McIntosh Power Amplifier MC303, Service Manual

Page: 10 / 36

13 14
3
CONTROL
750886 SCH
22
.1
k
R3
47
.5
k
R
2
9
10
8
U1:3
4
5
6
U1:2
4.
75
k
R6
+5VBU
4.
75
k
R1
+5VBU
J8:5
J8:4
FP ON
FP OFF
FR
O
M
D
IS
P
LA
Y
PC MET
PC IN
J9:3
+5VBU
.1
uF C3
TURN ON
CONTROL
10
uF
C1
1
3
1
2
G
D
S
Q4
AMP MUTING
M
UT
E
TURN ON DELAY
2.21M
R11
1u
F
C8
9
10
8
U2:3
1M
R16
.2
2u
F
C1
2
1
2
3
7
B+
GND
14
U2:1
+5VBU
3
1
2
Q1
3
1
2
Q2
.1
uF
C2
15
0k
R1
0
4
5
6
U2:2
12
13
11
U2:4
AC DETECTOR
+5VBU
+5VBU
.1
uF
C1
3
10
0k
R1
4
3
1
2
Q9
22
.1
R2
9
+15V +15V
3
1
2
Q13
10
k
R2
4
3
1
2
Q
8
CONTROL
OUTPUT
10
0
k
R2
5
POWER
4.
75
k
R3
0
3
1
2
Q12
+15V
2.21k
R28
.1
uF
C1
4
47.5k
R22
-24V
5
PC OUT
TO
C
H
3
IN
P
U
T
FR
O
M
C
H
3
IN
P
U
T
1
1
1
BLU
GRN
BLU
1.1A
t
R4
.0
47
uF
C1
3
1
2 IN OUT
U4
33
00
uF
C
4
2
3 1 IN OUT
U3
.1
uF
C
9
10
0u
F
C
7
.1
uF
C1
0
33
00
uF
C
5
10
0u
F
C
6
D2
D3
D1
D4
-15V
+15V
J4
J5
J6
1.1A
t
R5
1 2
HS1
1 2
HS2
P
W
R
T
R
A
N
S
FO
R
M
E
R
S
E
C
O
N
D
A
R
Y
10
0k
R7
-24V
1
2
3
7
B+
GND
14
U1:1
12
13
11
U1:4
22
.1
k
R8
47.5k
R9
+5VBU
METER LIGHT
CONTROL
+5VBU
5
GND J9:5
J9:4
9
PWR RLY
9
GND
5
5
9
9
J8:6
J8:9
J8:8
J8:2
-15V
+15V
9
9
+15V
-15V
+5VBU 9
+5VBU
9
MET
LIGHTS
J8:3
J8:7
J8:1
9
MUTE
MUTE
TO
D
IS
P
LA
Y
J8:10
J8:11
J8:12
9
ILLUM
J8:13
J8:14 J8:15
J8:16
J8:17 J8:18
J9:1
5
GND
5V
0V
0V 5V
-18V
0V
5V
5V
5V
12V
0V
12V
5V
J9:2
-18V
5V
0V
T4