McIntosh MC-420 Service manual
-CONTENTS
Performance
Notes
Block
<i>
Interconnection Diagram
<!>
Electronic Parts List
<|>
Power Supply
<|>LED
<§>
Preamplifier
<|>
Outputs
<^
Equalizer
<j>
Assembly Views
Specifications
Diagram
-
7-£
9-10,
11-12,
2
2
3-4
4-5
5-6
11-12
8, 12
11-12
13-16
17-19
20-22
Mclntosh
Laboratory Inc. a Chambers
Street
Binghamton.
New
York 1 3BO3
Printed
in
U.S.A.
Part
No.
O-4O275
Performance
Specifications
POWER
output
ohm
RATED
TOTAL HARMONIC DISTORTION
from
DYNAMIC HEADROOM
FREQUENCY
INPUT SENSITIVITY
OUTPUT
Minimum
loads, 4 Channel Mode
20Hz
Maximum
250
1.3dB
+ 0,
+ 0,
0.3V
sine wave continuous
per
channel,
POWER
to
20kHz
harmonic
milliwatts
RESPONSE
-0.25dB
-S.OOdB
to 2
Volts
BAND
from
from
all
to
20Hz
10Hz
channels operating,
50
Watts.
distortion
rated power
to
20kHz
to
50kHz
average
at
any
output
power
into
4
power level
.005%
A-WEIGHTED,
110dB
(2V)
DC
INPUT VOLTAGE
14.4
Volts
CURRENT
Idle
Rated
LOAD
2
ohms
DIMENSIONS
Width
Height
Depth
CONSUMPTION
- 2.0
amps
Power
STABILITY
(mm)
(mm)
(mm)
SIGNAL-TO-NOISE
- 31
amps
14.25"
2.75"
12.00"
(362)
(71)
(305)
RATIO
Notes
1.
The
heavy lines
primary
2.
Unless otherwise noted,
the
following conditions:
a.
b.
c.
3.
Unless otherwise specified:
a.
b.
c.
4. The
voltages
signal
jacks.
signal path.
schematics
DC
input
ON
connector
All
voltages
ground, unless otherwise specified. A high
impedance
used.
Resistor
Capacitor values
Inductor values
voltages enclosed
that
connected
on the
are
at
14.4 volts.
at
14.4VDC.
are
±10%
(10
megohm) voltmeter must
values
are in
are in
are in
are
measured with a 0.3V,
to all
schematics denote
all
voltages indicated
measured under
with
respect
ohms.
microfarads (uF).
microhenries (uH).
in a box are
channels
at the
the
on
the
to
be
signal
1kHz
input
5. On PC
Indicates:
a.
b.
c.
6.
WARNING:
Parts
characteristics.
recommended
Board Drawings, Square
Polarized Capacitors - Positive
Diode - Cathode
Others
- Pin 1
.
marked
with
Use
by the
the
Pad
symbol
ONLY replacement parts
manufacturer.
ZlA
have
critical
EQUALIZER
EQUALIZER
CHANNELS
HI-PASS FILTER
SUBWOOFER
LEVEL
(45Hz)
(150Hz)
4
EXT
(4) 3V
FLAT
FLAT
OUT
POWER
GUARD
^
ATTENUATOR
d
P^
PREXX^
^
_
LEVEL 1 "-•
|
^
HI-PASS
FILTER
U,
OUT
120
—
i
BO
11-PASS
FILTER
—^
—^
ATTENUATOR
•
ATTENUATOR
POWER
GUARD
ATTENUATOR
POWER
GUARD
POWER
GUARD
d
d
r~
""''
1
LEVEL 2 •"-!
^N.
r-
^RE
J^>
I
LEVEL 3 »J
»
1
EQUALIZER
*—
HI-PASS
FILTER
HI-PASS
FILTER
HI-PASS
FILTER
u.
^
OUT
*^ — I
1
20
RLTER
OUT
'^'
eo
*
120
FILTER
OUT
"^—
eo
L—
120
FILTER
HI-PASS
1
HI-PASS
|
Hl-PASS
i i ^
r
r
"H
CHANNELS
^
SUB
WOOFER
FILTER
1
^
*"*i
CHANNELS
I"
^
^
E"1
EXT
exr
-*~J
'^
SUB
1
SUB
|
i
SUB
Block
Diagram
Interco
SUBWOOFER
O1S°
i
WARNING:
shaded
area
Use
ONLY
ed
by the
DC
POffifl
e
Parts
located
have critical characteristics.
replacement
manufacturer.
/
parts
in the
recommend-
below
BK
POWER
Output
-OJBOB
ne-
'e
AMPLIFIER
Supply
J20
PE
LEO
^^
EQUALIZER
i.
EQ
IN 1
2.
GND
3.
EO
IN Z
4.
EQ
IN 3
S.
E.
EQ
IN
4
7.
B.
EQ OUT 4
9.
15V
10.
EB
11.
NC
IS.
EQQJT
13.
-16¥
14. ES
OUT
OUT
M
3
2
1
OOOOOOO
ooooooo
\terconnection
Diagram
ZER
(ST3
UT
2
1.
PBEOUT
S. WO
3.
PHEOUT
4. GND
3.
PflEOUT
.
GND
.
PREOUT
?
O O
O O
O O
O O
O O
O O
O 1O
J
S
3
4
a. PA IN 4
9. 15V
10. PA IN 3
11. 5V
12. PA IN 2
13.
-15V
14. PA IN 1
O O
O O
O O
O O
O O
O O
O
lO
INTERCONNECTION
PARTS
LIST
Symbol
CIRCUIT
CB1
CONNECTORS
TB1
MISCELLANEOUS
MT1
BREAKERS
088018
OS
Part
117541
1008
©
CD
Jia
©
©
J14
>
©
Jll
©
©
J10
>
©
Description
CB,
DC
Fan,
35A
Input
12V,
4©
40
-
OUTPUTS
3©
3©
BO/120
(5UBWOCFER)
3/4
-INPUTS
1/2
ON
PG
2©
20
-OUTPUTS
1©
10
Terminal
1.9W
Power
Symbol
No.
C1,
3,4,6,7,9,
010,12,14,42,
043,44,45,46,
C48.49
C13,15,47,86,
C94,431,432,
C433.434
016,17,18,19
C21,
22,23,39,
40.56,62,69,
C71,
75,166,
C171,435,437
C24,25,26,28,
030,31,32,33,
C34,35,36,37,
C38,119,122,
C251.252
C29
C41
C53,59,60,200
057,106,107,
0108,109,110,
0111,112,113,
0114
067,68,100,
0137,139,140,
0142,144,145,
0146,148,150,
0152,153,157,
0158,162,172
078
079,163,436
085,138,151,
0154,155,159,
0160,250
091
0101
0123,124,128,
C132
0125,126,130,
0133
0127,131,135,
0136,500,501
0156,161
0168
0300,301,302,
C303
C421
0423,424
0429,430
01,2,3,4,7,9,
010,12,13,14,
016,17,18,19,
020,21,23,24,
025,26,27,28,
029,31,32,33,
034,39
D5,6
08
D35
D36
D37
038
DS1
DS2
Amplifier
CF
RES 5% 1
Part
No.
066445
066447
061011
061248
064320
064312
064325
061150
061159
066446
064302
066448
066437
066327
061106
061206
064308
061196
066457
066254
061199
061249
066441
066439
070047
070150
070114
070041
070131
070148
070149
058115
058078
ELECT
ELECT
DISC
DISC
M
POLY
M
POLY
M
POLY
CERAMIC
CERAMIC
ELECT
POLY
ELECT
ELECT
ELECT
DISC
DISC
.0047mF
DISC
ELECT
ELECT
DISC
.47uF
ELECT
ELECT
SIG
ZN
10V
ZN
16V
RECT
RECT400V
RECT
RECT
LED
LED
/8W
ARE NOT
LISTED
Description
10mF50V
100mF
16V
15pF
10% NPO
.1mF
24V Y5T
.047uF
5%
100V
.01uF
100V
5%
.1uF
5% 63V DC
.1mF
+80
-20%
.01
mF
+80
-20%
47mF
35V
.0015uF
5%
63VDC
3.3mF
50V NP
10mF
50V LOW ESR
470mF
10V
.OOlmF
10%
220pF
20% Z5F 50V
5% 63V
47pF
20%
N470
50V
100uF
50V
220mF
25V
100pF
10%
Ml
500 50V
50V
MONOLITHIC
2200uF
25V
3300uF
35V
75V
150mA
1N4148
5%
500mW
5%
500mW
100V
3A
1N5401
1A
1IM4004
FMG32R
FMG32S
Yellow,SLP-444B...SA
Red
SLP144B
DC
.50V
50V
Qty.
16
9
4
14
17
1
1
4
10
18
1
3
8
1
1
4
4
4
2
1
4
1
2
2
28
2
1
1
1
1
1
1
1
Electronic
Parts
List
3ty.
16
4
14
17
1
1
4
10
18
1
2
2
28~
IC11.13
1015,22
IC16
IC37
J1
J2
J10.11,
12,
J14
13,
L1,3
L4,5,6,7
01,2,3,4
05,23
06,83,84,85,
O86
O8.92
011,17,36,38,
039,40,45,46,
047,48,49,54,
055,56,58.61,
087,88,90,91
019,20,21,32,
037,44,53,57.
063,65,66
024,25,34,51
026,41,43,52
033,35,42,50
060,89
064
067,74,75,79
068,72,76,80
094,95,96,97
098,201,202,
0204
099,200,203,
0205
R1,
14,21,
29
R4,
11,
18,25
R3,12,19,26
R5,10,17,24
R28,46,124
R30.45
R42,
68,198,
R900
R62.63.64.65
R76.89.159,
R162.180
R109
R132
R148,160,601,
R602,700,701,
R702.703
R173.178
R200
R205
R206,225,231,
R233
R21
1,216,229,
R350
R223,224,232,
R234
R237
R238,239,240,
8241,242,243,
R244.245
133239
133250
133253
133197
117449
117527
117522
122293
122297
132193
132263
132257
132171
132224
132223
132233
132262
132261
132172
132090
132239
132238
132260
132231
132232
144333
144330
144329
144331
144316
144334
141165
134465
144328
144313
144317
144332
144333
141170
141051
137033
137074
137050
141381
141204
Dual Voltage
010..
5V
Regulator
-5V
PWM
Phono Jack
CONN
.SA
Regulator
Controller,
Header
Amp
MC78M05CT...MO
MC79M05CT...MO
6P
14 POS
Terminal Block
Choke
Output Choke
N
JFET
2N4392
PNP
2SB892
NPN
2SC3792
NPN
MPSA05
PNPMPS4126
NPN
MPS4124
NPN
2SC3423
NPN
2SC2705
PNP2SA1145
PNP
MPSA55
NPN DAR
MPSA25
PNP2SA1302
NPN
23C3281
FET
MTP50N05E
NPN
2SC3298B-0
PNP2SA1306B-0
MF
2Kohm
1%
MF
100K
ohm
1%
MF
9.53K
1%
1/8W
MF
16.5K
ohm
MF4.99K
MF
CF
Gain
MF
MF 1 1K
MF
MF931
MF2Kohm
CF
CF
FLAMEPROOF
FLAMEPROOF
FLAMEPROOF
CF56
CF
ohm
2.32K
ohm
10
ohms
5%
Control
20K
14.3K
1%
ohm 1%
53.6Kohm
ohm
1%
1%
100 ohm 5%
1.2Kohm
5%
ohm 5% 1W
2.2 ohm 5%
1/8W
22 ohm 5%
IK
100 ohm 5%
STK350-
TL598QN
Gold Plated
1/8W
1/8W
1%
1/8W
1%
1/8W
1%
1/8W
1/2W
ohm
1/8W
1%
1/8W
1/8W
1/8W
1/2W
1/4W
ohm 5%
1/2W
1/4W
1/4W
1/4W
WW
2
2
1
1
1
1
5
2
4
4
2
5
2
20
R247,248,250,
R252
R254.255.256,
R257
RT1.2
S1,2,3
T1
Symbol
C1,3,6,8,10,
C12,14,16
C2,4,5,7,9,11,
C13.15
C17
C18.19
IC1.2
11
4
4
4
2
1
4
4
4
4
4
4
4
4
4
3
2
4
4
5
1
1
8
2
1
1
4
4
4
1
8
J1
S1,2
139196
134470
144279
148062
159244
Equalizer
CF
RES 5% 1
No.
Part
No.
064320
064325
066437
061248
133260
117526
148062
.22 ohm 5% 5W
POT
220 ohm
Thermistor
Slide
100 ohm
Switch 4P3T
Power
/8W
ARE NOT
Description
M
POLY
.047uF
M
POLY
.1uF
5% 63V DC
ELECT
10mF
50V LOW ESR
DISC
CAP
.ImF
Dual
Op-Amp
BA
CONN
Socket
14 POS
Slide Switch 4P3T
LISTED
5%
100V
25V Y5T
15532
DC
4
4
2
11
1
Qty.
8
8
1
2
2
1
2
2>>Power
1
1
1
MT1+
/s
>BO-
1
1
CB1
//
TB1
TB1
(RD)
(BK)
BK<1>
J205
,
DC' I -KM
T
1
(
MTl-
]v
J50-2
1
(
ON
>J14-3
1
•BJ
1
Supply
PC
BOARD
POWER
SHEET
1
oaJa
JT
V7^.
1 OF
B7;
1.*
14.3V
OS
{
B
4V 1
i
-I
13
AMPON
ON 3 13.8V
i/
•R100
^W*
=
R237S
C200
A
14V
g
?
R114
A
15k T
DC-V
-\7
DC-
5V
RfOJ'
Z.3C
FAN
CONTROL
/%|\V
R111;
>
1-011
ov
.7V
/PS
ff^OVER
V,
VOLTAGE
10
048205
SUPPLY SECTION
3
6
>
>
i
14.4V
.
13.6V
3/P
VJS,
SHITCH
2
14.3V
12V
8200
DC-
T T
V
oo.V
J+MO
2200
14.4V
NOTE:
SHORT
TP1 AND TP2 TO
SPEAKER PROTECTION,
TROUBLE
SHOOTING
DEFEAT
WHEN
UNIT.
RBW<
4.7k<
J-C1BB
T .1
1
-IBv
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