Hitachi 51F510, Manual

Page: 39 / 152

DP-4X AUDIO VIDEO MUTE CIRCUIT EXPLANATION
PAGE 02-07
(4) AC LOSS DETECTION:
AC is monitored by the AC Loss detection circuit. The AC signal generated from PC101 photo coupler on the
Power Supply PWB to the connector PPS1 pin ( 10 ). This signal is routed and rectified by DY08 . This charges up
CY93 and through DY08 to charge CY92 . When AC is first applied, CY92 charges slightly behind CY93 pre-
venting activation of
QY47
. If AC is lost,
CY93
discharges rapidly through
RZE0
pulling the base of
QY47
low,
however DY08 blocks CY92 from discharging and the emitter of QY47 is held high. This action turns on QY47
and produces a high on its emitter. This high is routed through DY07 and to the base of QY57 . See the Mute Ac-
tivation circuit explained previously.
V MUTE 2 CIRCUITS: ( Emitter of QY42 the Mute Activation Circuit ):
The following explains the circuits affected when the Mute Activation Circuit is turned on.
CRT MUTE PATH: (
Labeled as V MUTE 1 on CRT PWB ):
The high from QY42 is routed to PSC pin 11 . This high goes to Q856 base. This transistor 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 for the
RGB drivers,
Q853 , Q803 and Q8A3 on the Green, Red and Blue CRT PWBs. This shuts off each CRT Drive.
FRONT AUDIO OUT HARD MUTE PATH:
•
The high from QY42 (the Mute Activation Circuit) is routed to DA04 . The high continues to the base of
QA10 . When this transistor turns on, it supplies a Lo to pin 11 of IA02 and hard mutes the Audio Out.
(Note: This is not the same thing as the Mute selected from the customer’s remote. This is controlled by
the Front Audio Control IC
IA01 internally and functions in three states, No Mute = 100%, 1/2 Mute =
50% and Full Mute = 0%.
FRONT AUDIO IC RIGHT and LEFT INPUTS MUTE PATH:
The high from QY42 (the Mute Activation Circuit) is routed to DA01 . The high continues to the bases of QA07
and QA08 . When these transistors turn on the ground the Audio Front Right and Left signal input to the Audio
Output IC IA02 and pins 4 and 2 .
MONITOR and OUT TO HI-FI MUTE PATH:
The high from QY42 (the Mute Activation Circuit) is also routed to the anode of D407 and then to the cathodes
of
D405
and
D406
. This high then arrives at the bases of
Q409,
and
Q411
. When these transistor turns on they
ground the Right and Left audio for the Monitor Out and Out to Hi-Fi audio output jacks J402 .
FRONT AUDIO OUT MUTE:
Labeled as V MUTE 1 (From Microprocessor Pin 49)
V MUTE 1: The high from the Microprocessor pin 49 to I010 (in pin 3 at 3.3V and out pin 17 at 5V). This
High is sent to the following 4 circuits:
1. To the Front Audio Out Hard Mute circuit routed through
DA06 . ( Described above )
2. The high is also routed through DA03 to the base of QA01, and QA02 . When these transistor turns on,
they ground the audio going into the Audio Output IC IAA1 at the PPS4 connector. Right audio in pin 2
of the
PPS4
connector to pin
4
of
IAA1
. Left audio in pin
3
of the
PPS4
connector to pin
2
of
IAA1
.
3. CRT Mute: See CRT Mute Path explanation above.
4. Out to Hi-Fi Mute Path: The high from the Level shifter I007 pin 13 is routed to the anode of DA53
and then to the cathodes of
DA51
and
DA52
to the base of
QA51,
and
QA54
. When these transistor
turns on, they ground the audio going into the audio for Out to Hi-Fi audio output jacks.
(Continued on page 8)