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Technical Service Manual
PLXTM Series
v v v v 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: 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 ................................................................ Introduction ........................................................................................ Test and Calibration ............................................................................ Troubleshooting PLX ........................................................................... PLX Parts List
PLX 1202 PCB Assembly (120V) ..................................................... PLX 1202 PCB Assembly (230V) ..................................................... PLX 1202 Chassis Assembly (120V) ................................................ PLX 1202 Chassis Assembly (230V) ................................................ PLX 1602 PCB Assembly (120V) ..................................................... PLX 1602 PCB Assembly (230V) ..................................................... PLX 1602 Chassis Assembly (120V) ................................................ PLX 1602 Chassis Assembly (230V) ................................................ PLX 2402 PCB Assembly (120V) ..................................................... PLX 2402 PCB Assembly (230V) ..................................................... PLX 2402 Chassis Assembly (120V) ................................................ PLX 2402 Chassis Assembly (230V) ................................................ PLX 3002 PCB Assembly (120V) ..................................................... PLX 3002 PCB Assembly (230V) ..................................................... PLX 3002 Chassis Assembly (120V) ................................................ PLX 3002 Chassis Assembly (230V) ................................................ 23 25 28 28 28 31 34 34 35 38 41 41 42 45 48 49 50 53 57 62 67 72 73 1 2 3 13
PLX Semiconductors .............................................................................. Chassis Drawings ................................................................................... Schematics
PLX 1202 Main PCB Schematics ..................................................... PLX 1602 Main PCB Schematics ..................................................... PLX 2402 Main PCB Schematics ..................................................... PLX 3002 Main PCB Schematics .....................................................
PLX Series PCB Circut Board Drawings .................................................
PLX Product Specifications
PLX 1202
PLX 1602
PLX 2402
PLX 3002
PLXI 202
PLXI 602
PLX2402
PLX3002
550 watts 900 watts 2000 watts 32 1.70 vrms
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 4 ohms, 2OHz - 2OkHz, 0.05% T H D 325 watts 500 watts 700 watts Con0nuous Average Output Power bridged mono ooeration: 8 ohms, 2OHz - 2OkHz, 0.1% THD 700 iatts 1100 watts 1500 watts Voltage Gain (dB) 32 32 32 1.00vrms 1.20 Vrms 1.50 Vrms Sensitivity (for rated power @ 8 ohms) Distortion SMPTE-IM Less than 0.01% 2OHz to 2OkHz, +I-0.2dB Frequency Response (LF Switched Off) 8Hz to 5OkHz, +Ol-3dB Damping Factor (1 kHz and Below) Greater than 500 Noise 106dB below rated output (20 Hz to 20 kHz) 6k unbalanced, 12k balanced Input Impedance Dimensions FaceplateWidth Standard 19" Rack Mounting FaceplateHeight 3.Y 3.r 3.5" Chassis Depth 13.2Y 13.2v 13.2Y Weight 2119.5 2119.5 Net, Lbs/kg 2119.5
3.Y 13.2Y 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 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
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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.
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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. 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.
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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.
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FREQUENCY RESPONSE 1, Set load to 8 ohms and scale the input generator to gain 1 watt of power from the amplifier on each channel. Gain controls on the amplifier should be fully up. 2. Check frequency response from 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. 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. 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.
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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
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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. 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. 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.
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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. 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.
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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.
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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. 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.
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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. 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. 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.
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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. 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. 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.
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PLX 2402 Test Procedure
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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. 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.
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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.
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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. 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. 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
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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.
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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. 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. 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. 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.
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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.
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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. 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,
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PLX 3002 Test Procedure
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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.
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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.
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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.
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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. 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.
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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. 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.
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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. 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. CM T E S T 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. 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. 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.
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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
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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+ c21 CH lc22 CH 2+ C56 CH 2c57
R60 Q14 Ql4,24 R 51, 72 R59 R59,60
R61 Ql5 Ql5, 25 R53, 75 R62 R62,61
RI83 Q59 Q59,69 Rl74, 195 RI82 Rl82, 183
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.
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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 Measure voltage on: Cuts back too easily: low value, or high value: or missing diode: CH I+ c21 R67, 73 R 51, 72 D9 CH lc22 R68, 74 R53, 75 D8 CH 2+ C56 Rl90, 196 Rl74, 195 D34 CH 2c57 Rl91, 197 Rl76, 198 D33
CLAMPING VOLTAGES ARE CORRECT, CURRENT STILL WEAK. Dll, 12 Shorted diode DIO, 14 Missing-unsoldered output device or emitter resistor.
D35, 39
D36, 37
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. :
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CLAMPING VOLTAGE DECREASES, BUT NO CURRENT CUTBACK CHANNEL-POLARITY Measure voltage on: Check clamp transistor CH I+ c21 Q18 CH lc22 Q23 CH 2+ C56 Q63 CH 2C5? Q68
If the measured voltage on the clamp capacitor is not decreasing to about 50% during the short, check the circuitry which measures the current during short circuit, CLAMPING VOLTAGE DOES NOT DECREASE TO 50% DURING SHORT. CH I+ CHANNEL-POLARITY Measure voltage on: c21 Missing cutback transistor, resistor Q24, R67 Missing voltage sense resistor, R 73 Shorted or low value shunt resistor R72 CH lc22 Q25, R68 R 74 R75 CH 2+ C56 Q69, RI90 RI96 RI95 CH 2c57 Q70, RI91 RI97 RI98
Troubleshooting Thermal Tracking
MOUNTING PROBLEMS WITH IOK SENSING NTC. The thermal sensing for fan and bias tracking depends on a 1 OK NTC which is mounted in a hole in the heat sink. The hole is filled with thermal grease to improve coupling. If the NTC is not straight while mounting the heat sink, it may short out against the side of its hole. It is mounted on a standoff which protrudes into the hole, so this should not occur if care is taken while installing the heatsink. If shorted to the heat sink, the amplifier output voltage is coupled to the NTC. If the short is to the grounded lead of the NTC, it may not damage anything. If to the other end, a large voltage is put across the NTC which will probably damage it. SHORT FROM "LIVE" END OF NTC TO HEAT SINK: Replace affected NTC BE AWARE! This can short (relatively) quietly and then appear to be operating normally. Poor bias tracking can indicate this problem. Sometimes this short will not happen until the amplifier is driven past IV input. NTC BENT OVER AND SHORTED TO DRIVER TRANSISTORS. May touch Ql9, Q26, or Q64, Q71. This causes severe overcurrent to the affected output cell, possibly damaging the parts in series with the shorted transistor. It may also blow the power supply. Replace affected NTC, drive transistors, check components in series with drive transistor Ch 1: Ql9 shorted, check, R381, Q20, R70, DIO, D14. Q26 shorted, check ALL outputs and opposing driver transistor on this channel. Ch 2: Q64 shorted, check R383, Q65, Rl93, D35, D39. Q71 shorted, check ALL outputs and opposing driver transistor on this channel.
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Audio Output, Troubleshooting Stability Feedback
HIGH FREQUENCY OSCILLATIONS SEVERE-DRAWS CURRENT-GROSS DISTORTION C27 (62) missing or wrong, or series R367 (368) C 25, 26 (60, 61) missing Secondary filter capacitors missing or open (unlikely that ALL are defective). SEVERE, BUT DOES NOT DRAW LARGE CURRENT R22 (146) open. MARGINAL -- MAY APPEAR ONLY AS EXCESS DISTORTION Cl4 (49) missing Cl 6 (50) missing or too large C28 (63) missing C 25 or 26 (60 or 61) missing or too large Cl95 or 196 missing (input board). EXCESSIVE OSCILLATION JUST BELOW CLIPPING, 2-4 ohms Cl 7 (52) missing NOTE: about 0.1% oscillation right below clipping at 2 ohms is normal. EXCESSIVE SWITCHING INTERFERENCE. Switching interference may LOOK like an instability, however it is at a much lower frequency (1lOkH.z) than most instabilities. It will be more visible at low frequencies (2OOHz) and at lower impedances. Missing jumper at R224. Missing Cl29, 134 on output board. Grounds not connected to chassis at output board and front chassis mounting screw.
FEEDBACK PROBLEMS: GAIN INCORRECT Gain of output stage set by R23, 31 (147, 153) Gain of Ch 1 volume control buffer stage set by RI 1, 16. Gain of Ch 2 volume control buffer stage set by Rl37, 139. Make sure Q48 is turned on - grounding RI37 at Q48 should not affect gain. Check RI 32 (drives Q48). Gain of balanced input is set by 4 matched resistors R9, 8, 12, 13 (129, 130, 135, 136). Confirm both sides of balanced input are working. Check R5, 6 (123, 124).
Audio Output, Troubleshooting Clipping, Limiting
EXCESS STICKING (TOO MUCH DISTORTION DURING CLIP LIMITING) Cl4 (49) much too large (also causes increased high frequency distortion). R38 (161) missing. R38-39 (161-162) have wrong values. Q9, 10 (54, 55) missing R34 (157) or R35 (158) missing Q8 (53) missing
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CLIP LIMITING DOESN'T WORK: BOTH CHANNELS: Check U3 missing, Check U3 supply voltages, +I 3VCL, -13VCL, on C73* 74 ONLY ONE CHANNEL BAD: Probe output of U2 (7), pin 7 while clipping. If output exceeds 4V during clipping, check : R38 (161) missing. R38-39 (161-162) have wrong values. Q9, 10 (54, 55) missing. R34 (157) or R35 (158) missing Q8 (53) missing If output at pin 7 clamps at 3.5.4V as expected, check parts surrounding U3: R32 (154) missing Q7 (52) missing R28 (151) missing Q6 (51) missing RI8 (141) missing RI9 (142) missing SW I:1 (1:lO) not making contact Check each pin on U3 CLIP LIMITING OSCILLATES: Cl 3 (48) missing. R21, 27 (144, 150) missing
Troubleshooting Step Problems
EXCESSIVE STEP DISTORTION (STEP GLITCH) Close scrutiny of the distortion trace, and scope probing of the switched waveform, will help determine the cause of excess step distortion, The step should switch when the output voltage is within IO-12 volts of its respective rail, This switching margin should be fairly constant from 20- 20kHz. The switching event itself should be a fairly uniform up and down ramp, moving at about 25 volts/us, therefore taking about 2us to complete its transition. Step Switching Too Close to the Rail: This will cause increased step glitch, especially at low impedances. If present at all frequencies, check the reference voltages: Negref: 17.5 volts above its intermediate rail: D88, R276-7-8. PosRef: 20V below its intermediate rails: D87, R256, 257, D53.
Confirm correct values in output voltage divider: R48 loaded by R49-50 (Rl71, and Rl72-173). If present only at high frequencies, check the value of the speed up capacitor C20 (C55) in the output voltage divider, or look for slow switching (see below).
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Step Chattering. If the step repeatedly switches on and off, usually at a low frequency, it creates an oscillation burst which increases step glitch at low frequency. The tendency is usually worse at low impedances and low frequencies. 2-3 "false trials" at very low frequency, 2 ohms, is normal, but prolonged bursts of maximum frequency chattering may cause FET failure. Positive step: check hysteresis resistor R66 (RI 89) Negative step: check hysteresis resistor R69 (RI 92) and capacitor Cl 87 (Cl 93). Slow or Fast Switching. Slow switching reduces step glitch but puts more strain on the FET. Fast switching increases step glitch. The usable limit is 17-27 volts/us, If both slopes are equally off speed, check the slope capacitors: Positive, C30 (C65) and Negative, C29 (C64). If only one slope is slow, check the resistors and buffer transistors: Positive step: R78, 79, Dl5, Q30-31 (R201, 202, D40, Q7576) Negative step: R83, 84, Dl7, Q32-33 (R206, 207, D42, Q77-78). Step FET Oscillation. Certain FET types oscillate at extremely high frequency while ramping up and down. This injects interference into the amplifier which increases the step glitch. Such problems are supposed to be found while (dis)qualifying specific FET types. If they crop up in production, Engineering needs to know. STEP WON'T TURN ON (Premature Clipping) If the step refuses to switch high, the amp will clip prematurely, at the intermediate rail, at any load. Make sure the clipping is not acually current cutback, usually evident only at 2 ohms. Probe the output voltage and intermediate rail voltages to confirm clip point and lack of step action. Trace the circuit from the step FET back via gate drive to drive circuit to locate cracks, missing part etc. Check DC power on step driver (14V on EACH positive step drivers, 12V on BOTH negative drivers). Check voltage of PosRef (20V below +65V rail) or Negref (17.5V above -65V rail). Look for severe mismatches of the comparator resistor ladders. STEP STUCK ON (Switched Rail Voltage Stuck On Full) If the positive step is stuck on, (evidenced by permanent high voltage on switched rail) the FET is probably bad, since the positive gate drive cannot sustain DC turn-on due to the bootstrapping. If the negative step is stuck on, it could be a bad FET, or the gate drive circuit could be holding the FET on, which will easily be confirmed by measuring the gate voltage. Malfunctioning gate drive circuitry should be checked as noted above under "Won't Turn On". REPEATED FET FAILURE. Repeated failure of step FET's is usually caused by failure to fully switch ON or OFF (lingering in the linear region). The actual failure usually occurs at 2 ohms, where the dissipation is highest. After replacing the FET, the step waveform should be monitored, starting at light load to avoid repeated failure, and advancing briefly to heavier loads while closely watching the waveform. You will need to use an isolated scope probe which allows voltage readings to be taken with respect to the intermediate rails, or to FET sources. FET Does Not Fully Turn On: Generally causes problems at low frequency, 2 ohms. Confirm that the step FET remains fully on for the entire cycle (2OHz). If not, confirm weak gate drive and determine cause. Weak positive drive: check voltage on C32 (C51) for 14V. Check C31 (C66), low RIO4 (R227), missing D18 (Dl48). Check R78, Dl5, Q30 (R201, D40, Q75). Weak negative drive: check voltage on C67, 12V. Check R83, Dl7, Q32 (R206, D42, Q77).
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FET Turns On or Off Very Slowly: Generally causes problems at high frequency, 2 ohms. If both slopes are equally slow, check the slope capacitors: Positive, C30 (035) and Negative, C29 (034). If only one slope is slow, check the resistors and buffer transistors: Positive step: R78, 79, Dl5, Q30-31 (R201, 202, D40, Q75-76) Negative step: R83, 84, Dl7, Q32-33 (R206, 207, D42, Q77-78). Severe Step Oscillation. Generally observed at low frequency, low impedance, right at threshold. Positive step: check hysteresis resistor R66 (RI 89) Negative step: check hysteresis resistor R69 (RI 92) and capacitor Cl 87 (Cl 93)
Troubleshooting DC Fault Shutdown
NORMAL BEHAVIOR OF THE CIRCUIT. Any amplifier fault which causes a non-symmetrical output, such as premature clipping of one polarity, a missing step, etc, may trigger DC fault shutdown. This indicates normal operation of the circuit TRACING THE CAUSE OF FALSE TRIGGERS. If amplifier is shutting down for no apparent cause, the source of the false signal must be found. Be sure the output is checked with a DC coupled scope in order to confirm absence of an actual DC offset. The circuit will trip on DC offsets exceeding about 4V. The optocoupler's input can be safely disabled by shorted Ul5, pins I-2 together. This will indicate if false triggering is before or after Ul5. The output of UlO:l, pin 1 should be monitored. If it goes low during DC shutdown, it is sending the false signal. SHUTDOWN OCCURS AS SOON AS SWITCHING STARTS. Disable Ul5 as noted above, determine if there is a DC fault condition. CAUTION: use 50-ohm resistor in series with AC line to limit fault current in case of shorted outputs. If amplifier output looks OK, check UlO:l output. If low, check voltage on pins 2 and 3 UlO:l, pin 2: should be zero (no signal) UlO:l, pin 31 should be about 2V! set by R243, 244, 245. Check R348 at Ul.5. SHUTDOWN OCCURS ABOVE ABOUT 4V OUTPUT: Q87, C7, R240 or D48 missing. Confirm D48 is pulled low (-13V), holding Q87 on. If not, check RI 17, 118, Q42 NOTE: this control voltage responds to the Br Mono switch, pole 7. Check R348 at Ul5. Bad connection at step diodes (D21, D22, D46, D47)
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Fan Speed Troubleshooting
FAN STUCK HIGH: Q88 or Q89 failed R30 or Rl55, Thermal Sense NTC, shorted to heatsink R266 or R271 missing. FAN DOESN'T RUN Check fan voltage, should be 1 IV when cold, 29V when hot. Voltage OK -- replace fan. No Voltage: check Q91, 89, 90, R264 and 265 missing. Confirm that +/-15V is reaching circuit.
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PLX 1202 PCB ASSEMBLY (12OV)
Part Number Description Reference
PLX 1202 PCB ASSEMBLY (12OV) Cont'd
Part Number Description Reference
c14,49 CA-01 0002-30 CAP 1 OPF 5% 50V 0805 SMT Cl6,50 CA-01 5002-10 CAP CER 15PF 10% 5OOV SL CA-I 10002-30 CAP CER 1 OOPF 5% 5OV NPO SM C40,41,43, C5,6,9,18, c53 Cl45,146 CA-I 33001-10 CAP SM 330PF 5% 500V CA-I 47003-30 CAP 470PF 5% 5OV 1206 SMT Cl,2,4,17, c119,121, Cl48,181, Cl82,186, Cl88 C26,36,37, C52,61, CA-168003-30 CAP CER 68OPF 5% 5OV NPO SM C25,60 CA-21 0005-30 CAP ,001 LJF 5% 5OV 1206 SMT Cl20,124, Cl95,196 C75,81,85, CA-222001-00 CAP CER Y .0022UF 20% 125VAC Cl22,127 CA-227001-30 CAP CER .0027UF 10% IOOV 0805 ClO8,109, Cl28 C20,23,24, C55,58,59, CA-233001-10 CAP MYLAR .0033UF 10% IOOV Cl13 CA-233002-00 CAP CER Y .0033UF 20% 125VAC Cl 15,118 CA-322001-10 CAP MYLAR .022UF 10% IOOV C27,62 CA-410001-00 CAP MET POLY X.lUF 20% 250V Cl26 CA-410002-10 CAP MYLAR .lUF 5% IOOV c47 C8,12,44, CA-410003-10 CAP MET POLY .lUF 10% 250V Cl29,134, Cl56,157 C28,63, CA-410006-30 CAP CER .lUF 10% 5OVX7R SMT Cll6,125, c135,155, Cl62,163, Cl79,180, Cl83,185, Cl89,190, c19,39,54, Cl91 ClO7,123 CA-410011-00 CAP MMYL .lUF 10% 400V CA-422001-10 CAP MYLAR .22UF 5% 5OV c10,45 CA-447001 -00 CAP MET POLY X.47UF 20% 250 Cl 17 Cl44 CA-447003-00 CAP POLYP .47UF 10% 400V Cl3,48,184 CA-51 0005-30 CAP LYTIC 1 UF 20% 5OV SMT CA-510006-00 CAP MPOLY X IUF 20% 25OVAC Cl 10,112 CA-61 0002-10 1 OUF,35V,2O%,RADlAL ELECT Cl92 C3,38,80, C86,114, CA-647001 -10 CAP LYTIC RL 47UF 10% 1 OV NP C46,71 C7,11~42~ CA-647002-1 0 CAP LYTIC RL 47UF 20% 5OV C21,22,56, C57,89 CA-71 0002-10 CAP LYTIC RL 1 OOUF 20% 25V c139,142, Cl43 Cl5*33,72! C78,79, CA-71 0004-10 CAP LYTIC RL IOOUF 20% 25V Cl38,149, Cl50 CA-747001 -10 CAP LYTIC RL 47OUF 20% 16V C73374>763 c77,131 CA-747004-00 CAP LYTIC RL 47OUF 20% 1OOV Cl52,153, Cl59,160,
Cl65,166, Cl69,170 CA-822200-AE CAP LYTIC RL 22OOUF 20% 200V Cl 32,133 CH-000102-00 HEATSINK, AUDIO, PLX CH-000103-00 SPRING, CLAMP, 2 HOLE CH-000104-00 HEATSINK PS PLX CH-0001 1 I-00 BRACKT,OUTPUT PCB PLC PLATFORM CH-000114-00 CLAMP, 2 FINGER PLX CO-000036-CO SPEAKONS, PC MOUNT J7,8 CO-000148-00 CONN XLR F VERT PCB J2,lO CO-000155-00 HEADER PCB ,100 2-POSITION J13 CO-000162-00 BNDG POST A, DUAL SLOT, PLX CO-000163-00 BNDG POST B, DUAL SLOT, PLX CO-3001 12-PJ JACK 1/4" PHONE DBLOPEN CKT Jl,9 REF: Fl HW-OOOOOI-FC FUSE CLIPS IC-000024-00 IC REG PWM 40V O.lA SG3525A Ul9 IC-000047-30 IC LIN DUAL COMP LM393 SO-8 UIO Ul,6 IC-000048-30 IC LIN DUAL OP AMP MC33078 IC-000051-00 IC OPTO-IS0 MOC8101 u1517 IC-000053-30 IC LIN SMT DUAL TIMER LM556 Ul4 IC-000054-30 IC LIN SMT QUAD COMP LM339A Ul3 IC-000073-30 IC LIN DUAL OP AMP LMI 3600 U3 IC-000134-00 IC CMOS HV DRVR lR2110 Ul8 IC-000135-00 IC LIN PWM SWITCH TOP 210 Ul6 IC-005532-OP IC LIN DUAL OP AMP 5532 EXIMP U2,7 REF: Q91 MS-000048-HS HEAT SINK, ISOL TO-220 MS-0001 12-00 FUSE 25A 125V 3AG FAST CER Fl PC-000531-00 PCB MAIN PLX PL-000114-00 INSUIATOR, IGBTIRECT HS, PLX PL-000726-00 SPRING, SEAT, PLX LD2-LDI 1 PL-000128-00 SPACER, LED, ,276" REl55,LDl, REF:R30, PL-000135-00 INSULATOR, MICA 1.25" X 1.75" REF:Q96,97 PL-905156-SP SPACER,ROUND,NYLON,#6,0.155 REF:Ll,2 PT-125000-AT RES VAR IT 250 20% 0.15W CAR VR43,166 PT-310000-CR RES VAR IT IOK 20% 0.2W W/DE VR2,121 QD-000014-QD DIODE TO220 ULTRAFAST 200V D74,75,80, D81 QD-000042-00 DIODE RECT ULTRAFAST 400V 3 D70,71 LD2,3,4,7, QD-000052-00 LED GRN T-l LD8,9,11 LDI ,6 QD-000053-00 LED YEL T-l QD-000054-00 LED RED T-l LD5,lO QD-000062-10 XISTOR NPN TO-92 40V 0.2A 1.5 Q20,65 QD-000063-10 XISTOR PNP TO-92 40V 0.2A 1.5 Q21,66 Q27,72 QD-000076-00 XISTOR NPN TO-220 250V Q26,71 QD-000077-00 XISTOR PNP TO-220 25OV QD-000102-30 DIODE SW IN4148 SMT 75V 75M Dl-5,8,9, DIO-12,14, D23-30,33, D34-37?39_ D48-51,55, D59,63, D64,65,67, D69,89,90, D91 Ql3,15;18, QD-000103-30 XISTOR NPN SMT 40V .2A .2W Q25,49,50,
Q5,7,&%
Q52?53,54? Q58,60,63, 23
PLX 1202 PCB ASSEMBLY (12OV) Cont'd
Part Number Description Reference
PLX 1202 PCB ASSEMBLY (12OV) Cont'd
Part Number Description Reference R21,27,70, R364,381, R382-384 R71,144? RI 91,204, R205 R67,68,81, R82,190, R44,167 R256,257, R27632773 R278 Rl51,160 R283377 R22,146, R361_374 R370 RI 37,423 Rll7,118, Rl28,165, R232,250, R252,369 RlOl,lO9, Rl47,154, Rl57,158, Rl62,164, R23,32334, R270,273 R35,39,41, Rl27,171, Rl95,198 R48s72_753 R240,264, R265,267, R3473348 R47,170_ R251 Rll,l7, Rl25,126, Rl31,137, RI 3a1253v R3,4,10, R327_3307 R362 Rl3,129, Rl30,135, RI36 R8,9,12, Rl22,152, Rl82,185 R29,59,62, Rl20,132, Rl40,161 RI 5,38, R360 R258,266, R272 R36,159, R336,338v R363,366, R375,376 RlO6,133,
Q70,89,90, Q92,93,95 Ql-4,6,10, QD-000104-30 XISTOR PNP SMT 40V .2A .2W Ql2,14,23, Q24>42143, Q44-48,51, Q55,57,59, Q68,69,87, Q88,94,98, Q99 QD-000105-30 XISTOR NPN SMT 300V .2A .2W Ql6,61 QD-000106-30 XISTOR PNP SMT 300V .2A .2W Ql7,62 QD-000108-30 DIODE SMT SWITCH 200V .2A 50 Dl3,16,38, D41,61,68, D78,79 QD-0001 lo-30 DIODE ZNR 6.2V 5% .3W SMT D56 QD-000113-30 DIODE ZNR IOV 5% .3W SMT D66 D58,60,86 QD-00011530 DIODE SMT RECT 600V IA QD-000116-30 DIODE RECT SMT 200V IA D62*76,77j D82,83 QD-000154-00 XISTOR NPN TO-220 230V Ql9,64 Q22,67 QD-000155-00 XISTOR PNP TO-220 230V QD-000156-00 XISTOR PNP TO-220 1OOV 3A 40 Q91 QD-000162-00 XlSTOR,lGBT 2OAI6OOV Q96,97 QD-000170-00 DIODE BRIDGE RECT 600V 5OA BRI QD-001302-PN XISTOR PNP TO-3P 200V 15A Q28,36,39, Q73181,84 QD-003281-NP XISTOR NPN TO-3P 200V 15A Q29,37,40, Q74,82va5 QD-004744.ZA DIODE ZNR 15V 5% 1 W 1 N4744A D53,54 Dl9,20,44, QD-005402-DX DIODE RECT DO27 200V 3A D45 RE-.04703-10 RES MOFP .47 5% 2W MINI RlO3,107, R108,111, RI 12-114, R211,212, R214,215, R225,226, R230,231, R234-237 Raasa9,91 ~ R92,102, R203,221, RE- 56002-10 RES MOFP 5.6 5% 2W MINI R354,355, R373 R80,98, RE-000210-NR THERMISTOR NTC 15A CUR LIM R324 RE-000230-NR THERMISTOR NTC IOK 5% R30,155 RE-001003-30 RES SMT 10 OHM 5% 1/8W 1206 R353,356, R358,359 RE-001502-10 RES MOFP 15 5% 2W MINI R209,210, R213,216, R367,368 R85-87,90, R93,208, RE-003921-30 RES SMT 39.2 OHM 1% 1/8W 120 R246-249, R349,357 R372 RE-005606-10 RES MOFP 56 5% 2W MINI RI24 RE-007502-30 RES SMT 75 1% l/l OW 1 OOV R5,6,123, Rl50,193, RE-010002-30 RES SMT 100 1% IIIOW IOOV RI 94,334, 24
RE-027401-30 RES SMT 274 1% l/l OW 1 OOV
RE-038301-30 RES SMT 383 1% l/lOW IOOV RE-047001-10 RES MOFP 470 5% 2W MINI
RE-047502.30 RES SMT 475 1% l/lOW IOOV RE-053602-30 RES SMT 536 1% l/l OW 1 OOV RE-063402-30 RES SMT 634 1% 1/8W 1206 RE-110006-30 RES SMT 1 .OOK 1% 1/8W 1206
RE-115002-30
RES SMT 1.5OK 1% l/lOW 1 OOV
RE-120002-30 RES SMT 2.OOK 1% l/l OW IOOV
RE-122103-30 RES SMT2.2lK 1% IIIOW IOOV
RE-139002-10 RES MOFP 3.9K 5% 2W MINI RE-147502-30 RES SMT 4.75K 1% l/l OW IOOV
RE-156001-10 RES 5.6OK .I% 1/4W 25PPM
RE-159002-30 RES SMT 5.9OK 1% l/lOW 1 OOV
RE-175002-30 RES SMT 7.5OK 1% l/l OW 1 OOV
RE-178701-30 RES SMT 7.87K 1% l/lOW IOOV RE-190902-30 RES SMT 9.09K 1% 1 /I OW 1 OOV
RE-210003-30 RES SMT lO.OK 1% l/lOW IOOV
RE-212702-30 RES SMT 12.7K 1% l/lOW IOOV
PLX 1202 PCB ASSEMBLY (12OV) Cont'd
Part Number Description Reference Rl34,139, Rl4,16,19, Rl42,169, Rl88,199, R200,241, R245,259, R329,337 R46,65, R76,77, Rl48,168, R25,45, R262,365 Rl72,173 R49,50, R31,153 Rl8,141, R229,242, R244,271~ R331,346 R325 R351,352 Rl43,183, Rl84,243, R20,60,61, R261,323, R332 R26,149 R156 R33,119, Rl76,196, Rl97,268, R341-345 R51,53>73, R74> 174, R333,335 R24,145, R260,263, R340 R321,322, R326,328 R339,371
PLX 1202 PCB ASSEMBLY (12OV) Cont'd
Part Number Description WC-0001 18-00 WIRE ASSY, BLK, LONG WC-000118-01 WC-0001 18-01 XF-000005-00 XF-000023-00 XF-000061-00 XF-000064-00 XF-000079-00 XF-000085-00 XF-200014-CR Reference
RE-212702-30 RES SMT 12.7K 1% l/lOW IOOV
RE-2 15002.30
RES SMT 15.OK 1% l/lOW IOOV
EHI-EH2 REF: WIRE ASSY, RED, SHORT ELI-EIZOA WIRE ASSY, RED, SHORT REF: BEAD FERRITE WI2OAWG LEAD L9,lO CHOKE COMMON MODE 2.2MH L3,4 INDUCTOR TORIOD 1.9UH 13GA L6 XFMR AMP HOUSEKEPPING PLC Tl T2 XFMR PLXI 202/2402 (12OV) XFMR PLXl202/2403 (IOOV) T3 INDUCTOR 2UH 14AWG VERT M Ll,2
RE-215401-30 RES SMT 15.4K