QSC CX4, CX6, CX12 Service Manual

CX Series

CX4

CX12

CX4T

CX Series

CX1

2T

CX SERIES AMPLIFIER

SERVICE MANUAL

CX4 CX6 -

CX12 -

QSC Technical Services

Wats:

Local: 1-714-957-7150 Fax: 1-714-754-6173

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

CX4T CX6T

CX12T

1-800-772-2834

http://www.qscaudio.com

CX Series Chassis Drawings

CX4

Chassis Assembly

CX4T

Chassis Assembly

CX6 &

CX6T &

CX 4 / 4T

CX 6T &

CX4 /4T

CX6

CX12

Chassis

CX12T

Series Main Amplifier Board

/6T

Series Main Amplifier Board

/12T

Chassis

Display Board Schematic

12T

Display Board Schematic

Series Main Amplifier Board

CX Series Wiring Diagrams

CX4

Wiring Diagram

CX4

Wiring Diagram

CX4

Wiring Diagram

CX4T

Wiring Diagram

....................................................................

..................................................................

Assemblyy........................................................

Assemblyy

(120v)) (100v)) (230v))

(120v))

..............................................................

....................................................

..................................................

.............................................

.................................................

................................................

..............................................

............................................................

42

45

48

39

40

41

42

56

57

58

59

CX4T

Wiring Diagram

CX4T

Wiring Diagram

CX6 Wiring Diagram

CX6T

Wiring Diagram

CX6T

Wiring Diagram

CX6T

Wiring Diagram

CX12

Wiring Diagram

CX12 Wiring

CX12 Wiring Diagram

CX12T CX12T CX12T

Diagram

Wiring Diagram

(100v))

(230v)) (120v)) (100v)) (230v)

(120v))

(100v)

(230v)

(120v)

(100v))

(230v))

(120v) (100v))

(230v))

............................................................

..............................................................

.............................................................

..............................................................

.............................................................

...........................................................

60

61

62

63

64

65

66

67

68

69

70

71

72

73

.e

*-“-”

.a’-

-ww.,_- ~

*“arT‘

-2

CX Series

CX Series Product Specifications

CX6

cx4

Output Power (per channel):

Continuous Average Output Power both channels driven:

8

ohms,

20Hz

-

20kHz,

0.1%

THD

4

ohms,

20Hz

-

20kHz,

0.1%

THD

2

ohms,

1kHz,

1%

THD*

Continuous Average Output Power bridged mono 8 ohms, 4 ohms, 1

Voltage Gain Sensitivity (for rated power

Distortion: SMPTE-IM Frequency Response: Damping Factor Noise: Input Impedance Dimensions Faceplate Faceplate Chassis Depth Weight Shipping, Net,

20Hz

Lbs/kg

-

20kHz,

kHz,

1% THD*

(@

direct outputs):

Width Height

Lbs/kg

0.1% THD

@

(@

direct outputs):

8 ohms):

150

watts

225

watts

350

watts

oDeration:

450 watts 700 watts 35x (31

dB)

0.96 V rms

Less than 0.05% 20Hz

to 200 1

00dB

below rated output (20 Hz to 20

10k

unbalanced, 20k balanced

Standard

3.5” (13.3 cm)

17.9” (45.5 cm)

36/16.4 30/13.6

200 300

4500

600 watts 400 watts 40x 1

.02

20kHz, +/-0.2dB

19”

Rack Mounting

5.25” (13.3 cm)

17.9” (45.5 cm)

53/24 44/20

CX12

watts 400watts watts

watts

(32

dB)

Vrms

650

watts

650

watts

1200 watts 1800 watts

56.5 (35 1

.00

Vrms

kHz)

5.25” (13.3 cm)

17.9” (45.5 cm)

58/26.3

50122.7

dB)

CX4 T

CX12T

CX Series Product Specifications

CX Series

CX4T

Output Power (per channel):

Direct Output, watts per channel, both channels driven: 8 ohms, 45H.z 4 ohms, 2 ohms, 1 Isolated outputs, watts per channel, both channels driven:

70V or 70V or 100V,

25V, 45Hz-16kHz, 25V,

1 Direct Outputs, bridged mono: 8

ohms, 45

4 ohms,

Voltage Gain

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,

Net,

Lbs/kg

-

20kHz,

0.1% THD

45Hz

-

20kHz,

0.1% THD

kHz,

1%

THD*

100V,

45Hz-16kHz,

1

kHz,

0.25% THD

kHz,

0.1% THD

Hz-20kHz,

1kHz,

1% THD

(dB):

Lbs/kg

0.25% THD

0.1% THD

150 watts 225 watts 350 watts

175 watts

150 watts

450 watts 700 watts

35x (31

dB)

0.98 V rms

Less than 0.05%

-3dB @

45Hz*,

45Hz* -16kHz, +0,

*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

10k ohms unbalanced and 20k balanced

Standard

3.5” (13.3 cm)

17.9” (45.5 cm)

46/21 40/18.2

CX6T

200 watts 300 watts

450 watts

250 watts

600 watts 900 watts

40x

1.02 Vrms

-0.2dB

@ 20kHz ; direct outputs

3dB ; isolated outputs

19”

Rack Mounting

5.25”

17.9”

62/28 55/25

(32

dB)

(13.3 cm) (45.5 cm)

CX12T

400 watts 600 watts 900 watts

500 watts

1200 watts 1800 watts

56.5x

(35

dB)

1 .00 Vrms

kHz)

5.25” (13.3 cm)

17.9”

(45.5 cm)

75/34 67/30.4

CX Series

I

n t r

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.

o

d u c t i o n

A

CAUTION: To reduce the risk of electric shock, do not remove the cover. No 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.

Equivalent Parts

Although many of the electronic components used in this product may be available from electronic suppliers, some components are specially tested and approved by

repaired with non-QSC supplied components may not meet factory specifications. performed using non-QSC parts may void the product warranty, When in doubt, you may contact

QSC

Technical Services for assistance.

A

user-

QSC.

A product

Repairs

Parts orders to part number (from the parts list in this manual). Parts will be shipped via UPS, 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

should include the product model number, the part description, and the QSC

F.O.B.

Costa Mesa,

QSC

Technical Services may be reached at (800) 772-2834.

3

Test Equipment

For testing, as outlined in this manual, the following equipment will be needed.

CX Series

REQUIRED TEST EQUIPMENT

-

Distortion Analyzer capable of 0.05% THD+N

-

High Power Load Bank (8, 4, & 2 ohms) for CX

-

High Power Load Bank

-

Function Generator

-

20MHz Oscilloscope

-

Digital

Multimeter

-

Variac

(0-l 40

VAC, 20-30A)

(40,20,

& 10 ohms) for CX T

Audio Precision test and procedures files are made available, free of charge, from Services by either sending a self addressed stamped envelope and a 3 logging on to

QSC

Online and downloading the appropriate files.

SUGGESTED TEST EQUIPMENT

*

Audio Precision System One

-

Thermocouple probe

QSC

Technical

1/2”

disk to

QSC,

or by

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

Pin 1 Negative

2

Positive

Pin 3 No

Less than Pin Pin 6 Positive Switched Bus

Connection

4 Second Stage

1

00mVDC

5 No

Connection

Test

signal superimposed

7 No Connection. 8 Negative Switched Bus

Test

signal

(J602

is for channel 2):

15VDC IC

superimposed on DC voltages.

Supply,

Supply.

OpAmp.

offset.

Rail.

on DC voltages.

Rail.

T e s t

&

Calibration

NOTE: This test procedure will refer to the amplifier’s channels as Ch 1 (Channel

(Channel 2).

CX4 /

l SET-UP

2.

3.

4.

5.

6.

7.

l POWER UP

2.

Component designation

CX4T

1.

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

terminals of the amplifier. Enable the 80kHz low pass filter.

Connect a

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 0.96 (0.98 for

Plug the amplifier in to a variac and set up an AC line current monitor.

1.

Slowly raise the variac voltage and watch for excessive current draw (Line current greater

than 0.5A European) for three seconds until the mute / protect circuit disengages. Continue to (240V European).

Turn the power switch off and on a few times to verify the 1 - 3 second power-up muting

delay. Check both channels.

Test Procedure

dual-channel

Ch1

-

a

10X

(vertical sensitivity Ch2 - a 1X scope probe (vertical sensitivity output.

&

MUTE DELAY TEST

a.c.

at 60 Volts). This is

will

have the prefix “5” for Ch 1 and “6” for Ch2.

0.05%,

20-20kHz (or better) to the output

oscilloscope to the following test points:

CX4T) VRMS,

slightly less

2V/cm)

1 KHz sine wave.

scope probe to the channel speaker output.

0.1V/cm)

for 240V. Pause at

to the distortion analyzer

90VAC (200VAC

1)

& Ch2

120VAC

l CHANNEL OUTPUT

1.

Look for amplified signal on the scope for channel

channel 2 and repeat output test. Check for noisy 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 channels.

l BIAS ADJUSTMENT

1. Let the amplifier cool down to room temperature.

2. With an input amplitude of

signal 20dB (80%) from full output. For the first channel to be calibrated, adjust the crossover trimpot R512 the oscilloscope. It will be necessary to have the oscilloscope measure unfiltered distortion

for about a

kHz

just beyond the point of clipping (1 .0%

1Vrms

400mVpk-pk

1.

Switch the input signal and scope to

/

contaminated gain pots by observing

THD+N).

increase the input frequency to

crossover spike protruding from the noise trace on

15kHz.

Check both

Reduce the input

from the amplifier in order to see the crossover spike. It is necessary to disable the 80kHz lowpass that troubleshooting section of

3.

If a distortion analyzer is

filter on the analyzer for this test. Further trim

channel is at about 0.1% THD+N. If bias is

this

manual,

not

available, a less accurate crossover

not

adjustable, see the bias description and

can be made by monitoring the driver transistor (Q503 & amplifier at room temperature, and with no input signal plugged

DC voltage across the emitter resistors of

obtain about 80mV

4.

With no signal plugged

d.c.

current from the AC service is no more than 1 .O amps

5.

Let the amplifier cool down and check / adjust channel

l SHORT CIRCUIT CURRENT

1. Select a 4 ohm load and apply a

across one of these resistors.

into the

amplifier and with an 8 ohm load, verify that the AC idle

1Vrms sinewave

0502

or Q504 (R516,

(1

kHz)

a.c.

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 of each channel. In other words, apply a jumper between the red and black binding posts of each channel. Once should be no greater than

this

is done, the combined AC line current draw for both channels

7.5A

ac.

This is with a 120

volt 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

4. Remove The output should

the

short from each channel and verify that the channels recover in to 4 ohm loads.

not

experience any hang up and a full

other.

it was before a short was applied for this test.

5.

If the amplifier does

3, and 4 above pass, continue to the next

not

pass any of

the

above steps, follow the proceeding

test

FREQUENCY RESPONSE.

R512

so that the total distortion for

distortion

0504)

bias current. With the

into

R517).

and bias adjustment

the amplifier, measure the

Adjust

R512

to

2.

input signal to both channels of the

the

output binding posts

AC service to the amplifier. Current

sinewave

should be present

steps.

If steps 2,

just

as

CX Series

Setting Short Circuit Current

a.

Select a 4 ohm load and apply a

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.

4 ohm load.

c.

While

CH1

is delivering power into the load, apply a

binding posts.

d.

Observe that the

and R515 to

get

this current reading if your initial reading is off. R514 is the

positive current limit adjust and

both channels

the

adjust evenly to achieve a balanced setting.

e.

Once the correct AC current draw is

this is done, not,

the current limits are set too low.

f,

Once the

output

the output

output

sinewave

recovers

adjust the current limit for that polarity (I + or I same time.

Limits

1.2Vrms sinewave

CH1

A.C.

current draw is between 2.5 to 3.5 amps

R515

is the negative current limit adjust Adjust

(1

kHz)

input signal to

both

should be producing max power in the

short

across channel

A.C..

1’s

Adjust

R514

same for a change in current limiting. Both wipers need to

set,

remove the short from

the output

When

power should spring back into the 4 ohm load. If it does

into

the 4 ohm load, verify that

both

polarities of the

are clipping at the same time. If one polarity clips before the other,

-

) until

both

polarities clip at the

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

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 between these extremes. This is done by verifying the same voltage amplitude at each of

the frequencies selected (within 45Hz to

l POWER vs. DISTORTION TEST

CX

1. Check to ensure that both channels will produce rated power at 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

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 or 10 ohm loads to ensure that both channels will produce rated power at

16kHz.

16kHz (+/-

16kHz).

Check both channels.

0.2dB) by sweeping random frequencies

20Hz,

2KHz,

and

45Hz, 2KHz

(70V,

100V) with 40 ohm, 20 ohm,

and

45Hz, 2kHz,

20kHz.

16kHz.

and

into

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

3.

Verify that the PTC circuit causes thermal shutdown after an extended period of time.

C.

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

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.

CX Series

CX6 /

l SET-UP

l POWER UP

CX6T

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

terminals of the amplifier. Enable the 80kHz low pass filter.

4. Connect a dualchannel oscilloscope to the following test points:

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

7. Plug the amplifier in to a variac and set up an AC line current monitor.

1.

Slowly raise the variac voltage and watch for excessive current draw (Line current greater

than 0.5A

European) for three seconds until the mute

(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.

Test Procedure

Ch1

-

a

10X

(vertical sensitivity Ch2 - a 1X scope probe (vertical sensitivity output.

VRMS,

1 KHz sine wave.

&

MUTE DELAY TEST

a.c.

at 60 Volts). This is slightly

2V/cm)

scope probe to the channel speaker output.

less

for

/

protect circuit disengages, Continue to

0.05%,

0.1V/cm)

240V.

20-20kHz (or better) to the output

to the distortion analyzer

Pause at

90VAC (200VAC

120VAC

l CHANNEL OUTPUT

1. Look for amplified signal on the scope for channel 1.

channel 2 and repeat output test. Check for noisy 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 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

4.

Apply a

0.1% THD+N and verify that the output does not collapse. The position of does not affect the output level.

1VRMS,

1

kHz sinewave

kHz

just beyond the point of clipping (1.0%

input to channel 1 of the amplifier. Check for 600 watts at

Switch the input signal and scope to

.

/

contaminated gain pots by looking for

THD+N).

(CH1

positive and CH2 negative).

CH2’s

Check both

gain control

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 signal 20dB (80%) from full output. At this point, a couple of watts of output power should be observed at the output. VR501 for about a

400mVpk-pk

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 filter on the analyzer for this test. 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 amplifier at room temperature, and with no input signal plugged into the amplifier, measure the DC voltage across the emitter resistors of obtain about 80mV

d.c.

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

5.

Let the amplifier cool down and check/adjust channel 2.

1Vrms,

increase the input frequency to 20kHz. Reduce the input

For the first channel to be calibrated, adjust the crossover

crossover spike protruding from the noise trace on the

Further trim

VR501

(Q501 & Q502)

Q501

and

so that the total distortion for that

bias current. With the

Q502

(R501,

R502).

across one of these resistors.

a.c.

Adjust

trimpot

lowpass

VR501

to

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. 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

VR503 to get this current reading if your initial reading is off.

A.C.

current draw is 3.0 - 4.0 amps

A.C..

Adjust

VR503

VR502

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.

If steps 2,

and

9

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

adjust the current limit for that polarity (1

same time.

g.

After the short circuit current is set and even clipping is achieved,

to the output to reconfirm AC line current. If the current draw is not within the

range specified, again balance the current limit

correct AC current draw is met.

h. Remove the input signal from

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

between these extremes, This is done by verifying the same voltage amplitude at each of

the frequencies selected (within

outputs is between 45Hz and

CX Series

are clipping at the same time. If one polarity clips before the other,

+

or I

-

) until both polarities clip at the

trimpots

CH1

and calibrate

20kHz

(+/- 0.2dB)

20Hz

to 20kHz). The frequency extremes for the

16kHz (-3dB @

45Hz,

-0.2dB @ 20

by sweeping random frequencies

until even clipping and the

CH2.

It is important to calibrate

kHz).

re-apply

Check both channels.

the short

CX6Tdirect

l POWER vs. DISTORTION TEST

1.

Check to ensure that both channels will produce rated power at

an 8 ohm load. For the 20kHz (-3dB @

2.

While verifying rated power, check that at all frequencies the distortion measurement is less

45Hz,

CX6T

under test, check power levels between

-0.2dB @ 16

kHz).

20Hz,

2KHz,

and 20kHz. into

200Hz,

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 or 10 ohm loads to ensure that both channels will produce rated power at

(70V,

100V) with 40 ohm, 20 ohm,

45Hz,

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.

2kHz,

and

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

l SET-UP

l POWER UP

/

CX12T

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 terminals of the amplifier. Enable the

4.

Connect a dualchannel oscilloscope to the following test points:

Set amp gain pots fully clockwise and turn on power switch.

5. Connect the output of the signal generator to the input terminals of the amplifier and select

6.

an output of 1 .00

7.

Plug the amplifier in to a variac and set up an AC line current monitor.

&

1.

Slowly raise the variac voltage and watch for excessive current draw (Line current greater

than 0.5A a.c. at 60 Volts).

European) for three seconds until the mute / protect circuit disengages, Continue to (240V European).

2. Turn the power switch off and on a few times to verify the 1

delay. Check both channels.

Test Procedure

80kHz

low pass filter.

Ch1

-

a 1 OX (vertical sensitivity -

Ch2 - a 1 X scope probe (vertical sensitivity - 0.

output.

VRMS,

1 KHz sine wave.

MUTE DELAY TEST

This

is slightly

2V/cm)

less

0.05%, 20-20kHz

scope probe to the channel speaker output.

1V/cm)

for 240V Pause at

(or better) to the output

to the distortion analyzer

90VAC (200VAC

-

3 second power-up muting

120VAC

l CHANNEL OUTPUT

1. Look for amplified signal on the scope for channel 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 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

the input connector from channel 2.

4. Apply a

0.1% THD+N and verify that the output does not collapse. The position of 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.

1VRMS,

1

kHz sinewave

kHz

just beyond the point of clipping (1 .0% THD+N). Check both

input to channel 1 of the amplifier. Check for 1200 watts at

Switch the input signal and scope to

1.

(CH1

positive and CH2 negative). Remove

CH2’s

gain control

11

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

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 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 obtain about 80mV

d.c.

across one of these resistors.

Q501

and

Q502 (R501, R502).

Adjust

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

5.

Let the amplifier cool down and check/adjust channel

a.c.

2.

trimpot

lowpass

VR501

CX Series

to

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

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.

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

VR503 to get this current reading if your initial reading is off. current limit adjust and

A.C.

current draw is 5.0 - 6.0 amps

VR502

1.2Vrms sinewave

CH1

should be producing max power in the

(1

kHz)

input signal to both

A.C..

Adjust

VR502

VR503

is the positive

is the negative current limit adjust. Adjust both

and

12

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

adjust the current limit for that polarity (1

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

correct AC current draw is met.

h.

Remove the input signal from

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 between these extremes. This is done by verifying the same voltage amplitude at each of

the frequencies selected (within

outputs is between

are clipping at the same time.If one polarity clips before the other,

+

or I

-

) until both polarities clip at the

45Hz

and

200Hz

16kHz

trimpots

CH1

and calibrate

to 20kHz

(+/-

0.2dB) by sweeping random frequencies

to 20kHz). The frequency extremes for the

(-3dB @

45Hz,

-0.2dB @ 20

until even clipping and the

CH2.

It is important to calibrate

kHz).

Check both channels.

CX6Tdirect

l POWER vs. DISTORTION TEST

1.

Check to ensure that both channels will produce rated power at

an 8 ohm load. For the CX6T under test, check power levels between 20kHz

2,

While verifying rated power, check that at all frequencies the distortion measurement is less

(-3dB @ 45Hz,

-0.2dB @ 16

kHz).

200Hz,

2KHz,

200Hz,

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 or 10 ohm loads to ensure that both channels will produce rated power at

(70V, 100V)

with 40 ohm, 20 ohm,

45Hz, 2kHz,

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

amperes.

6. Remove short to verify thermal protect

recovev.

and

2kHz,

20kHz.

and

2.5

into

13

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.

CX Series

.s ,.

.

CX Series

Troubleshooting

Current Draw

(Circuit breakers and fuses blow.Burning smell or smoke)

Symptoms:

-

Excessive current without signal present

l- Fast current draw

-

Medium current draw

. Slow current draw

-

Runaway current draw

Possible Causes:

-EXCESSIVE CURRENT WITHOUT SIGNAL PRESENT (Above 2A and less than 4A)

1.

The amplifier draws high current when the AC supply voltage is first applied. This symptom

may mean that there is a short in the power stages of the circuit.

2.

This could also be a misadjusted bias setting. See calibration procedures in this manual for

setting bias, Check for VR511, diodes

D505, D506, D605,

D606

VR61

(CX6/T,

1

(CX6/T,

CX1

CX12/T),

R512, VR612 (CX4/T)

2/T), D504, D505, D604,

D605

or open

(CX4/T).

l

FAST CURRENT DRAW (increases rapidly at only a few volts AC):

1.

Reversed or shorted main bridge rectifier

BR601, BR602

(CX12/T).

Check the bridge rectifier by setting DMV to diode mode. To verify

a good bridge rectifier, connect the negative lead to

0.4 to

0.6v

at both AC terminals. Connect positive lead to

BR501, BR601 (CX4/T, CX6/T), BR501, BR502,

BR+

(BR = bridge rectifier) and check for

BR-

and check for 0.4 to

0.6v

at

both AC terminal.

2. Both supply clamping diodes shorted or reversed D510, D512

3. Shorted or reversed C509, C510, C511, C512, C611,

l

MEDIUM CURRENT DRAW (increases slowly, can go to 30 VAC before current becomes excessive.):

1.

Single polarity driver or output short.

2.

Open or missing bias diodes

l

SLOW CURRENT DRAW (above 60 volts AC before current begins to increase, amp may pass signal):

1.

Severely misadjusted bias circuit or defective

(CX4/T).

C612

(CX6/T),

C511,

D505,

C512, C609, C610, C611,

C512, C513, C514, C611, C612,

D506

(CX6/T,

D512, D513, D612,

CX12/T),

D504,

D505-506 (CX6/T,

D613

C612

C613,

D505

CX12/T),

(CX6/T,

CX12/T),

(CX12/T),C511,

C614 (CX4/T).

(CX4/T).

R512, R612, D504,

D505 (CX4/T).

2.

Severe oscillation causing current drain. Check all feedback components and high frequency

snubber circuit

l RUNAWAY CURRENT DRAW

1.

A reversed filter capacitor: caution, may vent explosively.

(30-40V

AC before current begins to increase or runaway):

15

Protection, Standby, and Power Up.

(The amplifier locks up or does not startup and shut off correctly)

CX Series

Model

CX4/4

T

Symptoms:

l Amplifier does not come out of protect

-

Model

Amplifier

-

Muting delay

-

Pilot LED not working

-

Fan doesn’t work

CX6/6T &

will

not thermally protect

CX12/12T

Symptoms:

-

Amplifier does not come out of protect

*

Relay won’t turn on with normal operating amplifier

-

No RED “PROTECT” LED

-

No muting delay

l No thermal shutdown

l No DC protect

-

Shut off under signal

-

DC faults without current draw

l Fan doesn’t work

CX4/4

T Possible Causes:

l AMPLIFIER DOES NOT COME OUT OF PROTECT

1.

Q50 or Q51 shorted

2.

Voltage on Z5 should be

D51,

or open

3. Check for open LD50 and

base-collector

R51/R54.

junction or collectoremitter junction.

14v

-

1.5v.

If this voltage is low, check for leaky

PTCs R56, R57.

C51, C52,

defective

l AMPLIFIER WILL NOT THERMALLY PROTECT (If “Muting” circuit is OK)

1.

Check for shorted LD50 and

l MUTING DELAY

1. Excess muting delay (rest works OK): Check timing capacitor but circuit is slow to turn on, check

2. No muting delay (rest works OK):

l PILOT LED NOT WORKING

1,

Check for shorted or open pilot LD2

l FAN DOESN’T WORK

1.

Always operate at high speed: check open PTC

2. Always operate at low speed: check shorted PTC

base, emitter

3.

Doesn’t operate: missing

cold and 24V at

junction.

hot.

If voltage is OK, replace defective fan

PTCs R56, R57,

incorrect

R55, R53,

C51

D51.

R51/R51

R63

or high. Check voltage across fan terminal, should be 1 OV at

low ( fast charge

(CH1)

or LD4

(CH2).

R50,

C51).

Check

defective

or open

R50.

voltage. If it rises normally

Missing

R53

or high.

R531/R631.

U50,

shorted Q52.

U50,

Q52 shorted

CX Series

CX6/6T &

l AMPLIFIER DOES NOT COME OUT OF PROTECT

CX12/12T

1.

Check speaker bus for DC; if over 3VDC present, the protection circuit is operating normally

Possible Causes:

to hold of operation. See DC FAULT WITHOUT CURRENT DRAW section to fix this DC fault.

l RELAY WON’T TURN ON WITH NORMAL OPERATING AMPLIFIER:

1

.Check

Relay power voltage. With relay off, voltage at

With relay on,

2.

If relay power voltage OK; check voltage on the timing capacitor C515. Should rise to

12-15VDC,

3.Timing

voltage OK; check relay transistor

C516

should measure about

in three seconds, which triggers

Q512.

27V.

Q513.

C516

if not check

If not check

If good, RN501 B-C resistors from base to

speaker bus should activate relay.

4.

Relay driver

l NO RED “PROTECT” LED

1.

Check LED voltage, If over

LED), there is no “protect” power (open or missing

Q512

OK, check driver

Q513

and LD1 01.

-2V,

LED is defective. If OV with relay off (no negative voltage to

R534),

Be sure to correct before proceeding.

l NO MUTING DELAY (be sure “protect” LED works)

ALSO WITHOUT THERMAL OR DC PROTECT: relay or circuit is “stuck on’!

1,

Relay

Q512

shorted or wrongly mounted. Check by jumping base to emitter, should turn it

Off.

2.

Relay

Q513

shorted or wrongly mounted. Check by jumping base to emitter, should turn it

Off.

should measure about 47VDC.

D516, R531,

R528, R530, C515

C516,

D515.

polarity

which defeats shutdown circuits.

NO MUTING DELAY ONLY (all else OK):

1. D518 reversed ( charges timing capacitor

2. R528 low (fast

3.

R29

low (low voltage on E7 turns

C515

charge)

EXCESS MUTING DELAY:

1. Check timing capacitor D517

(lift temporarily),

E515

voltage, If it rises normally but circuit is slow to turn on, check

LD501

bad or intermittent, RN501 D too low.

2. Timing capacitor voltage wrong; determine cause wrong

Q511.

l NO THERMAL SHUTOFF

Short the amplifier load with full signal to raise R516

&

R616 (yellow or gray sensor on the output transistor), looking for voltage to rise from

cold to

l NO DC PROTECT:

5.5V

at shut down.

1.

No Red “Protect”, may have no

PTC).

Also check D517 high/missing, or relay drive circuit stuck on.

I.

R532

missing or very high.

2,

BR502 defective/wrongly stuffed

3. Q511

defective/wrong

4,

D518 reversed (also no muting delay)

C515

immediately)

Q513

on too soon), missing or high R30 (no off current).

(R528, R530,

heatsink

R531,

which defeats whole thermal circuit (no voltage across

temperature and put voltmeter across PTC

reversed

C515,

reversed or

0.7V

17

CX Series

5.

Replace

l SHUTS OFF UNDER SIGNAL

1. C517 missing, defective, or much too small

l DC FAULT WITHOUT CURRENT DRAW

In most cases, shorts in the output circuit will cause current draw, but certain shorts will only cause DC

offset in the output. In both cases, measure all the voltages, and look for abnormal values to help trace

the fault, which can be a solder or component short (zero volts), reversed zener or diode

reversed electrolytic (several volts), or wrong value parts (abnormal voltage).Look at the following points in the circuit.

I.

Shorted IC rails.

2.

Blown

3, VR502, VR503

4.

Collector-base short on the driver (rare without further damage)

5

Sometimes IC forces the rest of the circuit into DC due to shorts in the feedback network,

etc. To check this remove

VR502,

output stage is probably OK, look for problems in the

6.

Defective/reversed IC (pull and check voltage)

LD501

if voltage is less than

1.5V

(0.6V),

D521, D522

give zero volts on the IC rail.

turned all the way off or way too low in value.

IC,

check for

+/-15V,

and see if adjusting current limit trimmer

VR503 will produce a zero volt output (there will be no signal, of course). If so,

IC,

or its associated parts.

l FAN DOESN’T WORK:

1.

Always operate at high speed: check shorted fan thermal switch. (on the

main

PCB).

2. Always operate at low speed: check defective fan thermal switch.

3. Doesn’t operate: check open

R902

on the AC PCB and intermittent fan cable connectors.

Faults with Signal Present

(The amplifier passes a signal but is not running correctly)

Symptoms:

-

Output power “breaking up”

l -Ringing’ sound with no input to amplifier

-

Output collapses into a 8, 4, or 2 ohm load

-

Voltage rails ok without signal

-

Amplifier gets too hot without load

-

One channel clips prematurely

-

Gain wrong

-

Poor Frequency Response

l Step Circuit Problems

heatsink

under the

Possible Causes:

l OUTPUT POWER “BREAKING UP” (Output

1.

R523,

,524, 526, 527

2.

C513,

C514 open.

3.

Check for continuity between speaker ground, input ground and ac ground.

4. R501, R502, 5,

Current limits out of adjustment.

R543 open.

open

(CX4/T) R520.

(CX4/T) C515.

(CX4/T) R516, R517.

distorted

CX Series

6.

Defective gain control

l “RINGING’ SOUND WITH NO INPUT TO AMPLIFIER

1. C518, C519,

2. R541, R542, R538,

3.

Defective op amp

4. Unstable driver transistors (Q501, Q503, Q504,

l OUTPUT COLLAPSES INTO A LOAD

1. D519, D520,

2.

Misadjusted current limits

3.

Defective op amp

4.

R501, R502

C523 open or wrong value.

R547 open or wrong value.

U503. (CX4/T) U501

Q502),

and outputs

Q500Q502

&

Q505Q507.

R548 wrong value or open.

(VR502, VR503). (CX4/T) R513, R514.

U503. (CX4/T) U501.

wrong value.

(CX4/T) R516, R517.

(CX4/T) C505, C516.

or output transistors

(CX4/T)

(CX4/T) R523, R524, R502.

(Q505 -

D509, D511, R518.

Q510).

(CX4/T)

drivers

l VOLTAGE RAILS OK WITHOUT SIGNAL (Collapses

1. C525,

C526 leaky or not holding a charge.

wit

signa/)

(CX4/T) C506, C507.

2. Check for capacitance value of C520.

l AMPLIFIER GETS TOO HOT WITHOUT LOAD

1.

Bias

trimpot (VR501)

2. Incorrect bias diodes

3.

R517,

R518 open or has drifted in value.

4. Defective op amp

l ONE CHANNEL CLIPS PREMATURELY

1. R517

or R518 may be open or drifted in value.

2. Misadjusted current limits

3. Defective zener

4. Check for open

5. 680 ohm chargeback resistor R548 may be open.

l GAIN WRONG

misadjusted, opened or burned.

(D505,

506 should be 1

N4934). (CX4/T) D505, D506.

(CX4/T) R504,

U503. (CX4/T) U501.

(CX4/T) R504, R528.

(VR502, VR503). (CX4/T) R514, R515.

D511, D514. (CX4/T) D503, D506.

R512, R522, R539, R546. (CX4/T) R513,

(CX4/T) R518.

(CX4/T) R512.

R527.

R525,

1. Too high: Missing one of the two feedback resistors from output, R538 or R524;

or input

RN902, (CX4/T)

RN500 is wrong value. (Faulty input resistors will cause the

amplifier to fail the Common Mode test.)

2. Too low: Above feedback values wrong or shunt resistor

R541/C520,

open (open causes very low gain with instability. Check circuit trace).

l POOR FREQUENCY RESPONSE (Be sure to correct any gain problem first)

1.

High frequency, determined by feedback capacitor

C519, (CX4/T) C516

causes instability)

2.

Low frequency, determined by DC feedback rolloff

compensation network

C518/R542. (CX4/T)

C520,

and “butterworth” feedback

C502 low frequency

R503, R526.

R542, (CX4/T)

(CX4/T)

(wrong value also

rolloff.

R523 wrong or

l STEP CIRCUIT

(CX12/T

only) Check step circuit components step cuts in (are both matched to Check referent

1.

Step distortion: check step filter components

15V

zener voltages D509 and

U501, U502,

1V).

Q503,

Q504

carefully, note exact output voltage where

Step turning on too late (too high) will hang up at 2 ohms.

D510.

After inspecting all parts, see below:

R508/C505, R504/C501,

and

C528.

19

CX Series

2. No step: check

0503,

Q504,

U501,

U502 burned to open.

R505, R506,

R510 open.

Instability

(Gain problems, spurious noises, and oscillations)

All Models

l General Output Distortion l Excessive or unbalanced crossover

-

Output waveform appears “fuzzy”

Possible Causes:

First, distinguish between instability (fuzziness), “ringing” which is momentary instability after a transition,

l GENERAL OUTPUT DISTORTION

"step”

distortion, crossover

distortion

(both often show ringing), or general

distortion.

SEVERE: All loads, often with current draw: often associated with feed back components C520, C519,

C518,

C523). (CX4/T) U501,

C516,

C505.

Check resistor values on

R542, R568, R538, R547. (CX4/T) R502, R523, R524.

MEDIUM: Check feedback capacitor

C519. (CX4/T) C516,

(U503, C532,

R540, R541,

LOW GAIN: Suspect open circuit in feedback shunt

R541

and C520.

(CX4/T) R523.

Check for broken

circuit trace. Substitute IC and check IC socket for contamination.

l EXCESSIVE OR UNBALANCED CROSSOVER (Excess notch or ringing at zero crossing)

1.

Severe: shorted bias diode

D505, D506. (CX4/T) D504, D505.

2. Moderate: Out-of-spec bias diodes.

3.

Defective bias trimmer components VR501,

4.

Check for open base resistors

l OUTPUT WAVEFORM APPEARS ‘FUZZY

1. Check main

2.

High frequency snubbers defective (C513,

heatsink

ground continuity with chassis ground,

R517,

518 on output devices.

R511.

(CX4/T)

R512, R532.

(CX4/T) R504,

C514, R525, R526, R523,

R527.

R527).

(CX4/T) R520,

C515.

3.

Check capacitors on speaker output board.

4. Check/adjust driver emitter capacitors C519 and

C523. (CX4/T) C516, C505.

20

CX Series

Power Supply and Voltage Rail Balancing

(Uneven

Symptoms:

Possible Causes:

l CURRENT LIMITING WRONG

rails

and power supply problems)

-

Current limiting wrong

l Current limiting too high into a short

. IC rail too high into a short

-

Current limiting too low into a short

l Uneven voltage rails

Current limits should remain high down to 2 ohms, and collapse to a lower value for short circuits. This is caused by the IC rails going from normal 14 - 1.5 volts to about 5-6 volts. Current limit trimmers

TR502 & TR503

permits adjustment of each channel to a specified range.

See Test & Calibration Procedures for correct adjustment of the current limiting.

l CURRENT LIMITING TOO HIGH INTO SHORT (IC

1.

Reversed or shorted

2. Shorted bias diode

l

IC

RAIL TOO HIGH INTO SHORT

4.7V

zeners

D505,

D506 (also shows severe crossover).

D511, D514. (CX4/T) D503, D506.

rail

check

normal

5-6

volts)

(CX4/T) D504, D505.

1. Check op amp (weak output current).

2. Clip LED LD103 open, clip circuit parts R544 high or missing.

3.

D101/D102/D103/D104

l CURRENT LIMITING TOO LOW INTO SHORT AND 2 OHM LOAD

1.

Bias resistor

2,

Very low gain driver transistors.

3,

Missing connection or open emitter resistors in some of the paralleled output transistors.

.

CURRENT LIMITING TOO LOW INTO SHORT ONLY (OK into

1.

3.9 or

4.7V

zeners high

R512,

2. Clip LED LD103 shorted, clip circuit pans R544 low.

3. D101/D102/D103/D104 shorted.

l OK INTO SHORT BUT LOW INTO 2 OHMS:

1, IC

RAIL LOW: Check replenishing resistor R548 and diodes

open.

R522 high.

(7.5V

(CX4/T) BR500.

or

15V).

(CX4/T) BR500.

(Usually

(CX4/T)

on one side only)

(CX4/T) LD1, LD3, R511.

normal

loads)

LD1,

LD3, R511.

D519, D.520. (CX4/T) D509,

D511, R518.

2. IC RAIL OK: (until clipping starts) usually indicates low output section gain caused by weak driver, open output devices, or open emitter resistors. Also check value of driver emitter

resistors

R501, R502. (CX4/T) R516, R517.

UNBALANCED RAIL VOLTAGES:

1. Shorted

2.

Defective

3.

Open

4. Open

Q503,

Q504.

U501, U502.

R506, R505.

D514, D511. (CX4IT) D503, D506.

21

QSC CX4, CX6, CX12 Service Manual

Specifications and Main Features

Frequently Asked Questions

User Manual