ViewSonic P90F Service Manual page 21

8-3-2 HORIZONTAL OUTPUT STAGE
The horizon. drive pulse output at pin 26 is pulled up to 12V to drive Q404 and then coupled via
T401 to output transistor Q403 for on-off control. Thus saw-tooth current flow through Horizon.
Deflection Yoke is obtained.
The function of C-correction is to correct the asymmetrical non-linearity of picture. L402, L406
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, C425 are S-correction capacitors, also they block the DC
voltage to the Yoke. C416 is the fixed one, the others are controlled by IA01 via Q417, Q411,
Q413, Q415, and Q418 switches. When any switch turns on, the accordingly capacitor is in
parallel with C416. The switches on-off depend on the Horizontal Frequency.
L406 is controlled by pin32 as well, when Horizon. freq. is over 40kHz , L406 is parallel with
L402.
They are:
CS
Rf
MCU Pin
Capacitor
Hf <32KHz
32KHz<Hf<=36KHz
36KHz<Hf<=40KHz
40KHz<Hf<=45KHz
45KHz<Hf<=52KHz
52KHz<Hf<=58KHz
58KHz<Hf<=65KHz
65KHz<Hf<=70KHz
70KHz<Hf<=86KHz
86KHz<Hf<=96KHz
Hf>96KHz
8-3-3
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. This voltage is controlled by IA01 via IIC bus. The drive voltage feed into pin 15
(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(BDRV), this drive voltage
switch Q402 on-off via a buffer build by Q400 and Q401. Q402, act as an step down DC
ViewSonic Corporation
CS4
32
C425 L406
ON OFF
ON OFF
ON OFF
OFF ON
OFF ON
OFF ON
OFF ON
OFF ON
OFF ON
OFF ON
OFF ON
17
CS3 CS2
17 18
C421 C420
ON ON
ON OFF
ON OFF
ON ON
OFF ON
OFF ON
ON OFF
OFF OFF
ON OFF
ON OFF
OFF OFF
Confidential – Do Not Copy
CS1 CS0
19 20
C419 C423
ON ON
ON OFF
OFF OFF
ON ON
OFF ON
OFF OFF
ON ON
ON OFF
OFF ON
OFF OFF
OFF OFF
P90f-1