Hitachi 46W500 Training page 30

DP-3X AUDIO VIDEO MUTE CIRCUIT EXPLANATION
(See DP-3X 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 I001 outputs V. Mute from pin 49 when changing channels, Auto Programming, etc... This
high is routed to the Video and Audio Mute circuit.
VIDEO MUTE PATH.
The High from pin 49 is routed to D507 to the base of Q529. The following actions will be labeled MUTE ACTI-
VATION here forward, please use the below explanation when Mute Activation is mentioned.
•
MUTE ACTIVATION:
1. When Q529 turn on, the collector pulls the base of Q528 low and turns it on. It's collector is connected
to the HVcc 9.3V line through R5A5 and D510. When Q528 turns on, it's collector goes high. This is
routed to the following circuits. Through R564, D503, and R561 and into the Rainforest IC I501 pin 39.
This pin is also the same pin that FC H Blk and FC V Blk is input. Generally this input is a positive go-
ing pulse that blanks the video during the peak pulses which represent retrace. However, when the DC
component is forced high by the action of Q528 turning on, this pin goes high and mutes the output of
RGB.
2. Another route for the high from Q528 is through D406. This high continues to the PST1 connector on
the Terminal PWB. This turns on QV08 and QV09 which grounds out the Audio Outputs from the
Monitor Out on the Terminal PWB.
3. Another route for the high from Q528 is through R5A1 to the base of Q527. This transistor turns On
and outputs the high from it's emitter to mute the Audio described later.
SPOT:
Another circuit attached to the Mute Activation circuit (Q529 base) is SPOT. This signal is generated from the
deflection PWB when either Horizontal or Vertical deflection is lost. This is to prevent a horizontal or vertical
line from being burnt into the CRTs. See Horizontal and Vertical Sweep Loss Detection circuit and explanation
and circuit diagram for details. This high is input from PPD3 pin (4), through PPS3 pin (4), D511 to the base of
Q529. See the Mute Activation circuit explained previously.
H Blk Loss Det:
Another circuit attached to the Mute Activation circuit (Q529 base) is H Blk Loss Det.
If the Horizontal Blanking signal is loss to the Signal PWB, Q525 will detect the loss. Normally, Q526 is sup-
plied with H. Blanking on it's base. By the activity of the pulse charging C546 and C545, the base of Q525 and
it's emitter are held high keeping it turned off. If H. Blk is lost, then C546 will discharge through R599. C545 is
blocked by D509 and it holds the emitter of Q525 high. This action turns on Q525 and supplies a high through
D508 to the base of Q529. See the Mute Activation circuit explained previously.
AUDIO MUTE PATH: Labeled as V MUTE 2: (Emitter of Q527 Mute Activation Circuit)
See the Mute Activation circuit explained previously as to how Q527 is turned on.
When Mute Activation is turned on, the following circuits are activated.
CRT MUTE PATH: Shown going to the CRT PWB. Labeled as V MUTE 1:
The high from Q527 is routed to PSC pin 11. This high goes to Q856 base. This turns on and supplies a ground
to the following diodes, D853 on the Green CRT PWB, D803 on the Red CRT PWB D8A3 on the Blue CRT
PWB. When the diodes are supplied with a low on their cathodes, they remove the base voltage fro the RGB
drivers, Q853, Q803 and Q8A3 on the Green, Red and Blue CRT PWBs. This shuts off each CRT Drive.
See next page for continuation of Audio Mute Circuit explanation.
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