Apple imac 21 5 inch late 2009 User Manual

							iMac (21.5-inch, Late 2009) — General Troubleshooting 212010-11-18
Diagnostics
Run Apple Service Diagnostic version 3S135 to determine if any thermal sensors or blowers 
are malfunctioning. If ASD is not available, run Apple Hardware Test version 3A189 by holding 
down the D key during startup. When a test reports an error, reseat appropriate connections. 
If issue persists, replace the corresponding part (sensor, blower, logic board, video card, or 
power supply). See Apple Hardware Error code chart below for correlation between error code, 
affected sensor, sensor location, and additional checks to perform.
AHT Error codeSuspected part and 
Location Suggested Action
Notes
4SNS/1/C0000008: 
TA0P - xxx Ambient temp 
sensor damaged or 
disconnected from 
logic board.  Verify sensor cable is 
securely connected to the 
top edge of the logic board 
and attached to the left 
speaker housing. Replace 
sensor cable if damaged. All fans ramp 
at full speed 
if sensor is 
disconnected.
4SNS/1/C0000008: 
T00p-xxx ODD temp sensor 
damaged or 
disconnected from 
logic board. Verify sensor cable is 
securely connected to the 
logic board and the sensor 
is properly attached to the 
ODD mechanism. Replace 
sensor cable if damaged. The ODD fan 
will run at full 
speed if sensor is 
disconnected.
4SNS/1/C0000008: 
TH00--xxx HDD temp sensor 
damaged or 
disconnected from 
logic board. Use the 
correct sensor cable, 
each drive vendor has 
a unique sensor cable. Verify sensor cable is 
securely connected to top 
left side of logic board and 
is connected to hard drive.  
Check for damaged cable 
on logic board. 
The HD fan may 
run at full speed 
if the sensor is 
disconnected. 
4SNS/1/C0000008: 
TL0p LCD temp sensor on 
LCD is damaged or 
disconnected from top 
of logic board Verify that the LCD sensor 
cable is securely connected 
to the logic board and the 
sensor is attached to the 
LCD.  Replace the sensor 
cable if damaged The CPU fan will 
run at full speed 
if the sensor is 
disconnected.
4SNS/1/C0000008: 
TS2P-xxx Skin temp sensor 
(Quad-core models 
only) is damaged or 
disconnected from top 
of logic board. Verify that the skin temp 
sensor cable is securely 
connected to the top 
of the logic board and 
sensor is attached to rear 
housing (near the camera).  
Replace the sensor cable if 
damaged.  
						

							iMac (21.5-inch, Late 2009) — General Troubleshooting 222010-11-18
AHT Error codeSuspected part and 
Location Suggested Action
Notes
4SNS/1/40000000: 
TC0H CPU temp sensor 
(located on back side 
of logic board).  Note: 
this sensor is not 
available as a separate 
service part Check CPU sensor cable 
connection to logic board. 
It requires removal of the 
logic board.
If the sensor is 
disconnected, the 
CPU fan will run 
at full speed.
4SNS/1/40000000: 
TG0H GPU temp sensor 
(located on back side 
of logic board) Check GPU sensor cable 
connection to logic board. 
It requires removal of the 
logic board. If sensor is 
disconnected the 
CPU fan will run 
at full speed.
4MOT/4/40000002: 
ODD-xxx Optical fan/blower
Verify that the ODD 
blower/fan cable is securely 
connected to the right side 
of the logic board and that 
there are no obstructions 
that would prevent the 
blower/fan from rotating. 
Replace fan if the error 
continues. Normal fan 
operation, except 
the ODD blower.
4MOT/4/40000002: 
HDD-xxx Hard drive fan/blower, 
located below logic 
board, near hard drive Verify that the HDD 
blower/fan cable is securely 
connected to the top of the 
logic board and that there 
are no obstructions that 
would prevent the blower/
fan from rotating. Replace 
fan if the error continues. Normal fan 
operation, except 
the HDD blower.
4MOT/4/40000002: 
CPU-xxx CPU fan/blower, 
located next to left 
speaker (logic board 
has to be removed to 
replace CPU blower) Verify that the CPUblower/
fan cable is securely 
connected to the left side 
of the logic board and that 
there are no obstructions 
that would prevent the 
blower/fan from rotating.  
Replace fan if the error 
continues. Normal fan 
operation, except 
the CPU blower.
Note: Make sure 
black mylar tape 
along the bottom 
of LCD panel is 
not obstructing 
fan blades, if so, 
cut tape and re-
stick to LCD.  
						

							iMac (21.5-inch, Late 2009) — General Troubleshooting 232010-11-18
Diagnostic LEDs
Depending on iMac model, there are either three or four built-in diagnostic LEDs on the logic 
board that can help troubleshoot the computer. LEDs are located on bottom right edge of logic 
board (under a piece of black mylar tape) and can only be seen when looking through lower 
vents of rear housing.    
						

							iMac (21.5-inch, Late 2009) — General Troubleshooting 242010-11-18
LED Functions
LED #1 
• Indicates that trickle voltage from power supply has been detected by logic board. This LED 
will remain ON whenever the iMac is connected to a working AC power source. The LED will 
remain on even when computer has been shut down or put to sleep. The LED will turn off 
only if AC power source is disconnected or power supply is faulty.
LED #2
•  Indicates that logic board has detected power from power supply when computer is 
turned on. This LED will be ON when computer is turned on and power supply and voltage 
regulators are working correctly.
LED #3
•  Indicates that computer and video card are communicating. This LED will be ON when 
computer is communicating properly with video card. If LEDs 1 and 2 are ON and you heard 
the startup sound, but LED 3 is OFF, then video card might be installed incorrectly or need 
replacement. Note: LED #3 is not present on models with integrated graphics. 
LED #4
•  Indicates that computer and LCD panel are communicating. This LED will be ON when 
computer is turned on and video signal is being generated. If LED 4 is ON and there is 
no image on display, then LCD panel, LED backlight board, or cables between might be 
installed incorrectly or need replacement.  
						

							iMac (21.5-inch, Late 2009) — General Troubleshooting 252010-11-18
LED Startup Sequence
LED #1 = Power available.  
If no LED is visible:• Verify AC source 
•  Verify known-good AC cable is connected
•  Verify cable connection between AC inlet and power supply
•  Verify cable connection between power supply and logic board
•  Verify power supply
LED #1 + LED #2 = Power available, and system is powered on. 
If second LED is not visible when power button is pressed: • Verify power button connection to logic board
•  Verify power button functionality
•  Verify cable connection between power supply and logic board
•  Verify power supply
•  Verify logic board
LED #1 + LED #2 + LED #3 = Power available, system is powered on, and video card found. 
 If third LED is not visible after power on: • Verify that MXM video card is seated properly
•  Verify logic board
LED #1 + LED #2 + LED #3 + LED #4 = Power available, system is powered on, video card 
found, and internal LCD found.
If fourth LED is not visible after power on: • Verify cable connections between LCD panel and logic board
•  Inspect LCD display cables for cable damage 
•  Verify external video functionality, and according to result check the following items:
         -If external display works then verify/replace LED backlight board 
         -If external display works then verify/replace LCD panel 
         -If external display does not work verify/replace logic board  
						

							iMac (21.5-inch, Late 2009) — General Troubleshooting 262010-11-18
Logic Board Test Points
Test points, which can be used to verify proper power flow, are accessible on logic board when 
LCD panel is removed. All voltages given in Troubleshooting Symptom Charts assume that 
computer is plugged into a known-good power outlet with a known-good AC cable.  Some 
guidelines for using test points: 
• Warning: HIGH VOLTAGE:  Use extreme caution when live testing!
•  Do NOT lean over or touch the power supply area during live testing.
•  Keep your fingers behind finger guards on test probes when measuring.
•  Turn dial of voltmeter/multimeter to measure DC (direct current, usually indicated by a solid 
horizontal line over dashes). If your voltmeter requires a set voltage range, choose a DC 
range that includes the voltage you are measuring.
•  Connect black probe to ground. Connect red probe to test point and verify voltage.
For more info, see kBase #HT3250: Diagnostics: Using a digital multimeter
 
Logic Board Test Point Function
Pin 1 Ground
Pin 4 Standby 12V power (permanent power coming from power supply 
and present as long as AC cable is connected, even if computer is 
off ); corresponds to LED #1
Pin 6 Backlight Control pulse width modulated signal (from logic board 
to LED backlight board, to adjust the backlight level setting 
according to user setup)
Pin 11 12V Run-Mode power to logic board (coming from power supply, 
present as long as system is on or asleep); corresponds to LED #2
Pin 12 Power On Request signal (from logic board to power supply when 
power button is pressed)
Pin 13 Backlight Enable (signal from logic board to Backlight Controller 
board, to enable backlight  
						

							iMac (21.5-inch, Late 2009) — General Troubleshooting 272010-11-18
Sensor and Fan Connector Locations
Ambient temp sensors and fans connectors locations are shown below. Ensure cables are 
correctly routed and the sensors and fans are properly connected. If a sensor or fan is faulty or 
not connected, Apple Hardware Test and Apple Service Diagnostic will generate an error code.  
						

							iMac (21.5-inch, Late 2009) — General Troubleshooting 282010-11-18
Block Diagram
Refer to this diagram to see how modules are interrelated.
SO-DIMM
Antenna
Antenna
AntennaSO-DIMM
Temperature 
SensorTemperature 
Sensor
Fan
MLB
SO-DIMM
Display
AC/DC
Power 
Button
Bluetooth
Speakers
Hard DriveOptical Drive
AC Inlet
T emperature 
SensorCamera
Microphone
Speakers
Backlight
Controller
Fan
Fan
MXM
802.1 1n
Ambient
T emperature 
Sensor
IR Sensor
SD Card Reader
SO-DIMM  
						

							iMac (21.5-inch, Late 2009) Symptom Charts — Startup and Power 29 2010-11-18
Symptom Charts
Follow steps in the order indicated below. If an action resolves the issue, retest system to verify.
Note: A compilation of Quick Check tables is available at:
http://service.info.apple.com/QRS/en/quickreference.pdf
Startup and Power
No Power, Dead Unit
Unlikely cause: speakers
Quick Check
SymptomsQuick Check
No Power, Dead Unit
•  No power
•  No fan spin
•  No startup chime
•  No image on external display
•  No hard drive or optical drive 
activity 1.
  Verify power source.
2.  Verify power cable.
3.   Listen closely for signs of activity from system 
including: rotating fans, hard drive or optical drive 
activity, startup chime, etc.
Deep Dive
Check ResultAction Code
1.   Power ON system. Verify if 
there is any indication that the 
system has powered up (fan 
rotation, hard drive or optical 
drive noise, backlight turns on). Yes
The symptom is powering 
up. Go to Won’t Start Up 
symptom flow.
No Go to step 2.
2.  Locate diagnostic LEDs in 
bottom case vents. Plug AC 
cord into system. Verify if 
diagnostic LED #1 turns ON. 
You may alternately check for 
presence of a 12V DC signal 
between pin 4 and pin 1 of 
logic board. Yes
Standby power voltage being 
supplied by power supply.  
Go to step 3.
No Replace power supply.  
						

							iMac (21.5-inch, Late 2009) Symptom Charts — Startup and Power 30 2010-11-18
3.  Press power button while 
monitoring diagnostic LEDs. 
Verify if LED #2 turns ON and 
remain ON after pressing 
the power button. You may 
alternately check for a power 
request signal between pin 12 
and pin 1 of logic board. YesPower supply functioning and 
logic board detects supply 
voltages. Go to Won’t Start 
Up symptom flow.
No Go to step 4.
4.  Disconnect AC cable then 
remove power supply and 
carefully inspect connectors 
between AC inlet and power 
supply, then DC connectors and 
cables between power supply 
and logic board, for damage or 
poor connections. Yes
Replace damaged part. P16
No Go to step 5.
5.   Inspect power button and 
verify if it is properly connected 
to the logic board. Yes
Go to step 6.
No Reconnect power button.
6.  Disconnect power button from 
logic board. Inspect cable and 
connector for damage. Verify 
continuity between the two 
pins of power button when it is 
pressed. Yes
Power button is functioning 
correctly. Reconnect power 
button to logic board and 
go to step 7.
No Power button faulty. Replace 
rear housing (which includes 
power button). X14
7.   Press power button and Verify 
if system turns ON. You may 
alternately check for presence 
of a 12V DC signal between 
pin 11 and pin 1 of logic board 
when power button is pressed. Yes
Power supply functioning. If 
system still won’t boot, go 
to Won’t Start Up symptom 
flow.
No Replace DC power cable.  
Go to step 8. X03
8.  Press power button and verify if 
system turns ON. Yes
Issue solved with replaced DC 
power cable.
No Replace power supply.  
Go to step 9. P01
9.   Press power button and verify if 
system turns ON. Yes
Issue solved with replaced 
power supply.
No Reinstall power supply and 
replace logic board. M01
Note: If No Power symptom persists after all steps have been followed use minimum 
configuration troubleshooting to proceed. Try disconnecting hard drive, optical drive, AirPort, 
Bluetooth, and SD card modules to determine if one of them is preventing the power supply 
from functioning.