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 boot to Mac OS X. 
2.	Bluetooth is available via the external USB Bluetooth adapter (sold separately). 
3.	The new service parts for the 15” 800 MHz model are: 
• 661-2841 Board, Logic, 800 MHz, Ver. 2 
• 661-2803 Hard Drive, 3.5”, 60GB 
• 661-2806 Drive, DVD-ROM/CD-RW (Combo), 32X 
What’s New and Different (2002): 
1.	Important:  The logic board has 3 thermal pads on the bottom side of the logic board. These pads must 
be changed each time the main logic board is removed from the bottom housing. Failure to replace these 
pads may cause the microprocessors to overheat and become damaged. (An exception would be if you 
are simply testing the logic board and only detach it for a few minutes.) 
Refer to the Take Apart chapter, “Thermal Pad Installation”. 
2.	Important:  The CPU uses a thermal pipe to transfer heat away. This pipe has a thermal connection to 
the top metal chassis (Faraday cage). This connecting point must be cleaned and have new thermal 
paste applied to it 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 the bottom housing to be removed. 
Refer to the Take Apart chapter, “Thermal Paste Application”. 
3.	Important:  The bottom plate has 4 screws that must be tightened to at least 17 in.-lbs. If you do not 
have a torque driver, you will have to make sure these bolts are firmly tightened (by hand or purchase the 
service tool (076-0899) in order to ensure the thermal pipe is firmly mated with the top base. If the 
bottom plate is not securely attached to the base in this fashion the CPU may overheat and become 
damaged. 
4.	Special service tools are required to perform some procedures. A service stand, 076-0898, to hold the 
unit during take apart and service cables, 076-0897, that allow the unit to run while the bottom housing is 
open.  Important:  Diagnostic service cables allow the unit to run while the bottom housing is open; 
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. 
5.	The CPU is now G4 based, running at speeds of 700 MHz and 800 MHz. 
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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 port supports external digital audio speakers. 
11. There are three USB ports on the iMac (Flat Panel); previous iMac models had two USB ports. 
12. The iMac (Flat Panel) houses a different A/C power cord; power cords from older iMac models will not  fit into the A/C socket. 
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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. 
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Logic Board, Top 
Note: Enlarge the page to view the graphic at a larger size. 
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Logic Board, Bottom 
Note: Enlarge the page to view the graphic at a larger size. 
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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 connector

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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. The PMU \
reset button is located 
on the right side of the board, refer to the logic board diagram below. \
Location of the PMU Button 
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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 second time because it could crash the 
PMU chip. 
WAIT ten seconds before connecting the power cord and powering the compu\
ter on. If the 
computer powers on, go to the next step. If the computer does not power \
on, there is 
something else wrong with the computer, refer to the symptom/cure, “N\
o Power” in this 
chapter. 
5. Run MacTest Pro and return the computer to the customer. 
Note: This entire procedure resets the computer’s PRAM. Be sure to reset t\
he computer’s time, 
date and other system parameter settings before returning the computer t\
o the customer. 
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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 sounds error beeps at sta\
rtup time. 
Following is a definition of what the error beeps at startup time signif\
y. 
One Beep: No RAM is installed or detected. 
Two Beeps: Incompatible memory is installed. (The iMac ships with PC-133 SDRAM). \
Three Beeps: No RAM banks passed memory testing. 
Four or Five Beeps: Bad checksum for the remainder of the boot ROM. The ROM is bad. 
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