Service manual

42
EMX68S / EMX88S
3.1.8 Stability Check
(1) Connect 10pF~0.47µF capacitor in parallel to the 4Ω load resistance and apply rectangule signal of 10kHz/-26dBs.
Then, confirm that overshoot and ringing are as follows.
Overshoot: Vp/Vo
<
=
1.8
Ringing: within 5 waves
(2) Connect 10µH~0.47H inductor in series to the 4Ω load resistance and apply rectangule signal of 10kHz/-26dBs.
Then, confirm that overshoot and ringing meet the same condition as (1).
(3) Remove the 4Ω load resistance and connect only 10pF~0.47µF capacitor as load, and apply rectangule signal of 10kHz/-
26dBs.
Then confirm that the system does not oscillate.
Besides, confirm that overshoot and ringing are as follows.
Overshoot: Vp/Vo
<
=
2.5
Ringing: within 7 waves
3.1.9 Protection Circuit Check
(1) Apply 10Hz signal until output level is saturated, and confirm that the protection circuit works and the relay does not open.
(2) Apply 1Hz, Vp-p = 6V(8.7dBs) signal, and confirm that the protection circuit starts to work in 2 seconds to cut off the signal.
(3) Stop applying the input signal, and confirm that the system automatically resumes in 5 seconds.
3.1.10 PC LIMITER Circuit and LIMITER Circuit Check
(1) Connect 1Ω(±5%, 100W) load and apply -20dBs signal into input terminal.
(2) Confirm that the protection circuit starts to work and indicator LED lights up.
(3) Stop applying the input signal, and confirm that the system automatically resumes in 5 seconds.
3.1.11 LIMITER Indicator Check
Apply 1kHz/-10.8dBs signal, and confirm that LIMITER indicator lights up.
3.1.12 Efficiency Check
Apply 1kHz/-24dB signal into input terminal, and confirm that the primary power is 250±50W.
If the primary power does not meet the rated value, adjust the input level until the output level of SPEAKERS becomes
14.1V(25.2dBs).
3.2 For the case that the POWER AMP switch is 'BRIDGE'
3.2.1 Preparation
• Connect load resistance of 8Ω (more than 800W) to SPEAKERS terminal.
• Set each control as follows.
POWER AMP switch: BRIDGE
LEVEL control of CH1-4, 6 (EMX68S): MIN
LEVEL control of CH1-6, 8 (EMX88S): MIN
Except the above, same as the setting of 2.1.
Note: Use following channels for input and output terminals.
Input: CH 5 LINE L (EMX68S) / CH 7 LINE L (EMX88S)
Output: (SPEAKERS) L+R BRIDGE
3.2.2 Gain Check
Apply -26dB signal into input terminal, and confirm that the output level of 23±2 dBs can be gained.
3.2.3 Frequency Response Check
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.
4. Miscellaneous
4.1 Power Supply Voltage Variation
Change the voltage of power supply in the range of ±10%, and confirm that the system works normally.