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11. Fan Operation
Chapter 11 - Fan Operation
The fan is turned on when the TV is powered ON and blows air out of the TV. The TV will only shutdown when
the power supply (thermistor) reaches a critical temperature (set in the service mode), not if the fan stops.
Fan Operation
The fan runs at one of three speeds based upon the temperature of the power supply board. The power supply
board temperature is monitored by a thermistor that feeds IC6 (not shown). The output voltage of this thermistor
circuit at CN 1/pin 4 is a linear function of the temperature. 0 degrees C = 0Vdc. 100 degrees C = 4.7Vdc.
The Main CPU on the B board monitors the fan’s rotation and run voltage. This fan status is available as an OK
or NG indication in the user menu and service mode. In addition, the service mode displays the power supply
temperature. If the power supply temperature reaches critical (92 degrees for the 32" TV or 80 degrees for the
42" TV), the Main CPU discontinues the CPU_GO and RDP_GO signals and the TV shuts down. After shutdown,
the Standby light repeatedly blinks three times to indicate that high temperature was the cause of shutdown.
FAN
IC11
PS3
T2
25 26
1
24
FAN
DRIVE
MAIN
CPU
IC21,IC22
CONTROL
6
1
2
3
5
6
DRIVE
GND
CN3009
CN3005
13V
CN7
CPU_GO
CN1/
CN1203
FAN
DET
FAN
FB
CN3003/
CN1001
CN2
RDP_GO
FIGURE 11-1 - FAN DRIVE
2TVP13 1432
4/16/02
Q BD.
4
ROTATION
= 0V
*THERMO
THERMO
5V
CN1
0V=0 C
0.8V=21 C
4.7V=100 C
0V
8.6V
*
TV SHUTS
DOWN WHEN CN1/
PIN4
RISES TO:
4.3V-32" (92 C)
3.76V-42" (80 C)
PLASMA
PANEL
B BD.
POWER SUPPLY BD.
6
5
7
5V
18k
5V
Fan Drive Voltage
When the TV is turned ON, the Main CPU (B board) outputs 5Vdc (CN1001/pin 24) to the fan drive block at
CN1001/pin 24. This allows the fan drive block (Q board) to output 12Vdc (connector CN3009/pin 1) to the run
the fan at start up. A run voltage from 8 to 12Vdc will always be present as long as the TV is ON.
Fan Rotation Detection
Within the fan, a Hall device detects rotation and grounds the voltage at CN3009/pin 2. This LOW is applied to
Main CPU and permits the temperature of the power supply board to adjust the Main CPU fan drive output
voltage. Typically at start up, the fan drive voltage at CN1001/pin 24 drops from 5Vdc down to 1.5Vdc to produce
8.6Vdc at CN3009/pin 1 to run the fan at slow speed.
Troubleshooting No Fan Rotation
If the fan is unplugged or there is no fan rotation detected, Main CPU reacts by turning ON the Fan drive signal
(CN1001/pin 24) to 5Vdc every two seconds (for a very short time; that may be difficult to detect except on a peak
reading DVM). This results in 12-volt fan run voltages that appear at the fan terminals (CN3009/pin 1) every two
seconds as long as the TV is ON.