ALTO MODEL: L12 - L16 - L20 – Professional Equalizer – Circuit Diagram - Testing

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Functions test
a. Input the proper AC power supply, turn on the main power, POWER LED will be illuminated (green). Then switch on PHANTOM power, PHANTOM LED will be illuminated (red), use a voltmeter to test the first pin and second pin of each MIC (MIC 1, MIC 2), the volt of phantom power should be 46V(±2V). then power off the switch.(Note: please turn off the switch when you are doing the steps of test procedure as follows)
b. Set all TRIM, LEVEL, EQ, AUX knobs to the position of 0, set PAN to the position of LEFT. All buttons to the position of OFF.
c. Input the signal from balanced sockets (MIC 1 & MIC 2), input the signal from  unbalanced sockets (LINE IN 3/4&LINE5/6)
d. Input the signal to the unbalanced AUX RENTURN sockets separately, test the balanced output (LEFT & RIGHT) of MAIN MIX OUTPUT, which should be 5dBu (±1dB) THD + N<0.003%.
e. Insert the RCA plug to L& R of TAPE IN separately:
First, press 2TK TO MIX button, test the unbalanced outputs (LEFT&RIGHT) of MAIN MIX OUTPUT, CONTROL ROOM and PHONE (need stereo plug for testing) separately, which should be 0dBu(±1dB) THD + N<0.006%.the output of TAPE OUT is 0dBu(±1dB)
Then release 2TK TO MIX button (OFF), no input from CONTROL ROOM, when press 2TK TO CONTROL ROOM, test the output, which is 0dBu (±2dB) THD + N<0.002%.

f. Input +15dBu 1kHz sine wave (load out 600Ω, BNC-Unbalanced) through LINE 1, when turn MAIN MIX LEVEL counter-clockwise to the minimize, all LEVEL LEDs will turned off, when turn MAIN MIX LEVEL pot clockwise to the
maximize, the LEVEL LEDs will be illuminated in sequence. test that whether the relating LED is illuminated when the level of output signal reaches the exactly value as LED shows . If so, test the maximize output level (before clipping) is
20dBu(±1dB) THD + N<0.1%.)
Adjust TRIM knob of CH 1 clockwise, PEAK LED will be illuminated (red). And test all PEAK LEDs from CH 1 to CH6
frequency response test
When Test the inputs of LINE 1, LINE 2, LINE 3, LINE 4, LINE 5, LINE 6 separately as follows, the frequency response curve of MAIN MIX OUTPUT (LEFT & RIGHT) (the preset of all knobs are the same as function test step 2.b)
a. Open S8RESP1.atl test procedure, press and release the LOW CUT switch, test the frequency response curve of LINE 1, LINE 2 LINE 3, LINE 4

b. Turn EQ HI &LOW knob to the MAX and the MIN (EQ MID at the middle), test the frequency response.

c. Turn EQ MID to the MAX and the MIN (EQ HI &LOW at the middle), test the frequency response.

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Remarks: the frequency response test of normal instruments

a. Turn EQ LOW knob of the relating channel clockwise to the max (+15), the output is +15dBu(± 2dB), then turn EQ LOW knob of the relating channel counter-clockwise to the min. (-15), the output is –15dBu(± 2dB)

b. Input the signal at 2.5kHz, Turn EQ MID knob of the relating channel clockwise to the max (+12), the output is +12dBu(± 2dB), then turn EQ MID knob of the relating channel counter-clockwise to the min. (-12), the output is –

12dBu(± 2dB)

c. Input the signal at 15kHz, Turn EQ HIGN knob of the relating channel clockwise to the max (+15), the output is +15dBu(± 3dB), then turn EQ HIGH knob of the relating channel counter-clockwise to the min. (-15), the output is –15dBu(± 3dB)

DSP

a. Input the signal from MIC1, output the signal from MAIN MIX OUTPUT, turn AUX RTN2(DFX)clockwise to the MAX, turn PRESETS and VARATIONS knobs, the signal will be processed by DSP, if the level of the signal is over-high, PEAK LED will be illuminated to red, press DFX MUTE button, Bypass the signal, press the footswitch, which is connected to DFX FOOSWITCH, the signal will get out of BYPASS.

b. Input the signal from MIC 1 to MIC 4, output the signal from AUX SEND S1, turn AUX 2 /DFX TO AUX 1 counter-clockwise to the MAX., turn PRESET and VARATIONS knobs, the signal will be processed by DSP. (do not need to test L6 with this step)

Sampling test

Connecting L 6 to a power amplifier and speakers, listening to the sound, no noise is OK.

Company preset: turn all volume knobs to the MIN. other control knobs to the middle, all switches to the position of OFF.