Yamaha MX-630 - Troubleshooting; Common Symptoms and Remedies

If the unit fails to operate normally, check the following points to determine whether the problem can be corrected by the simple measures suggested. If it cannot, or if the problem is not listed in
the SYMPTOM column, disconnect the unit's power cord and contact your dealer or service center for assistance.
The power is not switched ON when the POWER
switch is pressed.
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The power cord plug is not connected securely to the wall
power outlet.
No sound is heard.
No sund is heard from the left and/or right speaker
systems.
The acoustic “image” is unstable, characterized by
unnatural sound and insufficient low-range tonal
quality.
Hum noise is heard from the speakers.
The SPEAKERS switches are released outward to the “OFF”
position. :
The speaker level controls are set all the way to the " OO "
position.
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Connect it securely.
Press them inward to the “ON” position.
Turn them clockwise.
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The connection cords are not connected securely to the INPUT
jacks.
The speaker systems are not properly connected to this unit.
The speaker systems are not properly connected to this unit.
One of the speaker level controls is set to the fuily
counterclockwise position.
The positive (+) and negative (-) polarities (of this unit and
the speaker systems) are not matched.
Connect them securely.
Connect them correctly.
Connect them correctly.
Turn that speaker level control clockwise.
Reconnect the speaker systems to this unit so that the
polarities are aligned.
The connection cords are not connected securely to the INPUT
jacks.
Connect them securely.