BBK DV718SI, Service Manual

Page: 32 / 120

3. Working principle of power-off quieting:
Shown in the figure
205 - Q210,
switch pipe is saturated, noises that produce in the course of power off is bypassed to ground, that is
power off quieting function is realised.
4. Key point voltage (unit: V) is shown as the following table:
3.2.11.1, when the player is working normally, D204 is on, +5V charges
capacitor Tc235 through D204, now voltage of Q214 emitter electrode is lower than that of base
electrode, Q214 cuts off. When power off, +5V disappears, base electrode of Q214 changes to low level,
And the emitter electrode changes to high level due to discharge of TC235, now Q214 is on, Q214
collector electrode (AMUTE) outputs high level to add to base electrode of switch pipe Q
Key point E F G H I J K L M
No mute 2.5 3.2 0.7 0.12 -0.15 -4.27 -4.27 4.9 4.9
Mute 3.2 -3.86 -3.87 1.4 0.7 1.3 -4 4.9 4.9
3.2.12 Power circuit
1. Power circuit block diagram is shown as in the following figure 3.2.12.1:
Figure 3.2.12.1 Power circuit block diagram
2. Working principle
(1) Power grid filtering circuit: various electromagnetic radiation exists in surroundings, so it will
produce interference to the inputted AC power, and the function of power grid filtering circuit is to filter
these interference to make those that enter bridge rectification circuit are pure 220V AC power.
T
ra
n
s
fo
rm
e
r
Rectification
Absorption loop
Power grid
filtering
P
ro
te
c
to
r t
u
b
e
Power socket
Switch IC
Feedback
winding
Photoelectric
coupling
TLV
431
Sampling
circuit
Rectification
Filtering
+9V
LED+5V
+5V
+3.3V
-21V
Rectification
Rectification
Rectification
Rectification
Rectification
Filtering
Filtering
Filtering
Filtering
Filtering
FL-
FL+
VIPER22A
Filtering
HOST GND
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