shows the ICs and the buses that connect them together. 
General Information iMac (Flat Panel) Troubleshooting -
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Logic Board, Top 
Note: Enlarge the page to view the graphic at a larger size. 
4 -iMac (Flat Panel) Troubleshooting
 General Information  

Logic Board, Bottom 
Note: Enlarge the page to view the graphic at a larger size. 
General Information iMac (Flat Panel) Troubleshooting -
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I/O Ports

Service Cables 
Three extension cables (076-0897) are required when troubleshooting th\
e iMac with the 
bottom housing open, as shown below. 
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. 
Connect the cables as shown below. 
A= power cable

B= drive data cable

C= blind mate...

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...

4 
Resetting the PMU on the Logic Board 
Resetting the PMU (Power Management Unit) on the logic board can resol\
ve many system 
problems. Whenever you have a unit that fails to power up, you should fo\
llow this procedure 
before replacing any modules. 
1. Disconnect the power cord. 
2	 Remove the user access panel from the bottom of the computer. 
3	 Press the PMU reset switch (shown below) once on the bottom side of th\
e logic board and then proceed to step 3. Do 
NOT press the PMU reset switch a...

Power-On Self Test 
There is a power-on self test that resides in the ROM of the iMac. This \
test automatically runs 
whenever the iMac is powered on after being fully shut down (the power-\
on self test does not run 
if the machine is only restarted). 
If a problem is detected during the test, you will not hear a normal sta\
rtup chime. Instead, the 
system will beep as explained below. Refer to “Error Beeps” later \
in this chapter for instructions 
on how to troubleshoot and repair an iMac that...