Yamaha Mg12.4 Service Manual

							21 MG12/4
MG16/4
 14
						

							22 MG12/4
MG16/4
4. Side Cover
(Time required : About 5 minutes each.)
4-1. Remove the bottom cover. (See procedure 2)
4-2.
Side Cover L :
4-2-1. Remove the rack mount angle L. (See procedure 1)
4-2-2.Remove the screw marked [430A], three (3) screws
marked [430B], three (3) screws marked [440A] and
two (2) screws marked [450A]. The side cover L can
then be removed. (Fig. 2)
4-3.
Side Cover R :
4-3-1. Remove the rack mount angle R. (See procedure 1)
4-3-2. Remove the PS circuit board. (See procedure 3)
4-3-3.Remove the screw marked [430C], three (3) screws
marked [430D], three (3) screws marked [440B] and
two (2) screws marked [450B]. The side cover R can
then be removed. (Fig. 2)
PS[470]Spacer
(Fig. 1-1) [470]: Bind Head Tapping Screw-S 3.0 x 6 MFZN2W3 (WE877900)Heat sink
(Photo 1)
[B] IC01 IC02 IC03IC05 Q01 [B] [A] [A]
PS
PS
3-5. Remove the three (3) screws marked [B]. (Photo 1)
3-6. Remove the solder IC02, IC03 and Q01. The heat sink
can then be removed from the PS circuit board. (Photo 1) w
						

							23 MG12/4
MG16/4(Fig. 2) [430]: Bind Head Tapping Screw-S 3.0 x 6 MFZN2B3 (WE877800)
[440]: Bind Head Tapping Screw-S 3.0 x 6 MFZN2W3 (WE877900)
[450]: Hex. Socket Set Screw-S 3.0 x 6 MFZN2B3 (WF419300)
[460]: Bonding Tapping Screw-B 3.0 x 10 MFZN2B3 (WE878000)
Side cover RSide cover L
[440B]
[440B]
[440B][440A]
[440A]
[440A] [450A]
[450A] [450B]
[450B] [450C]
[450C]
[430B]
[430B] [430B] [430D]
[430D] [430D]
[460] [460]Fader knobs
Hexagonal nuts
Hexagonal nuts
[430C]
MIX
[430A]
Volume knobs
MAIN
MAIN
JACK
2/2
JACK
1/2JACK
1/2
5. MAIN Circuit Board, Jack 1/2, 2/2 Circuit
Board 
(Time required : About 15 min.)
5-1. Remove the bottom cover. (See procedure 2)
5-2. Remove the rack mount angle L and R.
(See procedure 1)
5-3. Remove the PS circuit board. (See procedure 3)
5-4. Remove the side cover L and R. (See procedure 4)
5-5. Pull out the fourteen (14) fader knobs. (Fig. 2)
5-6. Remove the two (2) screws marked [450C]. (Fig. 2)
5-7. Remove the twenty-six (26) screws marked [460] and
thirty-four (34) hexagonal nuts. The MAIN and JACK
1/2, 2/2 circuit boards can then be removed. (Fig. 2)
Disconnect the nine (9) connectors and separate the
MAIN circuit board and the JACK 1/2 circuit board.
* The knobs, buttons and supporting fixtures on the MAIN
circuit board are not components of the circuit board.
When replacing the MAIN circuit board, be sure to
remove these parts according to the following
procedure.
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							24 MG12/4
MG16/4
[420] [420] [420] [420] [420]
Push HPF buttons
Hooks
Hexagonal nuts
MIX1 support (upper)
MIX1 support (lower)
Push PFL buttons
Meter cover
Push HPF buttons
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Push HPF buttons
MIX2 support
Sleeve ON buttons
Push PFL buttons
[420]: Bind Head Tapping Screw-S 3.0 x 6 MFZN2W3 (WE877900)
(Fig. 3)Meter reflector
MAIN
JACK
2/2
5-8. Remove the hexagonal nut. The JACK 2/2 circuit board
can then be removed from the MIX1 support. (Fig. 3)
5-9.Pull out the eighty-nine (89) volume knobs from the
MAIN circuit board. (Fig. 2)
5-10. Remove the twelve (12) push ON buttons, twelve (12)
sleeve ON buttons, thirteen (13) push PFL buttons and
thirty-seven (37) push HPF buttons from the MAIN
circuit board. (Fig. 3)
5-11. Remove the five (5) screws marked [420]. The MIX2
support can then be removed from the MAIN circuit
board. (Fig. 3)
5-12. Twist the eight (8) hooks of the MIX1 support (upper)
to become straight, and the support can be removed from
the MAIN circuit board. (Fig. 3)
 * The upper and lower MIX1 support each can then be
removed in the same manner.
5-13. Detach the meter cover from the meter reflector.
(Fig. 3)
Push ON buttons
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							25 MG12/4
MG16/4
6. Power Switch and AC Connector
(Time required : About 6 minutes each.)
6-1. Remove the rack mount angle L and R.
(See procedure 1)
6-2. Remove the bottom cover. (See procedure 2)
6-3. Remove the PS circuit board. (See procedure 3)
6-4. Remove the side cover R. (See procedure 4)
6-5. Remove the power switch by bending its claw.
(Photo 2)
6-6. To remove the AC connector, remove the hexagonal nut
and flat washer. (Photo 2)
(Photo 2)
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							26 MG12/4
MG16/4

 IC BLOCK DIAGRAM
NJM2068M-D(TE2) (X3505A00)
Dual Operational Amplifier
MG12/4 MAIN, MG16/4 MAIN: IC502, 503, 
        IC702, 703, 902-904, ICA02-04, 
        ICB01-03, ICC01-03, ICD01-03,
        ICE01, 03, ICF01, ICG01-05
MG16/4 MAIN: IC102, 103, 302, 303
NJM4556AL (XP844A00) 
Dual Operational Amplifier 
MG12/4 MAIN, MG16/4 MAIN: ICH03
NJM4580ED (XT157A00)
Dual Operational Amplifier
MG12/4 MAIN, MG16/4 MAIN: IC501, 601, 
        IC701, 801, 901, ICA01, ICE02, 
        ICF02, ICG06, 07
MG16/4 MAIN: IC101, 201, 301, 401
1
2
3
4-V8
7
6
5
Output A+V
Non-Inverting
Input A
-DC Voltage Supply+DC Voltage
Supply
Output B
Inverting
Input B
Non-Inverting
Input B Inverting
Input A+-
+-
1
2
3
4-V8
7
6
5
Output A+V
Non-Inverting
Input A
-DC Voltage Supply+DC Voltage
Supply
Output B
Inverting
Input B
Non-Inverting
Input B Inverting
Input A+-
+-
LB1412M (X5838A00)
LED Driver
MG12/4 MAIN, MG16/4 MAIN: ICH01, 02
13
10
9
8
16
765 43 2 23 2221 20 191817 14 15 12
11
+
-
+
-
+- +- +- +- +- +- +- +- +- +- +- +-
OSC
CURENT
DRIVER
CURENT
DRIVER
VZ
OUT2RESET OSC ILED
D1
D2
D3
D4
D5
D6
D7
D8
D9
D10
D11
D12 IN2
OUT1
IN1
VCC
GND
R
S
Q
R
S
Q Q
R
S
Q Q
R
S
Q Q
R
S
Q Q
1A2345678OUT
A-IN
A+IN
A+IN
B-IN
BOUT
B -V +V
-+B-+
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							27 MG12/4
MG16/4
to MAIN-CNF01
to Power switch, AC connector
: not installed

 CIRCUIT BOARDS
MG12/4 MAIN (X6346C0) ................................. 34/36
MG12/4 JACK 1/2 (X6353B0) ............................... 38
MG12/4 JACK 2/2 (X6353B0) ............................... 37
MG16/4 MAIN (X6345C0) ................................. 28/30
MG16/4 JACK 1/2 (X6254B0) .......................... 32/33
MG16/4 JACK 2/2 (X6254B0) ............................... 33
PS (X6343B0) ........................................................ 27
Note : See parts list for details of circuit board conponent parts.Component side
PS Circuit Board
PS: 2NA-WE61240
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							28 MG12/4
MG16/4
GAIN
HPF
HIGH
MID
LOW
AUX1
PRE
AUX2
PA N
ST
PFL
1-2
1 2 3 4 5 6 7 8 9/10 11/12
PAN/BAL PAN/BA
PEAK PEAK PEAK PEAK PEAK PEAK PEAK PEAK PEAK PEAK
to JACK 1/2-CN171 to JACK 1/2-CN371 to JACK 1/2-CN571 to JACK 1/2-CN771 to JACK 1/2-CN971 to J
A
A
MG16/4 MAIN Circuit Board
MAIN: 2NA-WE52160 
						

							29 MG12/4
MG16/4
0 11/12 13/14 15/16
BAL PAN/BAL BAL BAL STST
C-R/PHONES AUX2 AUX1
AUX2
TO ST
ST/
GROUP
AUX1
ST GROUP 1-2
PHANTOM
+48V
2TR IN
RETURN SEND
2TR IN
PEAK+5
+3
+1
0
-1
-3
-5
-7
-10
-15
-20 LSTR
12POWER
PEAK
2-CN971 to JACK 1/2-CNA71 to JACK 1/2-CND71 to JACK 1/2-CNE71 to JACK 1/2-CNG71 to PS-CN02
to JACK 2/2-CNH02
A
A
Component side
MAIN: 2NA-WE52160
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							30 MG12/4
MG16/4

MG16/4 MAIN Circuit Board
B
B
MAIN: 2NA-WE52160