QSC CX Series, Service Manual

Page: 17 / 90

CX Series
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FINAL CHECK
This completes the amplifier test procedure for this model. Inspect the amplifier for mechanical
defects. Inspect the solder connections. Reassemble the amplifier and verify the amplifier’s
operation before returning the product to service.
CX
1
2 / CX
1
2T Test Procedure
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S E T - U P
1.
2.
3.
4.
5.
6.
7.
Connect a test load to the output terminals of the amplifier.
Make sure the Stereo / Bridge switch is set to the Stereo position.
Connect a distortion analyzer with a resolution of 0.05%, 20-20kHz (or better) to the output
terminals of the amplifier. Enable the 8
0
kHz low pass filter.
Connect a dualchannel oscilloscope to the following test points:
Ch
1
-
a 1 OX (vertical sensitivity
-
2V/cm) scope probe to the channel speaker output.
Ch2
-
a 1 X scope probe (vertical sensitivity - 0.
1
V/cm) to the distortion analyzer
output.
Set amp gain pots fully clockwise and turn on power switch.
Connect the output of the signal generator to the input terminals of the amplifier and select
an output of 1
.00
VRMS, 1 KHz sine wave.
Plug the amplifier in to a variac and set up an AC line current monitor.
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POWER UP & MUTE DELAY TEST
1.
Slowly raise the variac voltage and watch for excessive current draw (Line current greater
than
0.5A
a.c. at 60 Volts).
This is slightly less for
24
0
V
Pause at 9
0
VAC
(
200
VAC
European)
for three seconds until the mute / protect circuit disengages, Continue to 12
0
VAC
(240V European).
2.
Turn the power switch off and on a few times to verify the 1 - 3 second power-up muting
delay. Check both channels.
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CHANNEL OUTPUT
1. Look for amplified signal on the scope for channel
1
Switch the input signal and scope to
channel 2 and repeat output test. Check for noisy / contaminated gain pots by looking for
general instability on the distortion waveform while adjusting the gain control levels.
2. Select an 8 ohm load and confirm with the gain controls that this amplifier is producing a
minimum of 430 watts at 1 kHz just beyond the point of clipping (1
.0%
THD+N). Check both
channels.
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BRIDGE MODE
1. Turn the power switch off and the gain controls down.
2, Move the bridge switch on the amp from the Stereo to Bridge position.
3. Set an 8 ohm load to both red output binding posts (CH
1
positive and CH2 negative). Remove
the input connector from channel 2.
4. Apply a 1VRMS
,
1 kHz sinewave input to channel 1 of the amplifier. Check for 1200 watts at
0.1% THD+N and verify that the output does not collapse. The position of CH2’s gain control
does not affect the output level.
5, Turn power off and place the amplifier under test back into the Stereo mode with output loads
connected to each channel. Reinsert CH2 input plug and turn both gain controls fully up.
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