Hitachi 43FWX20B, Тренировка, Страница: 60 / 154

DP-2X AUDIO VIDEO MUTE CIRCUIT EXPLANATION
PAGE 03-16
(See DP-2X Series Chassis Audio Video Mute Circuit Diagram for details)
There are times in which the main picture and audio must be muted. This can be because of changing channels
where the noise between stations is unacceptable, same thing for Auto Programming channels. When the deflec-
tion circuit malfunctions, etc…
All this is done primarily to prevent damage to the CRTs or to external amplifiers or speakers connected to the
projection television.
MICROPROCESSOR OUTPUT:
The Microprocessor outputs V. Mute from pin 49 when changing channels, Auto Programming, etc… This high
is routed to the Video Mute circuit and to the Audio Mute circuit.
VIDEO MUTE PATH.
The High from pin 49 is routed to D412 to the base of Q442 . The following action will be labeled MUTE ACTI-
VATION for here forward, please use the below explanation when Mute Activation is mentioned.
MUTE ACTIVATION:
When Q442 turn on, the collector pulls the base of Q441 low and turns it on. It’s collector is connected to the
HVcc 9V line through R551 and D411 . When Q441 turns on, it’s collector goes high. This is routed to two
places. Through R441 , D402 , and R439 and into the Rainforest IC pin 24 of I401 . This pin is also the same pin
that FC H Blk and FC V Blk is input. Generally this input is a positive going pulse that blanks the video during
the peak pulses. However, when the DC component is forced high by the action of
Q411 turning on, this pin goes
high and mutes the output of RGB.
The other route for the high from
Q411
is through
R548
to the base of
Q440
. This transistor turns On and outputs
the high from it’s collector out it’s emitter to mute the Audio described later.
Another circuit attached to the
Mute Activation circuit is AC Loss Detection.
AC LOSS DETECTION:
AC is monitored by the AC Loss detection circuit. The AC input from I903 to PPS3 pin ( 1 ) on the Power Supply
PWB is routed and rectified by D416 . This charges up C561 and through D415 to charge C467 . When AC is first
applied, C467 charges slightly behind C561 preventing activation of Q445 . If AC is lost, C561 discharges rap-
idly pulling the base of Q445 low, however D415 blocks C467 from discharging and the emitter of Q445 is held
high. This action turns on Q445 and produces a high on it’s collector. This high is routed to the base of Q442 .
See the Mute Activation circuit explained previously.
SPOT:
SPOT is generated from the deflection PWB when either Horizontal or Vertical deflection is lost. This is to pre-
vent a horizontal or vertical line from being burnt into the CRTs.
See Horizontal and Vertical Sweep Loss Detec-
tion circuit and explanation and circuit diagram for details. This high is input from
PPD2
pin (
4
), through
PPS2
pin ( 4 ), D413 to the base of Q442 . See the Mute Activation circuit explained previously.
H Blk Loss Det:
If the Horizontal Blanking signal is loss to the Signal PWB, Q444 will detect the loss. Normally, Q444 is sup-
plied with H. Blanking on it’s base. By the activity of the pulse charging C466 , the base of Q443 and it’s emitter
are held high. If H. Blk is lost, then C466 will discharge through R558 . C465 is blocked by D414 and it holds the
emitter of
Q443
high. This action turns on
Q443
and supplies a high to the base of
Q442
. See the Mute Activa-
tion circuit explained previously.
See next page for continuation of Audio Mute Circuit explanation.