![background image](http://html1.mh-extra.com/html/viewsonic/a90f-1/a90f-1_service-manual_1020116020.webp)
6-3-4 TIMEBASE CONTROL (I301), VERTICAL
The vertical free running frequency is determined by C312 (pin 22 of I301). The amplitude of the output
at pin 23 can be adjusted via Icon.
Icon provides a DC shift at the saw-tooth output at pin 23 and the EW drive output EWDRV (pin24)
in such a way, that the whole picture moves vertically while maintaining the correct geometry.
6-3-5 VERTICAL OUTPUT STAGE
The power amplifier driving the vertical yoke assembly is a DC design-based on power amplifier I310
TDA8172.
The vertical deflection coil is connected to pin5 of I310 via P401A.
The saw-tooth signal is derived from Pin 23 of I301 and fed to pin1 of I310 via R306. The DC bias voltage
is derived from pin13 of I301 and fed to pin7 of I310 via derived R325 / R327 to optimize the vertical
position.
There are two supply voltages for I310, -15V is applied at pin4 via R384, +15V DC voltage is applied
through R386 to pin2 and pin6 for the output stage during the retrace time. The supply voltage for the
output stage during the retrace time is derived from the fly-back generator output at pin3 of I310 and
applied through C388 to pin6.
6- 4 HIGH VOLTAGE GENERATOR AND BLANKING CIRCUIT
I101 is a current mode PWM controller which provides the drive signal for high voltage generator. It is
synchronized by horizontal blanking signal coming from deflection circuit via Q111. Q121, Q124 are high
voltage output switches. T101 provide the high voltage (25.9KV) to CDT anode. Pin13 of T101 provides
feedback to pin2 of I101 to control the duty when high voltage is varied according to the beam current.
Thus it gives a very good high voltage and size regulation. A very precise geometry distortion is achieved.
R176 provides high voltage adjustment.
Pin5 of T101 senses high voltage for OVP protection. When high voltage is over 33kV, it raises the emitter
voltage of Q114 to the degree that is 6.8V higher than Q115 collector, Q116 start to conduct and shutdown
the PWM (I101) by reducing the voltage at pin1.
Pin 8 of FBT senses the beam current. When beam current rise, base voltage of Q126 drop and so the
emitter does. The voltage across C108 drops to pull down the voltage at pin15 of I901 (PWB-0414). When
voltage at pin15 of I901 drops under 6V, contrast of display start to decrease. R167 set the light output
where the contrast (or full white screen light output) start to drop. If the beam current is too high, Q118 will
conduct and shutdown PWM controller (I101).
Pin7 of FBT provides negative bias for Grid1 of CDT.
Pin5 of I310 provides vertical blanking to base of Q108 via D113. Q108 collector pulse gives a proper
blanking level at Grid 1 of CDT. When monitor turns off, pin3 (H.UNLOCK) is pull high to turn off Q108 via
D108. Grid 1 of CDT is then pulled down to most negative voltage from pin7 of FBT to protect CDT.
ViewSonic Corporation
17
Confidential – Do Not Copy
A
9
0f+-1
Содержание A90f+ 1
Страница 57: ...12 PCB Layout ViewSonic Corporation 54 Confidential Do Not Copy A90f 1...
Страница 58: ...VIDEO PWB 0414 ViewSonic Corporation 55 Confidential Do Not Copy A90f 1...
Страница 59: ...KEY CONTROL PWB 0488 ViewSonic Corporation 56 Confidential Do Not Copy A90f 1...
Страница 60: ...MAIN BOARD 13 Schematic Diagrams ViewSonic Corporation 57 Confidential Do Not Copy A90f 1...
Страница 61: ...VIDEO ViewSonic Corporation 58 Confidential Do Not Copy A90f 1...
Страница 62: ...KEY CORTROL ViewSonic Corporation 59 Confidential Do Not Copy A90f 1...
Страница 63: ...POWER SUPPLY CKT ViewSonic Corporation 60 Confidential Do Not Copy A90f 1...
Страница 64: ...MCU CONTROL CKT ViewSonic Corporation 61 Confidential Do Not Copy A90f 1...
Страница 65: ...Time Base DeflectionCKT ViewSonic Corporation 62 Confidential Do Not Copy A90f 1...
Страница 66: ...H V DYNAMIC FOCUS CKT ViewSonic Corporation 63 Confidential Do Not Copy A90f 1...
Страница 67: ...14 Exploded Diagram ViewSonic Corporation 64 Confidential Do Not Copy A90f 1...