ViewSonic P90F Service Manual download pdf (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:

CS4 CS3 CS2 CS1 CS0

MCU Pin 32 17 18 19 20

Capacitor C425 L406 C421 C420 C419 C423

Hf <32KHz ON OFF ON ON ON ON

32KHz<Hf<=36KHz ON OFF ON OFF ON OFF

36KHz<Hf<=40KHz ON OFF ON OFF OFF OFF

40KHz<Hf<=45KHz OFF ON ON ON ON ON

45KHz<Hf<=52KHz OFF ON OFF ON OFF ON

52KHz<Hf<=58KHz OFF ON OFF ON OFF OFF

58KHz<Hf<=65KHz OFF ON ON OFF ON ON

65KHz<Hf<=70KHz OFF ON OFF OFF ON OFF

70KHz<Hf<=86KHz OFF ON ON OFF OFF ON

86KHz<Hf<=96KHz OFF ON ON OFF OFF OFF

Hf>96KHz OFF ON OFF OFF OFF OFF

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

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ViewSonic P90F Service Manual Page 21