QSC CX Series, Руководство по обслуживанию

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channels the same for a change in current limiting. Both wipers need to adjust
evenly to achieve a balanced setting.
e. Once the correct AC current draw is set, remove the short on the output. When this
is done, the output power should spring back into the 4 ohm load. If it does not,
the current limits are set too low.
f. Once the output recovers into the 4 ohm load, verify that both polarities of the
output sinewave are clipping at the same time. If one polarity clips before the other,
adjust the current limit for that polarity
(1
+ or I
- )
until both polarities clip at the
same time.
g
.
After the short circuit current is set and even clipping is achieved, reapply the short
to the output to reconfirm AC line current. If the current draw is not within the
range specified, again balance the current limit trimpots until even clipping and the
correct AC current draw is met.
h. Remove the input signal from CH
1
and calibrate CH2. It is important to calibrate
only one channel at a time.
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FREQUENCY RESPONSE
1. Set load to 8 ohms and scale the input generator to gain 1 watt of power from the amplifier on
each channel. Gain controls on the amplifier should be fully up.
2. Check frequency response from 2
00
Hz to 20kHz (+/- 0.2dB) by sweeping random frequencies
between these extremes. This is done by verifying the same voltage amplitude at each of
the frequencies selected (within 2
00
Hz to 20kHz). The frequency extremes for the CX6Tdirect
outputs is between 45Hz and 16kHz (-3dB
@
45Hz, -0.2dB
@
20 kHz). Check both channels.
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POWER vs. DISTORTION TEST
1. Check to ensure that both channels will produce rated power at 2
00
Hz, 2KHz, and 2
0
kHz. into
an 8 ohm load. For the CX6T under test, check power levels between 2
00
Hz, 2kHz, and
20kHz (-3dB @ 45Hz, -0.2dB
@
16 kHz).
2, While verifying rated power, check that at all frequencies the distortion measurement is less
than or equal to 0.1%. To obtain this measurement, check to ensure that the 80kHz low pass
filter is engaged on the analyzer. Check distributed lines (7
0
V, 1
00
V) with 40 ohm, 20 ohm,
or 10 ohm loads to ensure that both channels will produce rated power at 45Hz, 2kHz, and
16kHz.
l
THERMAL TEST
1.
Set input frequency to 1 KHz and short both channels while they are producing power into a
load.
2. AC line current draw should be about 7.0 - 8.0 amps for both channels. As the amplifier gets
hot, there will be some current drift upwards. This is not a problem as long as the case
temperature on the output transistors does not exceed 105 degrees C.
3. Verify that the PTC circuit causes thermal shutdown after an extended period of time.
4. While the amplifier is progressing towards thermal shutdown, look for the fan to cut into high
speed.
5. When thermal shutdown occurs on both channels, verify AC idle current of less than 2.5
amperes.
6. Remove short to verify thermal protect
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