QSC PLX Series Operating manual

Technical Service Manual
PLX™ Series
▲▲
▲▲
▲PLX 1202
▲▲
▲▲
▲PLX 1602
▲▲
▲▲
▲PLX 2402
▲▲
▲▲
▲PLX 3002
TD-000078-00
TD-000078-00

+ PLX 1202
+ PLX 1602
+ PLX 2402
+ PLX 3002

PLX SERIES
SERVICE MANUAL
PLX 1202
PLX 1602
PLX 2402
PLX 3002
QSC Technical Services
Wats: I -%OO-772-2034
Local: 1-714-957-7150
Fax: [phone]
QSC Technical Support BBS
I-714-668-7567
1-800-856-6003
QSC Audio Products, Inc.
1675 MacArthur Blvd.
Costa Mesa,
CA 92626
http://www.qscaudio.com

Table of Contents
PLX Product Specifications ................................................................
Introduction ........................................................................................
Test and Calibration ............................................................................
Troubleshooting PLX ...........................................................................
PLX Parts List
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PLX Semiconductors ..............................................................................
Chassis Drawings ...................................................................................
Schematics
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PLX Series PCB Circut Board Drawings .................................................
1
2
3
13
PLX 1202 PCB Assembly (120V) 23
PLX 1202 PCB Assembly (230V) 25
PLX 1202 Chassis Assembly (120V) 28
PLX 1202 Chassis Assembly (230V) 28
PLX 1602 PCB Assembly (120V) 28
PLX 1602 PCB Assembly (230V) 31
PLX 1602 Chassis Assembly (120V) 34
PLX 1602 Chassis Assembly (230V) 34
PLX 2402 PCB Assembly (120V) 35
PLX 2402 PCB Assembly (230V) 38
PLX 2402 Chassis Assembly (120V) 41
PLX 2402 Chassis Assembly (230V) 41
PLX 3002 PCB Assembly (120V) 42
PLX 3002 PCB Assembly (230V) 45
PLX 3002 Chassis Assembly (120V) 48
PLX 3002 Chassis Assembly (230V) 49
50
53
PLX 1202 Main PCB Schematics 57
PLX 1602 Main PCB Schematics 62
PLX 2402 Main PCB Schematics 67
PLX 3002 Main PCB Schematics 72
73

PLX Product Specifications
PLX 1202
PLX 1602
PLX 2402
PLX 3002
PLXI 202
PLXI 602
PLX2402
PLX3002
Output Power (per channel):
Continuous Average
Output Power bothchannelsdriven:
8 ohms,
2OHz - 2OkHz, 0.03% THD 200watts
4 ohms, 2OHz - 2OkHz, 0.05% THD
325 watts
Con0nuous Average Output Power bridged mono ooeration:
300 waKs
425watts 550watts
500 watts
700 watts 900watts
8 ohms,
2OHz - 2OkHz, 0.1% THD
Voltage Gain (dB)
Sensitivity (for rated power @8 ohms)
Distortion
Frequency Response (LF Switched Off)
Damping Factor (1 kHz and Below)
Noise
Input Impedance
Dimensions
FaceplateWidth
FaceplateHeight
ChassisDepth
Weight
Net, Lbs/kg
700 iatts 1100 watts 1500 watts
32 32 32
1.00vrms 1.20 Vrms
1.50 Vrms
SMPTE-IM Less than 0.01%
2OHz to 2OkHz, +I-0.2dB
8Hz to 5OkHz, +Ol-3dB
Greater than 500
106dB below rated output (20 Hz to 20 kHz)
6k unbalanced,
12k balanced
2000 watts
32
1.70 vrms
Standard 19” Rack Mounting
3.Y 3.r
13.2Y 13.2v
2119.5 2119.5
3.5” 3.Y
13.2Y 13.2Y
2119.5
2119.5

Introduction
This manual is prepared to assist service personnel with the repair and calibration of PLX power
amplifiers
. The procedures described in this manual require advanced technical experience
and sophisticated audio test equipment.
CAUTION: To reduce the risk of electric shock,
do not remove the cover. No user-serviceable
parts inside. Refer servicing to qualified
personnel. CAUTION
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
WC. A
product repaired with non-WC supplied components may not meet factory specifications.
Repairs performed using non-QSC parts may void the product warranty. men 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. QSC Technical Services may be reached at (800)
772-2834.
Test and Troubleshooting Equipment
- Distortion Analyzer capable of 0.01% THD+N
- High Power Load Bank (8,4,8 2 ohms)
- Function Generator 8 Digital Multimeter
- 2OMHz Oscilloscope
- Variac (0-140 VAC, 30-40A)
-Audio Precision - System One
+ Thermometer
2

Test & Calibration
PLX 1202 Test Procedure
. SET-UP
1. Connect a test load to the output terminals of the amplifier.
2. Make sure Mode Switches 1
- 10 are in the default position (1 on, 10 on, all others off).
3. Connect a distortion analyzer with a resolution of
O.Ol%, 20-2OkHz (or better) to the
output terminals of the amplifier. Enable the
8OkHz low pass filter.
4. Connect a dual-channel oscilloscope to the following test points:
Chl
- a IOX (vertical sensitivity - 2V/cm) scope probe to the channel speaker output.
Ch2
- a IX scope probe (vertical sensitivity - O.lV/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 1.30
VRMS, 1 kHz sine wave.
7. Plug the amplifier into a variac and set up an AC line current monitor.
. POWER UP 8 MUTE DELAY TEST
CAUTION: To avoid damage to the main printed circuit board, place a 50 ohm 225W resistor (100 ohm,
240VAC) in series with the high
(+) lead on the AC cable during variac ramp up. If the switching power
supply has a shorted device at initial power up, this AC resistor pad will help prevent undue damage. After
the amplifier has been fully powered up via the variac, confirm that the amplifier has achieved
stable operation during idle. Remove AC power from the amplifier and disconnect the series
resistor for normal operation. Continue with the test
& calibration process.
I. 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
9OVAC
(2OOVAC European) for three seconds until the mute I protect circuit disengages.
Continue to 12OVAC (240V European).
2. Verify that the fan is operating at low speed.
3. Turn the power switch off and on a few times to verify the 3 second power-up muting
delay.
l CHANNEL OUTPUT
I. 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 that this amplifier is producing 200 watts at 1 kHz just
below the point of clipping. Check both channels.
l BRIDGE MODE
1. Turn the power switch off.
2. Set Mode Switch
#7 in the on position. The gain control, limiter, and filter switch positions
on CH2 are disabled with Mode Switch
#7 on.
3. Set load to both red output binding posts (CHI positive and CH2 negative).
4. Apply a 1.30 VRMS, 1 kHz sinewaveinput to channel I of the amplifier. Check the power
and verify that the output does not immediately collapse. Check for 700 watts at 8 ohms.

5. Turn power off and place the amplifier back into the Stereo mode with output
loads connected to each channel.
. BIAS
1. Let the amplifier cool down to room temperature.
2. With an input amplitude of
1.3OVrms increase the input frequency to 2OkHz. Reduce the
input signal 20dB (80%) from full output. Adjust the crossover
trimpot VR43 (CHl) and
VR166 (CH2) 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 so that
the total distortion for that channel is less than 0.1% THD+N.
3. With the trim settings achieved, and 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
amperes.
4. Let the amplifier cool down and check channel 2.
. SHORT CIRCUIT CURRENT
1. Select a 2 ohm load and apply a 1.3Vrms 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, combined AC line current draw for
both channels should be no greater than
13A ac. This is with a 120 volt AC service to
the amplifier. Current may be lower if AC line voltage is lower.
3. Remove the short from each channel and verify that the channels recover in to 2 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.
4. If the amplifier does not pass any of the above steps, troubleshoot the current limit
section of the amplifier. If steps 2, 3, and 4 above pass, continue to the next test
FREQUENCY RESPONSE.
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 2OHz to 20kHz (+I- 0.2OdB) by sweeping random
frequencies between these extremes. This is done by verifying the same voltage
amplitude at each of the frequencies selected (within
2OHz to 2OkHz). Check both
channels.
l POWER vs. DISTORTION TEST
I. Check to ensure that both channels will produce rated power at
2OHz, 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 0.03% THD.
l THERMAL TEST
1. Set input frequency to 1 KHz and short both channels while they are producing power into
a load.
2. Apply a short to the output of each channel.
3. AC line current draw should be about11 - 13.5 amperes for both channels. As the
amplifier gets hot, there will be some current drift upwards and the fan speed will
increase. This is not a problem as long as the case temperature on the output
transistors does not exceed
105 degrees C.
4

4. Verify that the NTC circuit causes thermal shutdown after an extended period.
5. When thermal shutdown occurs, verify AC idle current of less that 0.90 amperes
l CM TEST
1. Select an 8 ohm load and confirm that this amplifier is producing rated power.
2. Check the Common Mode of the amplifier by inserting a
1/4” input jack halfway into each
channel and observe about 6
dB of output voltage reduction. There will also be a 180
degree phase inversion at the output of the channel under test.
l OUTPUT NOISE
1. Set the amplifier gain controls all the way up, with a 1
kHz 1.3OVrms sinewave input
signal. Note the output level at full power just below clipping. Adjust gain if needed.
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 107
dB down
from the full output power point measured. A signal to noise ratio should be better than
or equal to
107dB. 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.
PLX 1602 Test Procedure
. SET-UP
1.
2.
3.
4.
5.
6.
7.
Connect a test load to the output terminals of the amplifier.
Make sure Mode Switches 1
- 10 are in the default position (1 on, 10 on, all others off)
Connect a distortion analyzer with a resolution of
O.Ol%, 20-20kHz (or better) to the
output terminals of the amplifier.Enable the 80kHz low pass filter.
Connect a dual-channel oscilloscope to the following test points:
Chl - a 1 OX (vertical sensitivity - 2V/cm) scope probe to the channel speaker output.
Ch2
- a IX scope probe (vertical sensitivity - O.lV/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 1.30
VRMS, 1 kHz sine wave.
Plug the amplifier into a variac and set up an AC line current monitor.
l POWER UP 8 MUTE DELAY TEST
CAUTION: To avoid damage to the main printed circuit board, place a 50 ohm 225Wresistor (100 ohm,
240VAC) in series with the high
(+) lead on the AC cable during variac ramp up. If the switching power
supply has a shorted device at initial power up, this AC resistor pad will help prevent undue damage. After
the amplifier has been fully powered up via the variac, confirm that the amplifier has achieved
stable operation during idle. Remove AC power from the amplifier and disconnect the series
resistor for normal operation. Continue with the test
& calibration process.
Slowly raise the variac voltage and watch for excessive current draw (line current
greater than
0.5A a.c at 60 Volts). T/I;s is s/;ghf/y less for 240V. Pause at 9OVAC
(2OOVAC European) for three seconds until the mute I protect circuit disengages.
Continue to 12OVAC (24OV European).
Verify that the fan is operating at low speed.

3. Turn the power switch off and on a few times to verify the 3 second power-up muting
delay.
. 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 that this amplifier is producing 300 watts at 1 kHz just
below the point of clipping. Check both channels.
. BRIDGE MODE
1. Turn the power switch off.
2. Set Mode Switch
#7 in the on position. The gain control, limiter, and filter switch positions
on CH2 are disabled with Mode Switch
#7 on.
3. Set load to both red output binding posts
(CHI positive and CH2 negative).
4. Apply a 1.30 VRMS, 1 kHz sinewaveinput to channel 1 of the amplifier. Check the power
and verify that the output does not immediately collapse. Check for 1000 watts at 8
ohms.
5. Turn power off and place the amplifier under test back into the Stereo mode with output
loads connected to each channel.
l BIAS
I. Let the amplifier cool down to room temperature.
2. With an input amplitude of
1.3OVrms increase the input frequency to 20kHz. Reduce the
input signal 20dB (80%) from full output. Adjust the crossover
trimpot VR43 (CHl) and
VR166 (CH2) 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 so that
the total distortion for that channel is less than 0.1% THD+N.
3. With the trim settings achieved, and 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
amperes.
4. Let the amplifier cool down and check channel 2.
l SHORT CIRCUIT CURRENT
1. Select a 2 ohm load and apply a 1.3Vrms 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, combined AC line current draw for
both channels should be no greater than
13A ac. This is with a 120 volt AC service to
the amplifier. Current may be lower if AC line voltage is lower.
3. Remove the short from each channel and verify that the channels recover in to 2 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.
4. If the amplifier does not pass any of the above steps, troubleshoot the current limit
section of the amplifier. If steps 2, 3, and 4 above pass, continue to the next test
FREQUENCY RESPONSE.
6

l FREQUENCY RESPONSE
I. 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
2OHz to 20kHz (+I- 0.2OdB) by sweeping random
frequencies between these extremes. This is done by verifying the same voltage
amplitude at each of the frequencies selected (within
2OHz to 20kHz). Check both
channels.
l POWER vs. DISTORTION TEST
1. Check to ensure that both channels will produce rated power at
2OHz, 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 0.03% THD.
l THERMAL TEST
1. Set input frequency to 1 KHz and short both channels while they are producing power into
a load.
2. Apply a short to the output of each channel.
3. AC line current draw should be about
II - 13.5 amperes for both channels. As the
amplifier gets hot, there will be some current drift upwards and the fan speed will
increase. This is not a problem as long as the case temperature on the output
transistors does not exceed 105 degrees
C.
4. Verify that the NTC circuit causes thermal shutdown after an extended period.
5. When thermal shutdown occurs, verify AC idle current of less that 0.90 amperes.
l CM TEST
1. Select an 8 ohm load and confirm that this amplifier is producing rated power.
2. Check the Common Mode of the amplifier by inserting a
1/4” input jack halfway into each
channel and observe about 6
dB of output voltage reduction. There will also be a 180
degree phase inversion at the output of the channel under test.
l OUTPUT NOISE
I. Set the amplifier gain controls all the way up, with a 1 kHz 1.3OVrms sinewave input
signal.
Note the output level at full power just below clipping. Adjust gain if needed.
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 107
dB down
from the full output power point measured. A signal to noise ratio should be better than
or equal to
107dB. 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
veri@
the amplifier’s operation before returning the product to service.
PLX 2402 Test Procedure
l SET-UP
1. Connect a test load to the output terminals of the amplifier.
2. Make sure Mode Switches 1
- 10 are in the default position (1 on, 10 on, all others off).

3. Connect a distortion analyzer with a resolution of O.Ol%, 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:
Chl
- a 1OX (vertical sensitivity - 2V/cm)scope probe to the channel speaker output.
Ch2
- a IX scope probe (vertical sensitivity - 0. IV/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 1.50
VRMS 1 kHz sine wave.
7. Plug the amplifier into a variac and set up an AC line current monitor.
l POWER UP & MUTE DELAY TEST
CAUTION: To avoid damage to the main printed circuit board, place a 50 ohm 225W resistor (100 ohm,
240VAC) in series with the high
(+) lead on the AC cable during variac ramp up. if the switching power
supply has a shorted device at initial power up, this AC resistor pad will help prevent undue damage. After
the amplifier has been fully powered up via the variac, confirm that the amplifier has achieved
stable operation during idle. Remove AC power from the amplifier and disconnect the series
resistor for normal operation. Continue with the test
& calibration process.
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 slight/y /ess fof 24OV.Pause at
9OVAC
(2OOVAC European) for three seconds until the mute / protect circuit disengages.
Continue to 12OVAC (24OV European).
2. Verify that the fan is operating at low speed.
3. Turn the power switch off and on a few times to verify the 3 second power-up muting
delay.
l CHANNEL OUTPUT
I. 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 that this amplifier is producing 425 watts at 1 kHz just
below the point of clipping. Check both channels.
l BRIDGE MODE
1. Turn the power switch off.
2. Set Mode Switch
#7 in the on position. The gain control, limiter, and filter switch positions
on CH2 are disabled with Mode Switch
#7 on.
3. Set load to both red output binding posts
(CHI positive and CH2 negative).
4. Apply a 1.30 VRMS, 1 kHz sinewave input to channel 1 of the amplifier. Check the power
and verify that the output does not immediately collapse. Check for 1500 watts at 8
ohms.
5. Turn power off and place the amplifier under test back into the Stereo mode with output
loads connected to each channel.
l BIAS
1. Let the amplifier cool down to room temperature.
2. With an input amplitude of
1.5OVrms, increase the input frequency to 2OkHz. Reduce the
input signal 20dB (80%) from full output. Adjust the crossover
trimpot VR43 (CHl) and
VR166 (CH2) 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 so that
the total distortion for that channel is less than 0.1%
THD+N,
3. With the trim settings achieved, and 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
amperes.
4. Let the amplifier cool down and check channel 2.
l SHORT CIRCUIT CURRENT
1. Select a 2 ohm load and apply a 1.3Vrms 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, combined AC line current draw for
both channels should be no greater than
13A ac. This is with a 120 volt AC service to
the amplifier. Current may be lower if AC line voltage is lower.
3. Remove the short from each channel and verify that the channels recover in to 2 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,
4. If the amplifier does not pass any of the above steps, troubleshoot the current limit
section of the amplifier. If steps 2, 3, and 4 above pass, continue to the next test
FREQUENCY RESPONSE.
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
2OHz to 20kHz (+/- 0.2OdB) by sweeping random
frequencies between these extremes. This is done by verifying the same voltage
amplitude at each of the frequencies selected (within
2OHz to 20kHz). Check both
channels.
l POWER vs. DISTORTION TEST
1. Check to ensure that both channels will produce rated power at
2OHz, 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 0.03%
THD.
l THERMAL TEST
1. Set input frequency to 1 KHz and short both channels while they are producing power into
a load.
2. Apply a short to the output of each channel.
3. AC line current draw should be about 11
- 13.5 amperes for both channels. As the
amplifier gets hot, there will be some current drift upwards and the fan speed will
increase, This is not a problem as long as the case temperature on the output
transistors does not exceed 105 degrees C.
4. Verify that the NTC circuit causes thermal shutdown after an extended period.
5, When thermal shutdown occurs, verify AC idle current of less that 0.90 amperes.
l CM TEST
I. Select an 8 ohm load and confirm that this amplifier is producing rated power.
2. Check the Common Mode of the amplifier by inserting a
114” input jack halfway into each
channel and observe about 6 dB of output voltage reduction. There will also be a 180
degree phase inversion at the output of the channel under test.
9

l OUTPUT NOISE
1. Set the amplifier gain controls all the way up, with a I
kHz 1.5OVrms sinewave input
signal. Note the output level at full power just below clipping. Adjust gain if needed.
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 107
dB down
from the full output power point measured. A signal to noise ratio should be better than
or equal to
107dB. 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,
PLX 3002 Test Procedure
l SET-UP
1. Connect a test load to the output terminals of the amplifier.
2. Make sure Mode Switches 1 - 10 are in the default position (1 on, 10 on, all others off).
3. Connect a distortion analyzer with a resolution of O.Ol%, 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:
Chl
- a 1OX (vertical sensitivity - 2V/cm) scope probe to the channel speaker output.
Ch2
- a 1X scope probe (vertical sensitivity - O.lV/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 1.70
VRMS, 1 kHz sine wave.
7. Plug the amplifier into a variac and set up an AC line current monitor.
. POWER UP 8 MUTE DELAY TEST
CAUTION: To avoid damage to the main printed circuit board, place a 50 ohm 225Wresistor (100 ohm,
240VAC) in series with the high
(+) lead on the AC cable during variac ramp up. If the switching power
supply has a shorted device at initial power up, this AC resistor pad will help prevent undue damage. After
the amplifier has been fully powered up via the variac, confirm that the amplifier has achieved
stable operation during idle. Remove AC power from the amplifier and disconnect the series
resistor for normal operation. Continue with the test
& calibration process.
1. Slowly raise the variac voltage and watch for excessive current draw (line current
greater than
0.5A a.c. at 60 Volts). TIG.s is s/ight/y less for 24UV. Pause at 9OVAC
(2UOVAC European) for three seconds until the mute / protect circuit disengages.
Continue to
12OVAC (240V European).,
2. Verify that the fan is operating at low speed.
3. Turn the power switch off and on a few times to verify the 3 second power-up muting
delay.
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 I contaminated gain pots by
observing general instability on the distortion waveform while adjusting the gain control
levels.
10

2. Select an 8 ohm load and confirm that this amplifier is producing 550 watts at 1 kHz just
below the point of clipping. Check both channels.
l BRIDGE MODE
1. Turn the power switch off.
2. Set Mode Switch
#7 in the on position. The gain control, limiter, and filter switch positions
on CH2 are disabled with Mode Switch
# 7 on.
3. Set load to both red output binding posts
(CHI positive and CH2 negative).
4. Apply a 1.30 VRMS, 1 kHz sinewaveinput to channel 1 of the amplifier. Check the power
and verify that the output does not immediately collapse. Check for 2000 watts at 8
ohms.
5. Turn power off and place the amplifier under test back into the Stereo mode with output
loads connected to each channel.
l BIAS
1. Let the amplifier cool down to room temperature.
2. With an input amplitude of 1.7OVrms increase the input frequency to 20kHz. Reduce the
input signal 20dB
(80°h) from full output. Adjust the crossover trimpot VR43 (CHI) and
VRl66 (CH2) 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 so that
the total distortion for that channel is less than 0.1% THD+N.
3, With the trim settings achieved, and 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
amperes.
4. Let the amplifier cool down and check channel 2.
l SHORT CIRCUIT CURRENT
1. Select a 2 ohm load and apply a 1.3Vrms 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, combined AC line current draw for
both channels should be no greater than
13A ac. This is with a 120 volt AC service to
the amplifier. Current may be lower if AC line voltage is lower.
3. Remove the short from each channel and verify that the channels recover in to 2 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.
4. If the amplifier does not pass any of the above steps, troubleshoot the current limit
section of the amplifier. If steps 2, 3, and 4 above pass, continue to the next test
FREQUENCY RESPONSE.
l FREQUENCY RESPONSE
1. Set load to 8 ohms and scale the input generator to gain I watt of power from the
amplifier on each channel. Gain controlson the amplifier should be fully up.
2. Check frequency response from
2OHz to 20kHz (+I- 0.2OdB) by sweeping random
frequencies between these extremes. This is done by verifying the same voltage
amplitude at each of the frequencies selected (within
2OHz to 20kHz). Check both
channels.
11

l POWER vs. DISTORTION TEST
1. Check to ensure that both channels will produce rated power at 2OH2, 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 0.03% THD.
l THERMAL TEST
I. Set input frequency to 1 KHz and short both channels while they are producing power into
a load.
2. Apply a short to the output of each channel.
3. AC line current draw should be about 11
- 13.5 amperes for both channels. As the
amplifier gets hot, there will be some current drift upwards and the fan speed will
increase. This is not a problem as long as the case temperature on the output
transistors does not exceed 105 degrees
C.
4. Verify that the NTC circuit causes thermal shutdown after an extended period.
5. When thermal shutdown occurs, verify AC idle current of less that 0.90 amperes.
l CM TEST
1. Select an 8 ohm load and confirm that this amplifier is producing rated power.
2. Check the Common Mode of the amplifier by inserting a
114” input jack halfway into each
channel and observe about 6 dB of output voltage reduction. There will also be a 180
degree phase inversion at the output of the channel under test.
l OUTPUT NOISE
1. Set the amplifier gain controls all the way up, with a 1
kHz 1.7OVrms sinewave input
signal. Note the output level at full power just below clipping. Adjust gain if needed.
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 107
dB down
from the full output power point measured. A signal to noise ratio should be better than
or equal to
107dB. 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.
12

T r o ubleshooting
PLX 1202 l PLX 1602 l PLX 2402 l PLX 3002
Power Supply - -
Replacing Blown IGBTs.
In order to improve EMI performance, reduce cost, and increase current capacity, the PLX IGBTs
are driven by an active, direct coupled integrated circuit, rather than a gate drive transformer. IGBT or
driver failure should be rare (when correctly assembled) but when the IGBT’s blow, it usually damages the
following parts:
CHECKLIST AFTER BLOWN IGBT’S
Q96, Q97, (IGBT’s generally fail in pairs)
D78, D79, R358, R359, gate drive coupling comonents, check after removing blown IGBT’s.
Ul8, lR2110 high-side gate driver, Fault current when low-side IGBT shorts to upper rail. Such currents
also typically damage the gate coupling parts noted above.
Ul9, 3525 controller, Blows from currents shorted thru Ul8, or possibly by overvoltage on the supply rail
SOMETIMES Ul4, 556, powered from 5V output of 3525, which may fail high when 3525 fails.
RARELY Ul3, which has fairly high supply voltage ratings.
PROBABLE CAUSES OF MASSIVE IGBT FAULTS
SHORTS IN CONTROL CIRCUIT.
The parts operate well within their ratings and should hold up well in the field. The usual cause of failure is
when both IGBT’s turn on at once, shorting Pri-Hi to Pri-Lo. This occurs when something causes the drive
signal to one part to remain on when the other part is supposed to turn on. Shorts from solder or debris are
one obvious cause.
SHORTS IN THE LOAD.
Although there is peak current shutdown, shorts in the power amplifier transistors or secondary-side supply
components can cause currents to increase too quickly to prevent damage.
OVERVOLTAGE ON THE BIAS SUPPLY.
If the TOP-210 bias supply fails to operate, no harm occurs, the unit simply does not operate.
However, open circuit (missing part) in several key components can cause the Bias supply voltage to be
much too high, This blows the 2110 and thus the IGBT’s.
QUICK TEST OF BIAS SUPPLY.
Ramp the AC voltage up slowly to 25% of regular voltage (30V for 12OV unit). If the bias supply is working
normally, the green “power” LED should come on between 30 and 35Vz with its usual, steady “half-brighr
start-up level. If the LED comes on at 2OV, or not until 5OV, or blinks, DO NOT RAISE VOLTAGE PAST 60V
until you have measured the bias voltage. The switching will not start until you reach 9OV, so you can save
the IGBT’s from blowing.
Confirm that bias voltage at Cl38 is 18-19V. Open or missing D63, 64, 65, 66, 67 or R349 will break the
feedback to U16 and cause overvoltage.
13

Troubleshooting “TOP-210” Bias Supply.
QUICK TEST OF BIAS SUPPLY.
Ramp the AC voltage up slowly to 25% of regular voltage (30V for 12OV unit). If the bias supply is working
normally, the green “power” LED should come on between 30 and 35V, with its usual, steady “half-brighf’
start-up level.
CAUTION: if the LED comes on at 2OV, or not until 5OV, or blinks, DO NOT RAISE VOLTAGE PAST 60V
until you have measured the bias voltage. The switching will not start until you reach 9OV, so you can save
the IGBT’s from blowing.
Confirm that bias voltage at Cl38 is 18-19V.
BIAS SUPPLY VOLTAGE MUCH TOO HIGH
D63,64,65,66,67 or R349 open or missing -- breaks feedback to U16
NO BIAS SUPPLY VOLTAGE
U16 missing or blown.
Tl missing, reversed, or open primary
D62 open or missing.
BIAS VOLTAGE ERRORS
The exact voltage is controlled by the feedback through D63, 64_ 65, 66, 67 and R349 as follows:
Cl38 is the “+18V’ rail with about 18.8V typical.
D63, 64, 65 each subtract a diode drop (0.7V) from Cl38.
Cl39 , is the “+16V” rail with about 16.6V typcial.
D66, a IOV zener diode , plus diode D67, subtract about 1 IV from +16.6V.
R349 subtracts about 0.5V, bringing the net voltage at Ul6, feedback pin 4, to about 5.lV.
Ul6 uses this feedback to adjust the “on” time at pin 5, in order toraise or lower the flyback voltage
charging Cl38 and thus maintain regulation of the +16V and +18V supplies
C142, R356, and R349 form a closed-loop stability circuit which prevents the regulated voltage from
“hunting”.
Q99 and associated R374 reduce the voltage of the Bias supply by 33% when the AC voltage is turned off.
This prevents the Power LED from showing at half brightness after turn-off, since U16 continues to run
from the main filters for some time after shut down R375 and 376 sense the output of Ul3:3, the “Loss of
AC” comparator, and cause Q99 to turn on. If Q99 is shorted, the bias voltages will remain 33% low when
AC is turned on.
REPLACING BLOWN TOP-210.
If U16 has blown, check T-l for continuity after removing Ul6. Its primary may be open. Pins I-2 It should
measure about 15 ohms
Replacing Blown Output Transistors
OUTPUT TRANSISTOR SHORTED
Stmrk in one device tend to cause the opposing device to blow as well,
If an output transistor shorts:
Drive transistor will be shorted (Q26, Q27, Q71, Q72)
CXNne transistors will short in pairs (Q39 & Q40, Q36 & Q37, Q84 8 Q85, Q81 8, Q82)
The rest will short in fours (Q28, Q29, Q34 & Q35; Q73, Q74, Q79 8, Q80)
IGBT’s 8 their associated components may fail
14

CHECK EMITTER AND BASE RESISTORS WHILE DEVICES ARE REMOVED,
Each output transistor has an associatated pair of 0.47 ohm resistors in parallel.
Each BANK of output transistors has a 15 ohm resistor from base to rail (emitter bus).
Audio Outputs, Troubleshooting Current Limit
WEAK CURRENT LIMIT -- PREMATURE CLIPPING.
The usual symptom of weak output current is premature clipping of one or more peaks of the audio voltage.
This could be caused by missing step, weak current limit, or dead output section.
PREMATURE CLIPPING at 60% VOLTAGE, SIMILAR AT ALL IMPEDANCES:
This points to a step problem (2402, 3002 only). See Step Troubleshooting.
If the amplifier reaches full voltage at 8 ohms, but prematurely clips at 4 ohms or 2 ohms, we can assume
the step is OK but the output current is too low (see below).
NO OUTPUT AT ALL ON ONE POLARITY.
This indicates complete failure (open circuit) in the circuit leading to the dead output polarity. Check the
series components in the current splitter for missing or open:
Ch 1:
Positive, Ql9, R381, Q20, R70, DIO, D14. Negative: Q22, R382, Q21, R71, Dl I, D12
Ch 2:
Positive, Q64, R383, Q65, Rl93, D35, D39. Negative: Q67, R384, Q66, Rl94, D36, D37
CONSTANT, PREMATURE CLIPPING, WORSE AT LOW IMPEDANCES.
First, check the clamping voltages on C21 (Ch I+), C22 (Ch I-), C56 (Ch 2+), C57 (Ch 2-), as shown in
table below. At idle, all four voltages should all be similar. If one is out, check parts according to the
following table
CLAMPING VOLTAGES ARE WRONG AT IDLE
CHANNEL-POLARITY
Measure voltage on:
3002 and 2402, about 6V.
1602, about 4,6V,
1202 about 4.9V.
Voltage too high: missing resistor:
or missing transistor:
Voltage 0-0.3V: shorted transistor
or missing resistor
Voltage 0.7V, missing resistor:
Voltage wrong: wrong value
CH
I+
CH l-
c21 c22
R60
Q14
Ql4,24
R 51, 72
R59
R59,60
R61
Ql5
Ql5, 25
R53, 75
R62
R62,61
CH
2+
C56
RI83
Q59
Q59,69
Rl74, 195
RI82
Rl82, 183
CH
2-
c57
RI84
Q60
Q60,70
Rl76, 198
RI85
Rl85,184
The exact voltage varies with temperature. Look for the mismatching value on the weak cell.
A too-low voltage causes early clamping of that output section, as explained in the previous several pages.
If the voltage is correct and current is still low, also check for missing - unsoldered output device, or emitter
resistors.
15

Audio Power Stage, Current Limit Troubleshooting
CURRENT LIMITS WHICH COLLAPSE PREMATURELY.
An immediate collapse of ALL current limits at full power could be premature triggering of “Power Supply
Cutback”, which is described in the section below. Cutback after several seconds of full power operation at
two ohms is normal.
Cutback of one or more output sections, at full temperature, while approaching full power into two ohms is
also normal. However, cutbacks at 4 ohms, or when cold into two ohms, indicate problems with the
transistor power measuring circuitry.
CLAMPING VOLTAGES COLLAPSE TOO SOON.
CHANNEL-POLARITY CH
I+ CH l- CH 2+ CH 2-
Measure voltage on:
c21 c22
C56
c57
Cuts back too easily: low value, R67, 73 R68, 74 Rl90, 196 Rl91, 197
or high value: R 51, 72 R53, 75 Rl74, 195 Rl76, 198
or missing diode: D9
D8
D34 D33
CLAMPING VOLTAGES ARE CORRECT, CURRENT STILL WEAK.
Shorted diode DIO, 14
Dll, 12
D35, 39 D36, 37
Missing-unsoldered output device or emitter resistor.
TROUBLESHOOTING “POWER SUPPLY CUTBACK”.
As noted in the section on Power Supply, the amplifier’s current limit cuts back when necessary to protect
the power supply. Because the Observed effect is a reduced output voltage, in response to prolonged
operation above the long-term current limit, we commonly refer to this behavior as “power supply cutback”,
but we must remember that it is actually amp/Tier current hmifhg in response to an overload signal sent
from the power supply. Full power operation into 2 ohms (both channels) should produce a 50% cutback of
current after several seconds.
If both channels of the amplifier fail to cut back after about 3 seconds, 2-ohms, both channels driven, the
cutback signal is probably missing. CAUTION: Prolonged operation under these conditions could blow
IGBT or burn out Cl44. Test for 6-10 seconds maximum.
Check the output (secondary side) pins of U17 (sh 4). Confirm presence of +6V on pin 5. Pin 4 should
normally be at about OV, and go high (I-5V) after 3 seconds at full power,
If
Ul7-pin 4 does not go high, check U17 itself. If it appears OK, trace the circuitry driving U17 (PRIMARY
SIDE, CAUTION). Check for continuity through L6:2 to Pri-Lo, check missing or open R343, D61, Q95,
R347, all of which drive optocoupler U17. A short in R346 or Cl31 will also prevent drive to U17.
If Ul7-pin 4 goes high on schedule, and BOTH channels fail to cut back, trace voltage on “PS_OL” bus to
R273 (sh 3), which connects to “MUTE+” bus. Continue tracing voltage on MUTE+ to Ql6 (sh I) and Q61
(sh 2). If only ONE channel fails to cut back, look for missing Ql6, R 65, Ql7 (sh I) or Q61, Rl88, Q62
(sh 2).
Cl31 controls the speed of cutback.. If missing, the amplifier current limits will enter cutback almost
immediately at or above full power, 4 ohms.
SHORT CIRCUIT CURRENT DOESN’T CUT BACK.
CAUTION: DO NOT MAINTAIN A SHORTED LOAD IF CUTBACK FAILS TO OCCUR WITHIN 1 SECOND.
It will be necessary to measure the output current with a DC current probe, or by noting the voltage across
a low value resistance with a DC scope, in order to determine which output cell is failing to cut back.
Failure to cut back could indicate either lack of clamping, or lack of voltage cutback. Measure the voltage
on the respective clamp capacitor. If the voltage decreases, but current limiting does not cut back, check
the clamping transistor. :
16