S-DV990SW
37
5
7
8
5
7
8
C
D
F
A
B
E
7. GENERAL INFORMATION
7.1 DIAGNOSIS
7.1.1 PROTECTION CIRCUIT
Note: Refer to the Schematic Diagram about the actual circuit.
(The
&
number corresponds to the marked circuits.)
1
Protection circuit when the Speaker terminal
becomes overloaded
Q3601
Q3602
Q3603
B
E
C
+5V
D3351
C3605
0.1
D3601
R3351
0.1
R3601
4.7k
R5527
270k
R108
27k
Front L ch
to
XPROTECT
GND FL
R3353
1.8k
R3355
33k
B
A
VD+5
+
POWER Assy
D
6CH AMP Assy
C
(DVD/CD TUNER)
CONTROL Assy
In Normal mode, the speaker (6 ohms) is connected between the
FL and GND FL points. Because the voltage at Point
A
is higher
than that at Point
B
, Q3601 does not operate.
If the resistance between the FL and GND FL points becomes
1.83 ohms or less, Q3601 begins to operate, Q3602 is turned on,
Q3603 (E, C, and B)is turned on, and the level of XPROTECT
becomes MID.
→
The microcomputer detects the XPROTECT level and
shuts the power to the unit off.
B
A
C101
(C102)
1/50
+
to
XPROTECT
(
µ
-com)
6CH AMP Assy
C
R108
27k
R101
(R104)
1k
R102
(R105)
10k
R103
(R106)
10k
R109
820
D105
(D106)
Q102_1/2
(Q104_1/2)
Q102_2/2
(Q104_2/2)
Q101_1/2
(Q103_1/2)
Q101_2/2
(Q103_2/2)
D101
(D102)
VD+5
VD+5
VH+
(VP+15)
VH–
(VA–12)
2
-1 Short-circuit-detection circuit for the amplifier
power circuit (VH+[VP+15], VD+5, -12 V [VA-12])
Circuit for shutting the power off when VP+15, VD+5, or VA-12
is short-circuited to ground (GND)
2
-2 Short-circuit-detection circuit for the DVD power
Line (VP+8)
XPROTECT
TUNER
6CH AMP Assy
C
VD+5
R108
27k
D104
1SS355
Q106
DTC124EUA
Q107
DTA124EUA
VP+8
• In Normal mode, as Q101 (Q103) (E2, B2, C2) and Q102
(Q104) (E2, B2, C2) are on, the voltage at Point
A
is about 5 V.
The voltage at Point
B
is therefore about the same. As Q101
(Q103) (E, C, B) is off, Q102 (Q104) (E, C, B) is also off.
(1) When VH+(VP+15) is short-circuited to GND
As the voltage at Point
B
becomes almost ground potential, and
Q101 (Q103) (E, C, B) then Q102 (Q104) (E, C, B) are turned on,
the level of XPROTECT becomes low.
→
The microcomputer detects the XPROTECT level and shuts
the power to the unit off.
(2) When VH-(VA-12) is short-circuited
As the electric potential of VE at Q102 (Q104) (E2, C2, B2)
becomes the same as that at VB, Q102 (Q104) (E2, C2, B2) is
turned off. Following this, Q101 (Q103) (E2, B2, C2) is turned
off, which changes the voltage at Points
A
and
B
to a value other
than 5 V. Therefore, Q101 (Q103) (E, C, B) then Q102 (Q104) (E,
C, B) are turned on, the level of XPROTECT becomes low.
(3) When VD+5 is short-circuited
The level of the XPROTECT line becomes low. The
microcomputer detects the XPROTECT level and shuts the power
to the unit off.
C
C
E
E
B
B
B2
B2
E2
E2
C2
C2
As the TUNER line is fixed to GND level, Q107 is always on. If
the level at VP+8 falls to GND level because of short-circuit, etc.,
Q106 is turned on, and the level of the XPROTECT line becomes
low.
←
The microcomputer detects the XPROTECT level and shuts
the power to the unit off.
* ( )means the wiring No. of VP+15 line.
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