Yamaha EMX 620 Service Manual page 19

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3. Power Amplifier Part
3-1 Setting Conditions
Setting conditions are as follows unless otherwise specified.
Input Terminal:
Measuring Output Terminal:
Output Load:
Connect the resistor when inspecting the power amplifier section.
INPUT CH1-CH6
MONITOR level control:
EFFECT level control:
LEVEL level control:
Note: Other control settings are the same as the mixer part in section 2-3.
3-2 Power ON Muting
The muting relay should be released 2.5 +/- 1 seconds after the power switch is turned on.
3-3 Speaker Terminal DC Voltage
When input terminals are grounded, confirm that each output terminal voltage is 0 +/- 100 mV.
3-4 Gain
When applying a 1 kHz -26.0 dBs sine wave to an INPUT terminal, confirm that the SPEAKER A and MONITOR terminal output
level is +20 +/- 2.0 dBs.
The SPEAKER B output terminal should be measured.
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3-5 Frequency Response
L 13942296513
Apply a 20 Hz, 1 kHz and 20 kHz = 26 dB sine wave signal separately to the input; the output level should be between -3 and +1dB
at 20 Hz and 20 kHz, when 1 kHz is set as the reference.
3-6 Harmonic Distortion
Apply a 1kHz sine wave signal to the input; the three output level should be 200 W/4 ohms (31.2 dBs/ch); the distortion ratio should
be less then 0.5 %.
Apply a sine wave signal of 20Hz, 1kHz and 20 kHz separately to the input; the three output level should be 100 w/4 ohms (28.2 dBs/
ch); the distortion ratio should be less than 0.5 %.
Do this inspection within 30 seconds.
3-7 Residual Noise
Set the MASTER level controls (MONITOR and MAIN) at minimum; the residual noise should be less than -68 dBs.
Note: Apply a DIN-LOW PASS filter.
3-8 Stability
Apply a 10 kHz -26 dBs rectangular signal to the input and connect a capacitor (10 pF to 0.47
or connect an inductor (10
Overshoot:
Ringing:
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Next, only connect a capacitor (10 pF to 0.47
Overshoot:
Ringing: It should end within 7 waves; there is no oscillation.
.
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Minimum
Minimum
Minimum
µ
H to 0.47 H) serial to the 4 ohm load resistor. Confirm that the output signal is as illustrated below.
Vp / Vo <= 1.8
5waves and less than 5 waves
µ
F) to the SPEAKERS terminal as a load, and confirm that the output is as follows:
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Vp / Vo <= 2.5
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2 9
8
INPUT CH 5 LINE 1
SPEAKERS A
4 ohm (more than 200 W)
Q Q
3 6 7 1 3 1 5
co
.
9 4 2 8
0 5 8 2 9 9 4 2 8
µ
F) parallel to the 4 ohm load resistor,
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EMX620
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