Zenith C32V23 - 32" Flat-Screen Integrated HDTV, Service Manual

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PV154 - 923-03497 AB - SAFETY ii
PRODUCT SAFETY SERVICING GUIDELINES FOR AUDIO-VIDEO PRODUCTS
X-RADIATION
To prevent possible exposure to x-radiation caused by excessive CRT
Anode voltage, the AB Chassis incorporate a “High Voltage Shutdown”
circuit. This circuit senses the level of flyback pulse from the “Flyback
Transformer” representative of the actual high voltage on the CRT anode.
When this level exceeds a predetermined voltage, the circuit shuts down
the horizontal drive, preventing further generation of anode voltage. In
this condition, the horizontal drive is “latched” off for about 5 seconds,
after which, restart is attempted.
SHUTDOWN CIRCUIT OPERATION
The flyback pulse voltage from Pin 6 of TX3201 (Flyback Transformer) is
peak detected (rectified) by the action of diode D3000 and capacitor
C3001. This form a DC voltage appearing on C3001 representative of the
CRT anode voltage (HV) produced by T3201. This voltage is divided down
by precision resistors RX3001, RX3002, & RX3003. This lower voltage,
appear on the positive input (pin 5) of IC3101.
If the even CRT anode voltage become excessive, in IC3101 the positive
input (pin 5) will be higher than negative input of pin 6 and therefore
his output (pin 7) will go to high level, at approximately 15 volts. This
signal (SHUTDOWN) is send to Base of Q3201 causing Horizontal Drive to
be disabled and latched causing HV goes down. In about 5 seconds, the
shutdown reset circuit (Pins 8, 9 & 14 of IC3100) enable again the
Horizontal Drive and HV must be reestablished. If the shutdown condi-
tion persist the circuit goes into hiccup mode.
The circuit formed by Q3104, C3113, C3108, D3107, R3131, R3132, R3133
and R3134 disable the HV compensation output (Q3102-B signal) during
turn on and shutdown conditions (transients).
CRT ANODE HIGH VOLTAGE MEASUREMENT PROCEDURE
Each CRT screen size has it’s own safe operating anode and shutdown
voltage. Critical safety component (designated with an ‘X’ in the compo-
nent designator) are designed to operate the CRT at a safe operating
anode voltage and provide proper shutdown thresholds. If replacement
of any of these components are deemed necessary, it is important to use
original type Zenith components. After replacement is made, confirm
proper anode voltage using the following procedure.
Measurement of the CRT anode voltage must be performed using a high
impedance-high voltage meter, with no raster on the screen, and operat-
ing at nominal horizontal frequency, 33.75 Khz (HDTV signal).
After discharging the CRT, connect a high impedance-high voltage meter
to the CRT anode. Turn the television ‘on’ and confirm a good signal is
being displayed. Reduce Brightness and Contrast settings until the
picture is well extinguished.
Observe the anode voltage meter reading and compare with the table
below for the proper CRT screen size. If the voltage reading is higher
than the maximum, verify circuit component values and proper opera-
tion.
CRT Screen
Size
Nominal Anode
Voltage (KV)
Max. Shutdown
Voltage (KV)
32” 30 ± 0.5 36
36” 30 ± 0.5 36
34” Wide 30 ± 0.5 36
CRT Anode Voltage
HV SHUTDOWN PROCEDURE
Adjust beam current to 0 mA. Connect a variable Resistor (10 MW)
between pin 2 and pin 3 of 2W6 connector, and decrease slowly the
resistance value from 10 MW to 0 W. Measure shutdown HV. Increase the
resistance value to 10 MW. After 5 seconds, approximately, verify that
the HV must be reestablished (High Voltage Reset).
Components and Factory Menu registers with any influence in HV in-
crease.
• C3109
• C3115
• CX3204
• CX3208
• CX3210
• L3200
• RX3335
• TX3100
• 40 Vcd
• H_SIZE REGISTER