CTX EX-710F, Service Manual

Page: 10 / 101

4.0 DESCRIPTION OF CIRCUIT
CFA1797B
4.0 DESCRIPTION OF CIRCUIT
1. Power supply circuit
The AC voltage input connected to EMI circuit
and rectifier circuit. R102, R112 and Switch
(SW101) will provide DC voltage to IC101,
when switch on. While IC101 works normal,
The IC101 will Auto-detect output voltage of
power supply from Pin2 and correct the duty
cycle of Pin6 output pulse to compensate the
variation of output voltage.
The output of IC101 Pin6 connected to power
MOSEFET to drive the power transformer
T101. When power MOSFET is on, the energy
stored in the primary winding of T101. Once
MOSEFET is off, the energy transfer to the
secondary and charges the output capacitor to
get the stable DC voltage.
2. Oscillation circuit
The functions H-size, H-phase, V-size, V-
center, Side-pin, Parallel….are designed inside
into IC301. The Pin25 is X-RAY protect input.
When H.V output circuit is abnormal (H.V too
high) the X-RAY protect circuit will shut off the
horizontal output, H.V. also will be shut down.
The Pin28 is B + control driver output. The
Pin26 is horizontal square wave output drives
horizontal output. The Pin24 is parabolic
output. The Pin23 is vertical output. The Pin1
& pin2 are H-SYNC & V-SYNC input. The Pin3
is vertical blanking output. The Pin 20, 22 for
vertical oscillator. The Pin 6, 8 for horizontal
oscillator.
3. Vertical output circuit
The Pin23 of IC301 is vertical sync output
connected to IC201 (Amplifier), Pin5 of IC201
is vertical amplifier output drives the vertical
deflection directly.
4. Horizontal output circuit
The DC-DC is to generate a DC voltage (B
+
)
for horizontal output circuit. The CPU (IC501)
controls the H. size adjustment function of
IC301 via the I 2 C Bus. The output of IC301
(Pin6) connected to gate of Q311 to make the
Q311 switching. When Q311 is ON, the
energy stored in T304 and the energy released
via D313 when Q311 turned OFF. The B +
applied to Horizontal Yoke and supply the
power for horizontal deflection. The more the
B + will get the bigger the horizontal size.
5. Micon circuit
The IC501 (CPU) will detect polarity and
frequency of input H.V. Sync. The CPU will
determine the mode of input timing (preset or
users mode) and load mode data from IC502
(EEPROM). The outputs of IC501 were
connected to other function circuit (IE. H-size,
H-phase, V-size, and V-center…). Also, the
user can adjust picture from keyboard and the
data will be saved into IC502 automatically.
For the O.S.D. mode, when O.S.D. manual is
active CPU will inform the O.S.D IC (IC603) to
send O.S.D BLK signal to blank the video
signal from VGA card, and the O.S.D. IC will
send O.S.D. R.G.B. Video signal to show the
O.S.D. manual on screen.
6. H.V. regulation circuit
The IC401 is a P.W.M IC; Pin6 is P.W.M
output, which connected to Q407, Q409. The
Q402 is H.V. output switching transistor. Q401
and D401 are damper device provide the path
of damper current. Q421 is a feedback voltage
from FBT Pin13 connected to PIN2 (IC401)
and correct the duty cycle of PIN6 output pulse.
7. Video output circuit
Video circuit consists of video preamplifier
IC601 and output cascade amplifier IC604.
IC601 is a video processing IC equipped with
three DC amplifiers to pre-amplify R.G.B.
signals from 0.7V to 4.2V.
The R.G.B. GAIN & BIAS control signal are
from IC501 via I 2 C-bus to DAC IC601. The
IC601 control to video gain. The output of pin
24, 25, 26 are connected to BIAS circuit of
each R.G.B. signal’s amplification and thus
achieve a well balance able white picture.
The O.S.D. R.G.B. (Pin4, 9,13 of IC601) is the
input of O.S.D. Video signal. The IC604 is
R.G.B. drive to capable of driving CRT.
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