QSC CX Series User manual

CX Series
CX4
CX12

CX Series
CX4T
CX1 2T

CX SERIES AMPLIFIER
SERVICE MANUAL
CX4 - CX4T
CX6 - CX6T
CX12 - CX12T
QSC Technical Services
Wats: 1-800-772-2834
Local: 1-714-957-7150
Fax: [phone]
QSC Online!
Online Computer Information System
1-800-856-6003
I-71 4-668-7567
QSC Audio Products, Inc.
1675 MacArthur Blvd.
Costa Mesa, CA 92626
http://www.qscaudio.com

CX Series Chassis Drawings
CX4 Chassis Assembly....................................................................
42
CX4T Chassis Assembly..................................................................
45
CX6 & CX12 Chassis Assemblyy........................................................ 48
CX6T & CX12T Chassis Assemblyy .................................................... 48
CX 4 / 4T Display Board Schematic.................................................. 39
CX 6T & 12T Display Board Schematic.............................................
39
CX4 /4T Series Main Amplifier Board.................................................
40
CX6 /6T Series Main Amplifier Board................................................
41
CX12 /12T Series Main Amplifier Board..............................................
42
CX Series Wiring Diagrams
CX4 Wiring Diagram (120v))
..............................................................
56
CX4 Wiring Diagram (100v))
..............................................................
57
CX4 Wiring Diagram (230v))
..............................................................
58
CX4T Wiring Diagram (120v))
............................................................
59
CX4T Wiring Diagram (100v))
............................................................
60
CX4T Wiring Diagram (230v))
............................................................
61
CX6 Wiring Diagram (120v))
..............................................................
62
CX6 Wiring Diagram (100v))
..............................................................
63
CX6 Wiring Diagram (230v)
..............................................................
64
CX6T Wiring Diagram (120v))
.............................................................
65
CX6T Wiring Diagram (100v)
.............................................................
66
CX6T Wiring Diagram (230v)
............................................................. 67
CX12 Wiring Diagram (120v)
............................................................. 68
CX12Wiring Diagram (100v)) ..............................................................
69
CX12 Wiring Diagram (230v))
.............................................................
70
CX12T Wiring Diagram (120v)
...........................................................
71
CX12T Wiring Diagram (100v))
...........................................................
72
CX12T Wiring Diagram (230v))
...........................................................
73

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CX Series
*-“-” *“arT‘
CX Series Product Specifications
CX6
cx4
CX12
Output Power (per channel):
Continuous Average Output Power both channels driven:
8 ohms, 20Hz - 20kHz, 0.1% THD 150 watts
4 ohms, 20Hz - 20kHz, 0.1% THD 225 watts
2 ohms, 1kHz, 1% THD*
350 watts
Continuous Average Output Power bridged mono
oDeration:
8 ohms, 20Hz - 20kHz, 0.1% THD
4 ohms, 1 kHz, 1% THD*
Voltage Gain
(@ direct outputs):
Sensitivity (for rated power
@ 8 ohms):
Distortion:
SMPTE-IM
Frequency Response:
Damping Factor
(@ direct outputs):
Noise:
Input Impedance
Dimensions
Faceplate
Width
Faceplate Height
Chassis Depth
Weight
Shipping, Lbs/kg
Net, Lbs/kg
450 watts
700 watts
35x(31
dB)
0.96 V rms
200 watts 400watts
300 watts 650 watts
4500 watts 650 watts
600 watts
400 watts
40x (32 dB)
1 .02 Vrms
1200 watts
1800 watts
56.5 (35
dB)
1 .00 Vrms
Less than 0.05%
20Hz to 20kHz, +/-0.2dB
200
1 00dB below rated output (20 Hz to 20 kHz)
10k unbalanced, 20k balanced
Standard 19” Rack Mounting
3.5” (13.3 cm) 5.25” (13.3 cm)
17.9” (45.5 cm) 17.9” (45.5 cm)
36/16.4 53/24
30/13.6 44/20
5.25” (13.3 cm)
17.9” (45.5 cm)
58/26.3
50122.7

CX Series Product Specifications CX Series
CX4 T
CX12T
CX4T
Output Power (per channel):
Direct Output, watts per channel, both channels driven:
8 ohms, 45H.z
- 20kHz, 0.1% THD 150 watts
4 ohms, 45Hz - 20kHz, 0.1% THD 225 watts
2 ohms, 1 kHz, 1% THD*
350 watts
Isolated outputs, watts per channel, both channels driven:
70V or
100V, 45Hz-16kHz, 0.25% THD
70V or 100V,
1 kHz, 0.1% THD 175 watts
25V, 45Hz-16kHz, 0.25% THD
25V, 1 kHz, 0.1% THD 150 watts
Direct Outputs, bridged mono:
8 ohms, 45 Hz-20kHz, 0.1% THD 450 watts
4 ohms, 1kHz, 1% THD 700 watts
CX6T
200 watts
300 watts
450 watts
250 watts
250 watts
600 watts
900 watts
CX12T
400 watts
600 watts
900 watts
500 watts
500 watts
1200 watts
1800 watts
Voltage Gain
(dB):
Sensitivity (for rated power @ 8 ohms)
Distortion:
SMPTE-IM
Frequency Response:
Damping Factor:
Noise:
Input Impedance
Dimensions
Faceplate Width
Faceplate Height
Chassis Depth
Weight
Shipping,
Lbs/kg
Net, Lbs/kg
35x(31 dB)
40x (32 dB)
0.98 V rms 1.02 Vrms
56.5x (35 dB)
1 .00Vrms
Less than 0.05%
-3dB @
45Hz*, -0.2dB @20kHz ;direct outputs
45Hz* -16kHz, + 0 , 3dB ;isolated outputs
*Low Frequency is limited by 18 dB/octave 45 Hz high pass filter
200 (@ direct outputs)
1
00dB below rated output (20 Hz to 20 kHz)
10k ohms unbalanced and 20k balanced
Standard 19” Rack Mounting
3.5” (13.3 cm)
5.25” (13.3 cm)
17.9” (45.5 cm)
17.9” (45.5 cm)
46/21 62/28
40/18.2 55/25
5.25” (13.3 cm)
17.9” (45.5 cm)
75/34
67/30.4

CX Series
I n t r o d uc t i on
This manual is prepared to assist service personnel with the repair and calibration of the
CX Series power amplifiers The procedures described in this manual require advanced
technical experience and sophisticated audio test equipment.
A A
CAUTION: To reduce the risk of electric shock, do not remove the cover. No user-
serviceable parts inside. Refer servicing to qualified service personnel.
WARNING: To prevent fire or electric shock, do not expose this equipment to rain
or moisture.
Documentation
This manual contains schematics, printed circuit board (PCB) drawings, parts lists, and
mechanical assembly drawings. This information should be used in conjunction with the test and
troubleshooting guide.
The electrical and electronic components are identified by circuit identification numbers on the
schematics and the parts list, The test & troubleshooting sections refer to designations shown in
the schematics.
EquivalentParts
Although many of the electronic components used in this product may be available from
electronic suppliers, some components are specially tested and approved by QSC. A product
repaired with non-QSC supplied components may not meet factory specifications.
Repairs
performed using non-QSC parts may void the product warranty, When in doubt, you may contact
QSC Technical Services for assistance.
Parts orders to QSC should include the product model number, the part description, and the QSC
part number (from the parts list in this manual). Parts will be shipped via UPS, F.O.B. Costa Mesa,
California, Shipping, handling and COD charges may be added to the cost of the parts.
Factory Repair
It may become necessary to return a product to the factory for repair. Call QSC Technical
Services for return instructions. You must obtain a Return Authorization number from QSC before
returning a product to the factory. QSC Technical Services may be reached at [phone].
3

CX Series
Test Equipment
For testing, as outlined in this manual, the following equipment will be needed.
REQUIRED TEST EQUIPMENT
SUGGESTED TEST EQUIPMENT
- Distortion Analyzer capable of 0.05% THD+N
* Audio Precision System One
- High Power Load Bank (8, 4, & 2 ohms) for CX
- Thermocouple probe
- High Power Load Bank (40,20, & 10 ohms) for CX T
- Function Generator
- 20MHz Oscilloscope
- Digital Multimeter
- Variac (0-l 40 VAC, 20-30A)
Audio Precision test and procedures files are made available, free of charge, from QSC Technical
Services by either sending a self addressed stamped envelope and a 3 1/2” disk to QSC, or by
logging on to QSC Online and downloading the appropriate files.
Test Point Schedule
The following test points are described for testing and troubleshooting references. These test
points are universal among all models. Actual voltages and current readings will vary.
AMPLIFIER SECTION
J502 Bed of Nails (J602 is for channel 2):
Pin 1 Negative 15VDC IC Supply,
Pin 2 Positive 15VDC IC Supply.
Pin 3 No
Connection
Pin 4 Second Stage OpAmp.
Less than 1 00mVDC offset.
Pin 5 No Connection
Pin 6 Positive Switched Bus Rail.
Test signal superimposed on DC voltages.
Pin 7 No Connection.
Pin 8 Negative Switched Bus Rail.
Test signal superimposed on DC voltages.

T e s t & Calibration
NOTE: This test procedure will refer to the amplifier’s channels as Ch 1 (Channel 1) & Ch2
(Channel 2). Component designation will have the prefix “5”for Ch 1 and “6” for Ch2.
CX4 / CX4T Test Procedure
l SET-UP
1. Connect a test load to the output terminals of the amplifier.
2. Make sure the Stereo / Bridge switch is set to the Stereo position.
3. Connect a distortion analyzer with a resolution of 0.05%, 20-20kHz (or better) to the output
terminals of the amplifier. Enable the 80kHz low pass filter.
4. Connect a dual-channel oscilloscope to the following test points:
Ch1 - a 10X (vertical sensitivity - 2V/cm) scope probe to the channel speaker output.
Ch2 - a 1X scope probe (vertical sensitivity - 0.1V/cm) to the distortion analyzer
output.
5. Set amp gain pots fully clockwise and turn on power switch.
6. Connect the output of the signal generator to the input terminals of the amplifier and select
an output of 0.96 (0.98 for CX4T) VRMS, 1 KHz sine wave.
7. Plug the amplifier in to a variac and set up an AC line current monitor.
lPOWER 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 240V. Pause at 90VAC (200VAC
European) for three seconds until the mute / protect circuit disengages. Continue to 120VAC
(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.
l 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 observing
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 170 watts at 1 kHz just beyond the point of clipping (1 .0% THD+N). Check both
channels.
l BIAS ADJUSTMENT
1. Let the amplifier cool down to room temperature.
2.With an input amplitude of 1Vrms increase the input frequency to 15kHz. Reduce the input
signal 20dB (80%) from full output. For the first channel to be calibrated, adjust the crossover
trimpot R512 for about a 400mVpk-pk crossover spike protruding from the noise trace on
the oscilloscope. It will be necessary to have the oscilloscope measure unfiltered distortion

CX Series
from the amplifier in order to see the crossover spike. It is necessary to disable the 80kHz
lowpass filter on the analyzer for this test. Further trim R512 so that the total distortion for
that channel is at about 0.1% THD+N. If bias is not adjustable, see the bias description and
troubleshooting section of this manual,
3. If a distortion analyzer is not available, a less accurate crossover distortion and bias adjustment
can be made by monitoring the driver transistor (Q503 & 0504) bias current. With the
amplifier at room temperature, and with no input signal plugged into the amplifier, measure the
DC voltage across the emitter resistors of 0502 or Q504 (R516, R517). Adjust R512 to
obtain about 80mV d.c. across one of these resistors.
4. With no signal plugged into the amplifier and with an 8 ohm load, verify that the AC idle
current from the AC service is no more than 1 .O amps a.c.
5. Let the amplifier cool down and check / adjust channel 2.
l SHORT CIRCUIT CURRENT
1. Select a 4 ohm load and apply a 1Vrms sinewave (1 kHz) input signal to both channels of the
amplifier. Ensure that power is on and that the gain controls are fully up.
2. While the amplifier is producing power into the loads, apply a short to the output binding posts
of each channel. In other words, apply a jumper between the red and black binding posts of
each channel. Once this is done, the combined AC line current draw for both channels
should be no greater than 7.5A ac. This is with a 120 volt AC service to the amplifier. Current
may be lower as AC line voltage is lower. As the amplifer heats up, current draw may increase
to about 9 amperes until thermal protect shutdown.
3. While the amplifier is driving a short, observe the main supply rail voltages. Ideally, they will be
no more than 3 volts from each other.
4. Remove the short from each channel and verify that the channels recover in to 4 ohm loads.
The output should not experience any hang up and a full sinewave should be present just as
it was before a short was applied for this test.
5. If the amplifier does not pass any of the above steps, follow the proceeding steps. If steps 2,
3, and 4 above pass, continue to the next test FREQUENCY RESPONSE.
Setting Short Circuit Current Limits
a. Select a 4 ohm load and apply a 1.2Vrms sinewave (1 kHz) input signal to both
channels of the amplifier. Ensure that power is on and that the gain controls are
fully up.
b. Turn gain controls on CH2 fully down. CH1 should be producing max power in the
4 ohm load.
c. While CH1 is delivering power into the load, apply a short across channel 1’s
binding posts.
d. Observe that the A.C. current draw is between 2.5 to 3.5 amps A.C.. Adjust R514
and R515 to get this current reading if your initial reading is off. R514 is the
positive current limit adjust and R515 is the negative current limit adjust Adjust
both 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 from 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 (I + or I - )until both polarities clip at the
same time.

g. After the short circuit current is set and even clipping is achieved, re-apply 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 CH1and calibrate CH2. It is important to calibrate
only one channel at a time.
l FREQUENCY RESPONSE
CX
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 20Hz 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 20Hz to 20kH.z). Check both channels,
CXT
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 45Hz to 16kHz (+/- 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 45Hz to 16kHz). Check both channels.
l POWER vs. DISTORTION TEST
CX
1. Check to ensure that both channels will produce rated power at 20Hz, 2KHz, and 20kHz. into
an 8 ohm load.
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.
CXT
1. Check to ensure that both channels will produce rated power at 45Hz, 2KHz and 16kHz. into
an 8 ohm load.
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 (70V, 100V) 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 in to 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 recovery.
l OUTPUT NOISE
1. Set the amplifier gain controls all the way up, with a 1 kHz 1.00Vrms sinewave input signal.
Note the output level.
7

CX Series
2. Remove the input signal connector from the amplifier and measure the residual noise level
produced into the load by the amplifier. The noise signal should be 100 dB down from the
full output power point measured. A signal to noise ratio should be better than or equal to
100dB. Check both channels.
l 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.
CX6 / CX6T Test Procedure
l SET-UP
1. Connect a test load to the output terminals of the amplifier.
2. Make sure the Stereo / Bridge switch is set to the Stereo position.
3. Connect a distortion analyzer with a resolution of 0.05%, 20-20kHz (or better) to the output
terminals of the amplifier. Enable the 80kHz low pass filter.
4. Connect a dualchannel oscilloscope to the following test points:
Ch1 - a 10X (vertical sensitivity - 2V/cm) scope probe to the channel speaker output.
Ch2 - a 1X scope probe (vertical sensitivity - 0.1V/cm) to the distortion analyzer
output.
5. Set amp gain pots fully clockwise and turn on power switch.
6. Connect the output of the signal generator to the input terminals of the amplifier and select
an output of 1.15 VRMS, 1 KHz sine wave.
7. Plug the amplifier in to a variac and set up an AC line current monitor.
lPOWER 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 240V. Pause at 90VAC (200VAC
European) for three seconds until the mute / protect circuit disengages, Continue to 120VAC
(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.
l 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 220 watts at 1 kHz just beyond the point of clipping (1.0% THD+N). Check both
channels.
l 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 (CH1 positive and CH2 negative).
4. Apply a 1VRMS, 1 kHz sinewave input to channel 1 of the amplifier. Check for 600 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.

CX Series
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.
l BIAS ADJUSTMENT
1. Let the amplifier cool down to room temperature,
2. With an input amplitude of 1Vrms, increase the input frequency to 20kHz. Reduce the input
signal 20dB (80%) from full output. At this point, a couple of watts of output power should be
observed at the output.For the first channel to be calibrated, adjust the crossover
trimpot
VR501 for about a 400mVpk-pk crossover spike protruding from the noise trace on the
oscilloscope. It will be necessary to have the oscilloscope measure unfiltered distortion from
the amplifier in order to see the crossover spike.It is necessary to disable the 80kHz lowpass
filter on the analyzer for this test. Further trim
VR501 so that the total distortion for that
channel is at about 0.1% THD+N. If bias is not settable, see the bias description and
troubleshooting section of this manual.
3. If a distortion analyzer is not available, a less accurate crossover distortion and bias adjustment
can be made by monitoring the driver transistor (Q501 & Q502) bias current. With the
amplifier at room temperature, and with no input signal plugged into the amplifier, measure the
DC voltage across the emitter resistors of Q501 and Q502 (R501, R502). Adjust VR501 to
obtain about 80mV d.c. across one of these resistors.
4. With no signal plugged into the amplifier and with an 8 ohm load, verify that the AC idle
current from the AC service is no more than 1 .O amps a.c.
5. Let the amplifier cool down and check/adjust channel 2.
l SHORT CIRCUIT CURRENT
1. Select a 4 ohm load and apply a 1Vrms sinewave (1 kHz) input signal to both channels of the
amplifier. Ensure that power is on and that the gain controls are fully up.
2. While the amplifier is producing power into the loads, apply a short to the output binding posts
of each channel. In other words, apply a jumper between the red and black binding posts of
each channel. Once this is done, the combined AC line current draw for both channels
should be no greater than 8.0A ac. This is with a 120VAC service. Current may be lower as
AC line voltage is lower. As the amplifier heats up, current draw may increase to about 9A until
thermal protect shutdown.
3. While the amplifier is driving a short, observe the main supply rail voltages. Ideally, they will be
no more than 3 volts from each other.
4. Remove the short from each channel and verify that the channels recover in to 4 ohm loads,
The output should not experience any hang up and a full sinewave should be present just as
it was before a short was applied for this test.
5. If the amplifier does not pass any of the above steps, follow the proceeding steps.
If steps 2,
3, and 4 above pass, continue to the next test “Frequency Response. ”
Setting Short Circuit Current Limits
a. Select a 4 ohm load and apply a 1 .2Vrms sinewave (1 kHz) input signal to both
channels of the amplifier. Ensure that power is on and that the gain controls are
fully up.
b. Turn gain controls on CH2 fully down. CH1 should be producing max power in the
4 ohm load.
c.While CH1 is delivering power into the load, apply a short across channel 1’s
binding posts.
d. Observe that the A.C. current draw is 3.0 - 4.0 amps A.C.. Adjust VR502 and
VR503 to get this current reading if your initial reading is off. VR503 is the positive
current limit adjust and VR502 is the negative current limit adjust. Adjust both
channels the same for a change in current limiting. Both wipers need to adjust
evenly to achieve a balanced setting.
9

CX Series
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, re-apply 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 CH1 and calibrate CH2. It is important to calibrate
only one channel at a time.
l 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 20Hz 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 20Hz to 20kHz). The frequency extremes for the CX6Tdirect
outputs is between 45Hz and 16kHz (-3dB @ 45Hz, -0.2dB @ 20 kHz). Check both channels.
l POWER vs. DISTORTION TEST
1. Check to ensure that both channels will produce rated power at 20Hz, 2KHz, and 20kHz. into
an 8 ohm load. For the CX6T under test, check power levels between 200Hz, 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 (70V, 100V)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 in to 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 recovery.
l OUTPUT NOISE
1. Set the amplifier gain controls all the way up, with a 1 kHz 1 .00Vrms sinewave input signal.
Note the output level.
2. Remove the input signal connector from the amplifier and measure the residual noise level
produced into the load by the amplifier. The noise signal should be 100 dB down from the
full output power point measured. A signal to noise ratio should be better than or equal to
1OOdB. Check both channels.

CX Series
l 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.
CX12 / CX12T Test Procedure
l SET-UP
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 80kHz low pass filter.
Connect a dualchannel oscilloscope to the following test points:
Ch1 - a 1 OX (vertical sensitivity - 2V/cm) scope probe to the channel speaker output.
Ch2 - a 1 X scope probe (vertical sensitivity - 0. 1V/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.
lPOWER 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 for240VPause at 90VAC (200VAC
European) for three seconds until the mute / protect circuit disengages, Continue to 120VAC
(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.
l 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.
l 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 (CH1 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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CX Series
l BIAS ADJUSTMENT
1. Let the amplifier cool down to room temperature.
2. With an input amplitude of 1Vrms, increase the input frequency to 20kHz. Reduce the input
signal 20dB (80%) from full output. At this point, a couple of watts of output power should be
observed at the output.For the first channel to be calibrated, adjust the crossover trimpot
VR501 for about a 4OOmVpk-pk crossover spike protruding from the noise trace on the
oscilloscope. It will be necessary to have the oscilloscope measure unfiltered distortion from
the amplifier in order to see the crossover spike.It is necessary to disable the 80kHz lowpass
filter on the analyzer for this test. Further trim VR501 so that the total distortion for that
channel is at about 0.1% THD+N. If bias is not settable, see the bias description and
troubleshooting section of this manual.
3. If a distortion analyzer is not available, a less accurate crossover distortion and bias adjustment
can be made by monitoring the driver transistor (Q501 & Q502) bias current. With the
amplifier at room temperature, and with no input signal plugged into the amplifier, measure the
DC voltage across the emitter resistors of Q501 and Q502 (R501, R502). Adjust VR501 to
obtain about 80mV d.c. across one of these resistors.
4. With no signal plugged into the amplifier and with an 8 ohm load, verify that the AC idle
current from the AC service is no more than 1 .O amps a.c.
5. Let the amplifier cool down and check/adjust channel 2.
l SHORT CIRCUIT CURRENT
1. Select a 4 ohm load and apply a 1 Vrms sinewave (1 kHz) input signal to both channels of the
amplifier. Ensure that power is on and that the gain controls are fully up.
2. While the amplifier is producing power into the loads, apply a short to the output binding posts
of each channel. In other words, apply a jumper between the red and black binding posts of
each channel. Once this is done, the combined AC line current draw for both channels
should be no greater than 8.0A ac. This is with a 120VAC service. Current may be lower as
AC line voltage is lower. As the amplifier heats up, current draw may increase to about 9A until
thermal protect shutdown.
3. While the amplifier is driving a short, observe the main supply rail voltages. Ideally, they will be
no more than 3 volts from each other.
4. Remove the short from each channel and verify that the channels recover in to 4 ohm loads.
The output should not experience any hang up and a full sinewave should be present just as
it was before a short was applied for this test.
5. If the amplifier does not pass any of the above steps, follow the proceeding steps. If steps 2,
3, and 4 above pass, continue to the next test “Frequency Response. ”
Setting Short Circuit Current Limits
a, Select a 4 ohm load and apply a 1.2Vrms sinewave (1 kHz) input signal to both
channels of the amplifier. Ensure that power is on and that the gain controls are
fully up.
b. Turn gain controls on CH2 fully down. CH1 should be producing max power in the
4 ohm load.
c. While CH1 is delivering power into the load, apply a short across channel l’s
binding posts.
d. Observe that the A.C. current draw is 5.0 - 6.0 amps A.C.. Adjust VR502 and
VR503 to get this current reading if your initial reading is off. VR503 is the positive
current limit adjust and VR502 is the negative current limit adjust. Adjust both
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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 CH1 and calibrate CH2. It is important to calibrate
only one channel at a time.
l 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 200Hz 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 200Hz to 20kHz). The frequency extremes for the CX6Tdirect
outputs is between 45Hz and 16kHz (-3dB @ 45Hz, -0.2dB @20 kHz). Check both channels.
l POWER vs. DISTORTION TEST
1. Check to ensure that both channels will produce rated power at 200Hz, 2KHz, and 20kHz. into
an 8 ohm load. For the CX6T under test, check power levels between 200Hz, 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 (70V, 100V) 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 recovev.
13

CX Series
l OUTPUT NOISE
1. Set the amplifier gain controls all the way up, with a 1 kHz 1 .00Vrms sinewave input signal,
Note the output level.
2. Remove the input signal connector from the amplifier and measure the residual noise level
produced into the load by the amplifier. The noise signal should be 100 dB down from the
full output power point measured. A signal to noise ratio should be better than or equal to
1 00dB. Check both channels.
l 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.