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A sensing resistor inside of TX3201 provides a DC voltage
proportional to the CRT anode voltage and is used like a
primary feedback for the HV compensation circuit. A
secondary winding on TX3201 (pin 6) provides a low
voltage flyback pulse (H-FLYBK) used for synchronization
of the Scan Boost Converter and the HV Compensation
circuit. A capacitive divider, CX3205 and CX3206, provide
a low voltage flyback pulse (H-FBP) used for
synchronization, phase comparison, etc.
The linearity coil L3200 is saturating inductor skewed
by a permanent magnet bonded to the coil. It produces
a non-linear inductance curve vs current. This
characteristic cancels non-linearity in the deflection
current caused by horizontal deflection coil resistance.
BASE DRIVE
(Refer to figure on the next page). The Base Drive
(Proportional Drive) circuit provides high forward and
reverse current to drive the base of the horizontal output
transistor QX3200 from a low level input (H-DRV from
the deflection processor ICX2600 in main chassis). This
signal is approximately 9 Volts peak to peak at the
operating frequency and has a duty cycle of about 40%
high, 60% low.
Current from H-DRV is amplified by transistors Q3203
and Q3204 providing low impedance to rapidly drive
the gate of the driver transistor Q3205. This action results
in an alternating current flow in the primary of driver
transformer T3200. During Q3205 on time energy is stored
in T3200 and rapid turn off of QX3200 is initiated. During
Q3205 off time the energy previously stored in T3200 is
used to drive the base of QX3200. A winding in T3200
from the emitter of QX3200 to ground provides pulse
shaping to optimize the base drive and improve efficiency.
HV COMPENSATION
A resistor inside of the sweep transformer senses the CRT
anode voltage (Pin 14). The DC voltage appearing on
this resistor is used in one of the operational amplifiers
of IC3101 to provide the error voltage needed to regulate
the HV to a specified level.
The error voltage is compared with a ramp signal
generated in one comparator of IC3100 and sinchronized
by the flyback pulse (H-FLYBK) at horizontal scanning
frequency to modulate the pulse width in the output to
drive the gate of the switching transistor Q3103. This
ramp signal is present only during the flyback pulse.
Q3103 is on during the scan time and as long as the
error voltage is higher than the ramp signal. This allows
energy to be stored in TX3100. When Q3103 is turned
off, the resonant circuit formed by C3109 and the primary
inductance of TX3100 produce a flyback voltage of about
400 volts peak resulting from the stored energy in
TX3100.
PV154 - 923-03497
SERVICING
This voltage is induced to the secondary windings of
TX3100 to add to the voltage generated in the horizontal
deflection circuit. This induced voltage is used to
compensate load variation (beam current variation) in
the HV flyback transformer TX3201. RX3335
(potentiometer) is used to adjust the high voltage to a
specified level. (Refer to the figure on the next page).
SHUTDOWN CIRCUIT OPERATION
(Refer to figure on the next page). 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 forms a DC voltage appearing
on C3001 representative of the CRT anode voltage (HV)
produced by TX3201. This voltage is divided down by
precision resistors RX3001, RX3002, and RX3003. This
lower voltage appears on the positive input (pin 5) of
IC3101. In the event the CRT anode voltage becomes
excessive, in IC3101 the positive input (pin 5) will be
higher than negative input (pin 6) and therefore this
output (pin 7) will go to high level at approximately 15
volts. This signal (SD-DRV) is sent to the base of Q3201
causing the horizontal drive to be disabled and latched
causing HV to goe down. In about 5 seconds the
shutdown reset circuit (Pins 8, 9 & 14 of IC3100) enables
the horizontal drive and HV must be reestablished. If
the shutdown condition persists, 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).
VERTICAL DEFLECTION
(Refer to figure on the next page). The vertical deflection
circuit (ICX2100) is a linear amplifier that can directly
drive the yoke current (including the required DC
component). The sawtooh waveforms needed as inputs
by ICX2100 are generated in the Deflection Processor
ICX2600. V-PROT is an image of vertical deflection current
and it is used by the Deflection Processor to protect the
CRT.
3-4
AB - SERVICING
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