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6-3-2 HORIZONTAL OUTPUT STAGE
The Horizontal Drive Pulse output at pin 26 is pulled up to 12V to drive Q404 and then coupled via T401
to output transistor Q433 for on-off control. Thus saw-tooth current through Horizontal Deflection Yoke is
obtained.
The function of C-correction is to correct the asymmetrical non-linearity of picture. L402 and horizontal
Yoke are in series for C-correction. Pin36 of IA01 provides a voltage which depends on Horizontal
Frequency to control L402 via Q405, thus the inductance of L402 changes according to the Horizontal
Frequency to correct the linearity.
The function of S-correction is to correct the symmetrical non-linear distortion equidistant lines.
C416, C423, C419, C420, C421 are S-correction capacitors, also they block the DC voltage to the Yoke.
C416 is a fixed one; the others are controlled by IA01 via Q417, Q411, Q413, Q415 switches. When any
switch turns on, the accordingly capacitor becomes in parallel with C416. The switches on-off depend on
the Horizontal Frequency. They are:
Horiz. Freq.
C416
Fixed
0.24
C423
controlled
by Q416
0.1(CS0)
C419
controlled
by Q410
0.22(CS1)
C420
controlled
by Q412
0.56(CS2)
C421
controlled
by Q414
1.2(CS3)
70 < fh
d
87kHz
ON ON OFF OFF OFF
65 < fh
d
70kHz
ON OFF ON OFF OFF
58 < fh
d
65kHz
ON ON ON OFF OFF
49.5 < fh
d
58kHz
ON OFF OFF ON OFF
45 < fh
d
49.5kHz
ON OFF ON ON OFF
40 < fh
d
45kHz
ON ON ON ON OFF
36 < fh
d
40kHz
ON OFF ON OFF ON
32 < fh
d
36kHz
ON ON OFF ON ON
d
32 kHz
ON ON ON ON ON
6-3-3 SUPPLY VOLTAGE CONTROL FOR HORIZONTAL DEFLECTION
The B+ control function block is included in I301 which consists of an operational trans-conductance
amplifier, a voltage comparator, a flip-flop and a discharge circuit. Pin 28 of I301 is a drive voltage which
consists of horizontal width, pincushion, and trapezium and pin corner correction information. This
voltage is controlled by IA01 via I
2
C bus. The drive voltage feed into pin15 (BIN) of I301. The operation
frequency of the B+ control block is the same as horizontal frequency. The B+ drive output of the control
block is at pin 28(B.DRV.), this drive voltage switch Q402 on-off via a buffer build by Q400 and Q401.
Q402 act as a step down DC converter to drive horizontal deflection output Q433 via L401. The width,
pincushion, trapezium information are modulated on the DC converter by changing the duty of the B+
drive.
Moreover, the B+ duty is controlled with a charging circuit at same time. When the Q302 is OFF, the
voltage at pin16 of I301 will linearly increase with a charge time of determining by R326 and C308 to
modulate B+ duty.
Horizontal DC centering circuit is build by Q423, Q424. By controlling the small current flow in or out of
L405, it will provide DC center compensation for CDT.
ViewSonic Corporation
16
Confidential – Do Not Copy
A
9
0f+-1
Summary of Contents for A90f+ 1
Page 57: ...12 PCB Layout ViewSonic Corporation 54 Confidential Do Not Copy A90f 1...
Page 58: ...VIDEO PWB 0414 ViewSonic Corporation 55 Confidential Do Not Copy A90f 1...
Page 59: ...KEY CONTROL PWB 0488 ViewSonic Corporation 56 Confidential Do Not Copy A90f 1...
Page 60: ...MAIN BOARD 13 Schematic Diagrams ViewSonic Corporation 57 Confidential Do Not Copy A90f 1...
Page 61: ...VIDEO ViewSonic Corporation 58 Confidential Do Not Copy A90f 1...
Page 62: ...KEY CORTROL ViewSonic Corporation 59 Confidential Do Not Copy A90f 1...
Page 63: ...POWER SUPPLY CKT ViewSonic Corporation 60 Confidential Do Not Copy A90f 1...
Page 64: ...MCU CONTROL CKT ViewSonic Corporation 61 Confidential Do Not Copy A90f 1...
Page 65: ...Time Base DeflectionCKT ViewSonic Corporation 62 Confidential Do Not Copy A90f 1...
Page 66: ...H V DYNAMIC FOCUS CKT ViewSonic Corporation 63 Confidential Do Not Copy A90f 1...
Page 67: ...14 Exploded Diagram ViewSonic Corporation 64 Confidential Do Not Copy A90f 1...