Inspections - Yamaha XS250 Service Manual

INSPECTIONS

A STEREO and PARALLEL Operation
Before performing any following adjustments, set the unit as follows:
1. Set the ATTENUATIONS at the MAX.
2. Input terminal: Cannon connector pin 2 is HOT, pins 1 and 3 GROUND.
3. MODE switch: STEREO
4. Output terminal: RL = 4 ohm/more than 500 W
5. Others: Both Channel operation is required, if no particular indication. Moreover, turn off the filter switch,
if no particular indication.
Adjustment Specifications
1. Fan Test
When turning on the power switch, confirm that both fans of right and left sides regulate at low speed.
2. Muting Test
After applying power to the unit, the PROTECTION indicator should remain ON 2.5 +/-1 seconds to indicate that the protection circuitry
is operating and the indicator should go out. NO signal is output while this indicator lit.
3. Idle Current Test
Connect the input terminal to the GROUND and adjust the VR201 (A channel) and VR301 (B channel) that the DC voltage Vb between the
pin 1 and pin 2of the CN202 (A channel) and the CN302 (B channel) should be 1.0 +/-0.2 mV. And After finishing all tests, adjust the Vb
again to 1.0 +/-0.2 mV.
4. Input Terminal DC offset
Connect the input terminal to the GROUND and check that the DC voltage Vdc of the output terminal should be 0 +/-75 mV.
5. Gain Test
Check that the OUTPUT should be +22.1 +/-0.5 dBu, when a sine wave of 1 kHz at -10 dBu is applied to the INPUT. This test should be
performed on PARALLEL operation.
6. Frequency Response Test
Filter switch OFF:
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 20 kHz taking the 1 kHz as a reference.
Filter switch SUB WOOFER:
<MIN>
When a sine wave of 25 Hz, -10 dBu is applied to the INPUT, check that the output is -3.5 +/-1.0 dB taking the 1 kHz as a reference at the
filter switch OFF.
<MAX>
When a sine wave of 150 Hz, -10 dBu is applied to the INPUT, check that the output is -3.5 +/-1.0 dB taking the 1 kHz as a reference at the
filter switch OFF.
Filter switch LOW CUT:
<MIN>
When a sine wave of 25 Hz, -10 dBu is applied to the INPUT, check that the output is -4.5 +/-1.0 dB taking the 1 kHz as a reference at the
filter switch OFF.
<MAX>
When a sine wave of 150 Hz, -10 dBu is applied to the INPUT, check that the output is -3.5 +/-1.0 dB taking the 1 kHz as a reference at the
filter switch OFF.
XS250/350
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