Yamaha Mg12.4 Service Manual

							41 MG12/4
MG16/4
2-7. Frequency Characteristics
In the signal routes of the Table 2-6-1 to 2-6-6 indicated with q to !0 , the 20Hz and 20kHz frequency response of each output
shall be within the range of 0 dB +1/-2.5 dB compared to the 1kHz (0dB).
* The 20Hz level when the GAIN volume is Max shall be within the range of 0 dB +1.0/-4.5 dB compared to the 1kHz (0dB).
* In the route q, check every OUT when the signal is fed to CH1, and check only the ST L OUT when the signal is fed to CH2
and other channels.
* In the route r, check only the ST L OUT and the ST R OUT.
2-8 HPF
In the state of the Table 2-6-1 and 2-6-2, feeding 80 Hz -36dBu signal, and setting the GAIN to MIN, the STEREO L OUT level
obtained when the /—
80 switch is set to ON shall be within the range of -3 dB +2/-2 dB compared to the level obtained when the
switch is set to OFF.
2-9 Channel Equalizer Characteristics
In the state checked in 2-2 above, check the output level obtained at GROUP 1 OUT in the case of CH INPUT and ST CH
INPUT L and at GROUP 2 OUT in the case of ST CH INPUT R when LO, HI and MID of INPUT are moved respectively. Its
level of each frequency shall be within the range specified in the table 2-9-1 compared to the output level obtained when the EQ
gain control is center click position.
If it is without the range, search the frequency, within the range of +/- 20%, of that the level is within the range of Table 2-9-1.
Table 2-9-1 [dB ]
EQ control EQ GAIN Applied frequency Variation width
HIMAX
10kHz+12 +/- 2
MIN -12 +/- 2
MIDMAX
2.5kHz+15 +/- 2
MIN -15 +/- 2
LOMAX
100Hz+12 +/- 2
MIN -12 +/- 2
Table 2-6-4 Input Terminal STEREO IN [dBu ]
INPUT AUX1 C-R OUT
INPUT INPUT CH
LevelST L OUT ST R OUT GROUP1 GROUP2
PRE OFF PRE ONAUX2
*2
PHONE JACK
9L, 11L (13L, 15L)-30 +4 +/- 2—+4 +/- 2—+3 +/- 2 -7 +/- 2 +3 +/- 2 0 +/- 2
10R, 12R (14R, 16R)—+4 +/- 2—+4 +/- 2 +3 +/- 2 -7 +/- 2 +3 +/- 2—
PIN JACK
9L, 11L (13L, 15L)+4 +/- 2———— ———
10R, 12R (14R, 16R)—+4 +/- 2—— — ———
Table 2-6-5. Input Terminal RETERN L, R [dBu ]
INPUT INPUT Level ST L OUT ST R OUT AUX1 OUT AUX2 OUT
L/MONO
0+16 +/- 2 +16 +/- 2 +15 +/- 2 +15 +/- 2
R—+16 +/- 2 +9 +/- 2 +9 +/- 2
Table 2-6-6. Input Terminal 2TR IN L, R [dBu ]
INPUT INPUT Level ST L OUT ST R OUT C-R OUT L C-R OUT R PHONES L PHONES R
L
-27.80 +/- 2—0 +/- 2—-11.5 +/- 2—
R—0 +/- 2—0 +/- 2—-11.5 +/- 2
* In measuring the C-R OUT L/R and PHONES L/R level, set the C-R/PHONES Output and Meter Select switch to 2TR IN.
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							42 MG12/4
MG16/4
2-12. Meter LED lighting check
PEAK LED lights up, when ST output level reaches +17.5 +/- 2dBu.
0 LED lights up, when ST output level reaches +4 +/- 2dBu.
Operate the fader and check that LED light up in order from “-20” to “PEAK”.
2-13. Distortion Factor
In the signal routes of the Table 2-6-1 to 2-6-6 indicated with q to !0  (except e r), set the VR and Fader of INPUT and and
MASTER to the Nominal Position, and set the GAIN to the position specified in the Table (except PHONES).
Then, feeding each 20Hz, 1kHz and 20kHz signal, the distortion shall be less than 0.1 % when the output signal level is
+14dBu.
At the C-R OUT (L/R), setting the Level Control to the 12 o’clock position,feeding each 20Hz,1kHz and 20kHz signal, the
distortion shall be less than 0.2 % when the output signal level is +3dBu.
* In the route q, check every OUT when the signal is fed to CH1,and check only the ST L OUT when the signal is fed to CH2
and other channels.
* In the route w, turning the PAN/BAL control to L fully, the distortion shall be less 0.1 %, when the ST L OUT signal level
is +4dBu.
* In the route r, check only the ST L OUT and the ST R OUT.
2-14. Maximum Output
In the state 2-2, the distortion factor shall be less than 1% when the output level is +24dBu at ST L OUT and ST R OUT, and
+20dBu at GROUP1/2, AUX1 OUT, AUX2 OUT and C-R OUT.
The distortion factor shall be less than 1% when the output level is +7.5dBu at PHONES (L/R).
In measuring the ST L OUT, the ST R OUT and the GROUP1/2 OUT, set the PAN or BAL Control to L or R fully respectively. 2-11.PEAK LED light-up level
Each LED shall light-up within the range specified in the Table 2-11-1 when a signal is fed to the MIC input.
INPUT PEAK LED
MIC -43 +/- 2
Table 2-11-1 [dBu ]
2-10. Crosstalk
Setting the fader to the nominal position and each input channel ON switch to ON, and turning the PAN control shall be -50dBu
or (PAN/BAL or BAL control in the case of ST CH INPUT) counterclockwise fully, the level of the leakage to ST R OUT less
when the output level of ST OUT is +20dBu.
Also turning the PAN (PAN/BAL, BAL) control clockwise fully, the level of the leakage to ST L OUT shall be -50dBu or less
when the output level of ST R OUT is +20dBu. 
						

							43 MG12/4
MG16/4
2-17 PHANTOM
Connect a 10kΩ load resistance between the pin 1 and 2 of the MIC and short-circuit between the pin 2 and 3.
Turn on the PHANTOM switch(LED shall light) and the voltage between pin 1 and 2 shall be within +35 +/- 3V. Table 2-16-1 [dBu ]
Fader/VR STEREO OUT GROUP OUT AUX OUT C-R OUT
MAX -78.0 -80.0 -75.0 -72.0
MIN -100.0 -100.0 -100.0 -87.0
2-15. Equivalent Input Noise
In the state 2-2, connect between the CH INPUT MIC terminals (2pin-Hot and 3pin-Cold) with 150 ohms, the noise level obtained
at ST L OUT shall be less than -43.5dBu.
If it is over than -43.5dBu, calculate the input converted noise level (=noise level -channel gain) and it shall be less than
-127.5dBu.
Connect between the ST INPUT MIC terminal
s (2pin-Hot and 3pin-Cold) with 150 ohms, the noise level obtained at ST L OUT
shall be less than -39.5dBu.
If it is over than -39.5dBu, calculate the input converted noise level (=noise level -channel gain) and it shall be less than
-123.5dBu.
(Noise is measured with a 12.7kHz -6dB/octave low pass filter.)
2-16. Residual Noise
In the state 2-2, set the Fader and Level Control of all input CH to MIN and set the all Assign switch to OFF.
Then, the noise level shall be less than the level specified in the Table 2-16-1.
* In measuring the C-R OUT and the PHONES, set the ST Fader to MIN.
(Noise is measured with a 12.7kHz -6dB/octave low pass filter.) 
						

							44 MG12/4
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							 WARNINGComponents having special characteristics are marked       and must be replaced with parts having
specification equal to those originally installed.
Notes : DESTINATION ABBREVIATIONS
The numbers “QTY” show quantities for each unit.
The parts with “--” in “PART NO.” are not available as spare parts.
This mark “ } ” in the REMARKS column means these parts are interchangeable.
The second letter of the shaded (
) part number is O, not zero.
The second letter of the shaded (
) part number is I, not one.
M : South African model
O : Chinese model
Q : South-east Asia model
T : Taiwan model
U : U.S.A. model
V : General export model (110V)
W: General export model (220V)
N,X: General export model
Y : Export model A : Australian model
B : British model
C : Canadian model
D : German model
E : European model
F : French model
H : North European model
I : Indonesian model
J : Japanese model
K : Korean model
 CONTENTS
OVERALL ASSEMBLY ............................................... 2
ELECTRICAL PARTS ...................................... 4 – 25
PARTS LIST
MIXING CONSOLE
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							MG12/4
2
210
450
450430
460
280270260250
250
360
310
430
440
430460460
460460430
430
15
30
30
30
15
120
440
480
140
500500
510
510130
510
420
150
400
10
180
20
70
40a
50
60
40
350520
520
320
320
320
320
250
220230
100320110
310
170
450
40b
JACK 1/2 JACK 2/2
430
430
300

 Rear view
Reflector meter