Service manual

EMX68S / EMX88S

3. Power Amplifier Check

3.1 For the case that the POWER AMP switch is 'MAIN(L+R)-MON' or 'MAIN L-MAIN R'

3.1.1 Preparation

• INPUT terminal: CH 7 LINE L(EMX88S) / CH 5 LINE L(EMX68S)

• POWER AMP switch: MAIN L-MAIN R

• OUTPUT terminal: SPEAKERS A1, SPEAKERS B1

• Load Resistance: 4Ω (more than 400W)

Except otherwise indicated, the load resistance should be connected only for the power amplifier check.

• Set the LEVEL control of CH1-4, 6 (EMX68S) and CH1-6, 8 (EMX88S) to minimum.

• Except the above, same as the setting of 2.1.

3.1.2 Power ON Mute Check

Turn on the power and confirm that the mute system is released and the relay is switched on after 2.5±1 seconds.

3.1.3 Output Terminal D.C. Voltage Check

Ground input terminal and confirm that the D.C. voltage of output terminal is 0±100mV.

3.1.4 Gain Check

(1) Apply -26dBs signal into the input terminal and confirm that the output level of SPEAKERS A1, B2 is 20.0±2.0dBs.

(2) Set the POWER AMP switch to ’MAIN(L+R)-MON ’, perform the same mesurement, and confirm that the output levels are as

follows.

SPEAKERS A1, A2: 23.0±2.0dBs

SPEAKERS B1, B2: 26.0±2.0dBs

3.1.5 Frequency Response Check

• YAMAHA SPEAKERS PROCESSING Switch OFF

Apply -26dBs signal into input terminal, and confirm that the output level for 20Hz, 20kHz signal are within +1, -3dB from the

level for 1kHz signal.

• YAMAHA SPEAKERS PROCESSING Switch ON

Apply 70Hz / -26dB signal into input terminal, and confirm that the output level is within 6.5±2dB from the level for 1kHz input

with YAMAHA SPEAKERS PROCESSING switch OFF.

Besides, confirm that the LED lights up when YAMAHA SPEAKERS PROCESSING switch is ON and that LED goes out when

the switch is OFF.

3.1.6 Harmonic Distortion Rate Check

Note: This mesurement should be finished in 30 seconds.

• Apply 1kHz signal into input terminal, and confirm that output level of 400W/4Ω (34.3dBs) can be gained with harmonic

distortion rate less than 0.5%.

• Apply 20Hz, 1kHz and 20kHz signal into input terminal, and confirm that harmonic distortion rate is less than 0.5% as for 20Hz

and 1kHz, less than 0.7% as for 20kHz when output level of 200W/4Ω (31.2dBs) can be gained.

3.1.7 Remaining Noise Check

Set the MASTER control of MAIN and MONITOR to minimum, and confirm that the noise level of output terminal is less than

-65dB.

Note: Take care not to be affected by inductive noise.

This mesurement should be performed by using DIN AUDIO FILTER.