Cambridge Audio Azur 740A Amplifier
AP19799/6 P
reamp PCB Circuit Diagram (P
rotection Circuitry )
Relay
Gnd
Clean
Gnd
R82
1k
1/8W
Metal
Film
Fo
r
1
mA
R71
100R
1/8W
Metal
Film
D
GND
5
6
7
U13:B
LM393AP
D
ual Co
mparato
r
D8
1N4148
Signal D
io
d
e
+5V
Senses a D
C
resistance of 2 ohms or less
D9
Rect
ifi
er
Di
od
e
1N4004
PIC
VI/Sho
rt
R Speaker Test
D
GND
+5V
R Speaker Test
Speaker A Relay
UNR
EG
POWER
AMP
STAND
BY
UNR
EG
D
GND
1
2
3
CN8
3W
a
y
Straight Header
R70
2W
Carbo
n
220R
PIC
D
C
PIC
Clip
PIC
VI/Sho
rt
PIC
Temp
Preamp Standby
Mains Fail
1
2
3
4
5
6
7
8
9
10
CN3
10
Way
Straight Header
To
PIC
6SHDNHU
&DEOH
6KRUW
&LUFXLW
'HWHFWRU
3
2
1
8
4
U14:A
LM393AP
D
ual Co
mparato
r
1
2
3
4
5
CN7
5W
a
y
Straight Header
D
GND
PIC
VI/Sho
rt
PIC
D
C
PIC
CLIP
Temp Sense
R144
1/4W
Metal
Film
10k
+5V
PIC
Temp
R65
910R
1/8W
Metal
Film
910
/
(910
+
1
0k
)
w
ith
ZP221A501E
vo
ltage
gives
100deg
C
c
uto
ut
+5V
Temp Sense
R72
4k
7
1/8W
Metal
Film
R74
10k
1/8W
Metal
Film
R68
4k
7
1/8W
Metal
Film
Open
Collector
Output
R69
100k
1/8W
Metal
Film
D
GND
+5V
L Speaker Test
R80
1k
1/8W
Metal
Film
Fo
r
1
mA
R81
10k
1/8W
Metal
Film
R75
100R
1/8W
Metal
Film
R73
4.7R
1/8W
Metal
Film
3
2
1
8
4
U13:A
LM393AP
D
ual Co
mparato
r
+5V
R64
4k
7
1/8W
Metal
Film
(Open
Collector
Output)
D10
Rect
ifi
er
Di
od
e
1N4004
L Speaker Test
Speaker B
R
elay
RC5
Bl
ock
RC5 TX
To
ne D
efeat Relay
Head
Phones
D
etect
5
6
7
U14:B
LM393AP
D
ual Co
mparato
r
Speaker A Relay
Speaker B
R
elay
C112
100nF
50V
Mo
no
Ceramic
C58
Mo
no
Ceramic
100nF
100V
D
GND
D
GND
1
2
3
4
5
6
CN1
6W
a
y
Straight Header
Head Pho
nes D
etect Gnd
PIC
GND
PIC
IR
o
n/o
ff
1
2
3
4
5
6
7
CN9
7W
a
y
Straight Header
C21
100uF
16V
Electrolytic
D
GND
+5V
D14
1N4148
Signal D
io
d
e
PIC
VI/Sho
rt
R29
4k
7
1/8W
Metal
Film
(Open
Collector
Output)
C7
100uF
16V
Elec
tro
lytic
C6
Mo
no
Ceramic
100nF
100V
C63
10nF
50V
Ceramic
3
URWHFWLRQ
6
LJQDOV
7R$
PS
3,
&
6
LJQDOV
6
SHDNHU
3&
%
6
LJQDOV
3,
&
6
LJQDOV
0DL
QV
3&
%
6
LJQDOV
C51
100uF
16V
Elec
tro
lytic
D
GND
C54
100uF
16V
Elec
tro
lytic
D
GND
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