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Technical Service Manual
PLXTM Series
v PLX 1202
v PLX 1602
v PLX 2402
v 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: 1-714-754-6173
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 ................................................................ 1
Introduction ........................................................................................ 2
Test and Calibration ............................................................................ 3
Troubleshooting PLX ........................................................................... 13
PLX Parts List
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
PLX Semiconductors .............................................................................. 50
Chassis Drawings ................................................................................... 53
Schematics
PLX 1202 Main PCB Schematics ..................................................... 57
PLX 1602 Main PCB Schematics ..................................................... 62
PLX 2402 Main PCB Schematics ..................................................... 67
PLX 3002 Main PCB Schematics ..................................................... 72
PLX Series PCB Circut Board Drawings ................................................. 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 both channels driven:
8 ohms, 2OHz - 2OkHz, 0.03% T H D 200 watts 300 waKs 425 watts 550 watts
4 ohms, 2OHz - 2OkHz, 0.05% T H D 325 watts 500 watts 700 watts 900 watts
Con0nuous Average Output Power bridged mono ooeration:
8 ohms, 2OHz - 2OkHz, 0.1% THD 700 iatts 1100 watts 1500 watts 2000 watts
Voltage Gain (dB) 32 32 32 32
Sensitivity (for rated power @ 8 ohms) 1.00vrms 1.20 Vrms 1.50 Vrms 1.70 vrms
Distortion SMPTE-IM Less than 0.01%
Frequency Response (LF Switched Off) 2OHz to 2OkHz, +I-0.2dB
8Hz to 5OkHz, +Ol-3dB
Damping Factor (1 kHz and Below) Greater than 500
Noise 106dB below rated output (20 Hz to 20 kHz)
Input Impedance 6k unbalanced, 12k balanced
Dimensions
FaceplateWidth Standard 19" Rack Mounting
FaceplateHeight 3.Y 3.r 3.5" 3.Y
Chassis Depth 13.2Y 13.2v 13.2Y 13.2Y
Weight
Net, Lbs/kg 2119.5 2119.5 2119.5 2119.5
I n t r o d u c t i o n
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 CAUTION
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 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 -Audio Precision - System One
- High Power Load Bank (8,4,8 2 ohms) + Thermometer
- Function Generator 8 Digital Multimeter
- 2OMHz Oscilloscope
- Variac (0-140 VAC, 30-40A)
2
T e s t & C a l i b r a t i o n
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 sinewave input 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 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
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. 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 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.
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.
l 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.
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 sinewave input 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 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). 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 sinewave input 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