Yamaha XS250 Service Manual page 15

13. Signal Indicator Test
When a sine wave of 1 kHz, -23 dBu is applied to the input, SIGNAL indicator should light up.
B BRIDGE Operation
Before performing any following adjustments, set the unit as follows:
1. Set the ATTENUATIONS at MAX.
2. Input terminal:
3. MODE switch:
4. Output terminal:
5. Connection for measuring: Measure the output at the point as shown below.
SPEAKERS
CHANNEL A
+
CHANNEL B
-
Adjustment Specifications
1. Gain Test
Check that the OUTPUT should be +22.1 +/-1.0 dBu, when asine wave of 1 kHz at -10 dBu is applied to the INPUT.
2. Frequency Response Test
When a sine wave of 20 Hz, 1 kHz or 20 kHz at -10 dBu is applied to the INPUT, check that the output is 0 +/-0.5 dB at 20 Hz and -0.5
+/-0.5 dB at 20kHz taking the 1 kHz as a reference.
3. Harmonic Distortion Test
When a high quality sine wave is applied at 20 Hz, 1 kHz or 20 kHz, the harmonic distortion should be as follows:
Power output level
(4 ohm)
XS350 33.7 dBu
</= 0.1 %
XS250 32.2 dBu
*This test should have been finished within 30 minutes.
4. Noise Test
9-1 Set the input attenuator to "0".
9-2 Short the input with a 600 ohm load.
9-3 Measure at the output, noise level should be less than -60 dBm. (LR = 8 ohm)
9-4 Set the input attenuator to "∞", noise level should be less than -60 dBu
*Be careful that it is not affected by noise induced during this inspection.
C Settings after the test
The attenuator should set to "∞".
The MODE switch should set to STEREO.
D Others
0 dBu = 0.775 V
When measuring noise level,use a DIN audio filter.
Cannon connector pin 2 is HOT, pins 1 and 3 GROUND.
BRIDGE
(A ch+, B ch+) RL = 4 + 4 ohm/more than 500 W
MEASURING
INSTRUMENT
INPUT
4 Ω
GND
4 Ω
THD
20 Hz 1 kHz 20 kHz
</= 0.1 % </= 0.1 %
XS250/350
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