Yamaha EMX3000 Service Manual page 31

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B. INSPECTION OF POWER AMPLIFIER
INSPECTION AT ST1L-ST1R
1 PREPARATIONS
• Input terminal: ST SUB IN 1 L/MONO
• POWER AMP Switch : ST1L-ST1R
• POWER AMP (L/BRIDGE, R) level control:MAX
• Output terminal: SPEAKER L (1), SPEAKER R (1)
• Load resistance: 40 ohm (300W or more)
Unless otherwise specified, the load resistance of the speaker should be connected only when checking the power amplifier.
• Set all the Fader/Level controls of channels1 to 10, SUB IN 2 and TAPE IN to the minimum position.
• Other than the above, use the same setting as described under PREPARATIONS for inspection.
2 Muting function at power ON
• Check that the muting function is cancelled and the relay turns on at 2.5 +/- 1 seconds after the POWER switch is turned on.
3 Fan
• Short-circuit the 2 jumper wires within the frame (between C141 and Q139) marked FAN-C in the PWR circuit board and
check that the fan runs at a low speed.
4 DC voltage at output terminal
• Ground the input terminal and check that the DC voltage at the output terminal is 0 +/- 100mV.
5 GAIN
• Input a -9.0 dBs signal to the input terminal and check that the output level of measured gain is as specified in Table 5-1 when
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L 13942296513
the POWER AMP switch setting is changed.
[Table 5-1] Gain
POWER AMP switch
SPEAKER L (1,2)
SPEAKER R (1,2)
6 FREQUENCY RESPONSE
• Input 20Hz, 1kHz, 20kHz/-9.0dBs sine wave signals to the input signal and check that the frequency response at 20Hz and
20kHz is within the range of +1.0/-3.0dB with 1kHz used as a reference.
7 TOTAL HARMONIC DISTORTION
• Input a 1kHz signal to the input terminal and check that the total harmonic distortion is 0.5% or less when 300W + 300W/4
ohm (33.0dBs) output is obtained.
• Also, input 20Hz, 2kHz and 20kHz signals to the input terminal and check that the total harmonic distortion is 0.5% or less
when 150W + 150W/4 ohm (30.0dBs) signal is obtained at the output terminal.
8 RESIDUAL NOISE
• Set the POWER AMP L/BRIDGE, POWER AMP R level controls to the minimum position and check that the noise level at the
output terminal is -62dBs. Use care so that the measurement is not affected by the induction noise. (Use the DIN audio filter.)
9 STABILITY
• With 10kHz • -3.2dBs rectangular signal input, connect 10pF to 0.47 µ F capacitance in p parallel with 4 ohm load resistance
or 10 µ H to 0.47H inductance and check that the following items are satisfied.
Overshoot:
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Ringing:
.
• Disconnect 4 ohm load resistance to make the load consisting of 10pF to 0.47 µ F capacitance only, check that ringing is
within 7 waves at Vp/Vo
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ST1L-ST1R MONI 1-MONO
+20.0 +/- 2.0 +23.0 +/- 2.0
+20.0 +/- 2.0 +23.0 +/- 2.0
Vp/Vo 1.8
Within 5 waves
Vp
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2.5 and no oscillation or the like occurs.
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2 9
8
Q Q
3 6 7 1 3 1 5
[Unit: dBs]
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9 4 2 8
0 5 8 2 9 9 4 2 8
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EMX3000
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