QSC III Series Technical & Service Manual
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QSC III Series Technical & Service Manual

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Series III
Power Amplifiers
T E C H N I C A L S E R V I C E M A N U A L
3200
3350
3500
R E V . B
*TD-300001-AX*
3800

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Summary of Contents for QSC III Series

  • Page 1 Series III Power Amplifiers T E C H N I C A L S E R V I C E M A N U A L 3200 3350 3500 R E V . B *TD-300001-AX* 3800...
  • Page 2 SERVICE MANUAL Series Three Power Amplifiers QSC Audio Products Inc. Technical Services Group Toll Free: 800-772-2834 Local: 714-957-7150 Fax: 714-754-6173 QSC Audio Products, Inc. 1675 MacArthur Blvd. Costa Mesa, CA 92626 www.qscaudio.com tech_support@qscaudio.com...
  • Page 3 SERIES THREE POWER AMPLIFIERS...

  • Page 4: Table Of Contents

    Table of Contents Product Specifications Model 3200 Model 3350 Model 3500 Model 3800 Series Three Parts Lists 3200 PCB ASSEMBLY 3350 PCB ASSEMBLY 3500 PCB ASSEMBLY 3800 MAIN NPN PCB ASSEMBLY 3800 MAIN PNP PCB ASSEMBLY 3800 GAIN PCB ASSEMBLY Series Three Power Amplifiers Circuit Description Block Diagram...

  • Page 5: Product Specifications

    Product Specifications Model 3200 OUTPUT POWER (per channel) Cooling: Passive cooling combined with high efficiency output stage for reduced operating Continuous Average Output Power both channels temperatures. Unique circuit configuration driven: allows direct metal mounting of output devices 8 ohms, 20 Hz-20 kHz 0.1% THD 110 W for reduced thermal stress from short-term...

  • Page 6: Model 3350

    Model 3350 Cooling: OUTPUT POWER (per channel) Passive cooling combined with high efficiency output stage for reduced operating Continuous Average Output Power both channels temperatures. Unique circuit configuration driven: allows direct metal mounting of output devices 8 ohms, 20 Hz-20 kHz 0.1% THD 200 W for reduced thermal stress from short-term 1 kHz...

  • Page 7: Model 3500

    Model 3500 OUTPUT POWER (per channel) Cooling: Passive cooling combined with high efficiency output stage for reduced operating Continuous Average Output Power both channels temperatures. Unique circuit configuration driven: allows direct metal mounting of output devices 8 ohms, 20 Hz-20 kHz 0.1% THD 300 W for reduced thermal stress from short-term 1 kHz...

  • Page 8: Model 3800

    Model 3800 OUTPUT POWER (per channel) Cooling: Passive cooling combined with high efficiency Continuous Average Output Power both channels output stage for 50% reduction in dissipated driven: heat. Unique circuit configuration provides 8 ohms, 20 Hz-20 kHz 0.1% THD 375 W direct-metal mounting of output devices to 1 kHz 1% THD...

  • Page 9: Series Three Parts Lists

    PL-905385-SP SPACER RND, NYL #6 0.385"L B LD1, LD2, J7, J10 LD3, LD4, WC-0.8022-JW .8" JUMPER, WHITE J2, J11 WC-001102-SQ INSUL.SLEEVE QSC 1102,.6" CLRPTC PL-909235-SP HOLDER, LED, 90 DEGREES, NY LD1, LD2, WC-1.1022-JW 1.1 JUMPER WHITE 22GA J4, J5 LD3, LD4,...
  • Page 10 3200 PCB ASSEMBLY, Cont'd WP-320038-PO 3200 MAIN PCB ASSY Part Number Description Reference RE-139005-CC RE-147005-DM 4.7K 5% MOFP RE-151005-BC 5.1K 1/4W 5% CF RE-210001-BM RESISTOR, MF 10. OK 1% 1/4 R1, R2, R3, R4 RE-212101-CM 12.1K 1/2W 1% MF RE-210005-BC 10K OHM, 1/4W, CARBON 5% RE-230005-BC 30K 1/4W 5% CF RE-242201-BM RESISTOR,42.2K,1/4W,MET FM 1%R9 RE-239005-BC 39K,1/4W,CARBON 5%...

  • Page 11: 3350 Pcb Assembly

    SW-000010-RY MX1500/3500 24V OUTPUT RELAY NW-060410-ST LCKWSHR-PEM STUD-HEAT XFER BRKT MTG. XF-200016-CR IND 2UH 16GA AIR L1, L2 PC-000040-FM MAIN PCB WC-001102-SQ INSUL.SLV QSC 1102,.6", CLR PL-000220-MI D21, D22 WC-003018-TQ BLUE, FROM HOLE POS. #1&2 TO B4 PL-903125-SP SPACER, ROUND, NYLON 0.047 L1, L2, WC-003019-TQ BRN., FROM HOLE POS.
  • Page 12 3350 PCB ASSEMBLY, Cont'd WP-335040-TC 3350 MAIN PCB ASSY Part Number Description Reference RE-.33005-DM 3.3 MOFP R25, R26 RE-.56005-BC 5.6 1/4W 5% CF RE-.56005-EM 5.6 2W 5% MOFP RE-000000-PT 90 C PTC RESISTOR RE-000050-NR NTC THERMISTOR, 50 OHM RE-001005-EM 10 2W 5% MOFP RE-002205-DM 22 1W 5% MOFP R15, R16, R17, R18...

  • Page 13: 3500 Pcb Assembly

    MS-000220-HS HEATSINK, TO-220 AAVID#5943B Q3, Q4 XF-200016-CR IND 2UH 16GA AIR L1, L2 CH-350208-GX HEAT TRANSFER BRKT. WC-001102-SQ INSUL. SLV QSC 1102,.6", CLR PTC NW-000220-RW TO-220 RECT. WASHER D21, D22 WC-003018-TQ BLUE, FROM HOLE POS. #1&2 TO B4 NW-060010-SL #6 SPLIT TOOTH LOCK WASHER Q1, Q2, WC-003019-TQ BRN., FROM HOLE POS.
  • Page 14 3500 PCB ASSEMBLY, Cont'd WP-350040-PC 3500 MAIN PCB ASSY REV Q Part Number Description Reference QD-004934-DX DIODE100V 1A 200NS VP 1N493 D1, D2, D3, D5, D6, D8, D9, D11, D12, D14, QD-008599-TX BJTP 60V .5A .625W MPS8599 Q18, Q19, Q21, Q22 QD-1.5200-BX DIODE BRIDGE RECT 200V, 1.5A B1, B2 RE-.01505-FW .15 OHM 3W 10% RESISTOR R35, R36,...

  • Page 15: 3800 Main Npn Pcb Assembly

    3800 MAIN NPN PCB ASSEMBLY WP-380046-NP 3800 QSC46A MAIN PCB ASSY WP-380046-NP 3800 QSC46A MAIN PCB ASSY Part Number Description Reference Part Number Description Reference CA-147100-BD 470PF, 100V, 10%, DISK WC-0.6022-JW .6" JUMPER, WHITE J1, J2, CA-210100-BP .001UF, 100V, 10%, MYLAR CA-368100-BP .068UF, 100V, 10%, MYLAR WC-0.9022-JW JMPR INS 0.9"...

  • Page 16: 3800 Main Pnp Pcb Assembly

    QD-000810-DX DIOD 100V 8A 35NS MUR809 D8, D9 WC-0.9022-JW JMPR INS 0.9" 22AWG SLD WHT QD-001848-TH SJ1848 NPN TO-66/TO-213AA Q1, Q2 WC-001102-SQ INSUL. SLV QSC 1102,.6",CLR QD-004004-DX DIODE RECT DO41 400V 1A D1, D2, PL-003109-SP SLEEVE D8, D9 D3, D4 WC-2.5018-JW JMPR INS 2.5"...

  • Page 17: 3800 Gain Pcb Assembly

    3800 GAIN PCB ASSEMBLY WP-380048-GN GAIN BOARD ASSY Part Number Description Reference CA-018100-CM (REPLACED WITH CA-018001-10) C4 CA-047100-BD 47PF, 100V, 10%, DISK CA-210100-BP .001UF, 100V, 10%, MYLAR CA-215100-BP .0015UF, 100V, 10%, MYLAR CA-410100-BP .1UF, 100V, 10%, MYLAR CA-412100-CP .12UF, 100V, 5%, MYLAR CA-547016-BN 4.7UF, 16V, 20% LYTIC NP CA-647010-BN 47UF, 10V, 10% RAD, CAP LYTICE4 CA-722010-BN 220UF 10V CAPACITOR...

  • Page 18: Series Three Power Amplifiers

    For unbalanced inputs, either input line may be grounded and the circuit will respond at unity gain to the other line. For reasons of overall stability in actual use, QSC uses the inverting input for unbalanced signals.
  • Page 19 LED. One of the featured advantages of the QSC circuit is our effective short circuit protection. In order to maintain good audio performance into low impedance loads, it is necessary to maintain a high output current limit. The normal current limit is determined by the base current to each driver through 1K resistors and 3.9V zener diodes (R19 and...
  • Page 20 25 A peak. Here you will see another unique feature of the QSC circuit. Note that the collectors of all output transistors meet at a common ground. (This is possible because of the special power supply arrangement, as described in Section 1.) This means we can simply screw the cases of all four banks to a grounded heat sink, with no need for the usual insulating mica.
  • Page 21 When the amp is turned on, the relay contacts are open and no sound comes from the speakers. With no current through the relay, the +8mA flowing through R12 from the positive supply makes the red section of the bicolor protect/power LED light up.

  • Page 23: Troubleshooting Chart

    Series Three Power Amplifiers Troubleshooting Chart (5-1-85) Introduction This troubleshooting chart refers to parts by their function in the circuit, and also by the part numbers for our popular models 3350 and 3500 amplifier. The circuits for the 3200 and 3800 are basically the same but the part numbering is different;...

  • Page 24: Protection Circuit Problems

    2. Protection Circuit Problems CIRCUIT OPERATION. The Speaker output relay is switched by Q17, which is driven by Q18. Diode D18 absorbs inductive kickback from the relay when shut off. There are three distinct protect functions; turn-on/off muting, thermal shutdown, and DC protection. RELAY POWER.

  • Page 25: Faults With Signal Present

    Relay Faults with Normally Operating Amplifier 1. If the relay won’t turn on, a. Check the relay power voltage. With the relay off, voltage at E5 should measure –54V on a 3800, -47V on a 3500, -39V on a 3350, and –32V on a 3200. With the relay on, all amplifiers should have about 27V across E5.
  • Page 26 Turn the gain knobs up until the output of the amp is at the threshold of clipping. b. If one side clips too early, the circuit of the opposite polarity has the problem (this is a usual feature of QSC amplifier designs).
  • Page 27 c. Measure the voltage or place a scope probe on the lower driver emitter resistors, R25 or R26. d. Replace the driver transistor if it has weak current (indicated by low voltage), its drive is low (see above) or if its gain is low. If the driver shows equal or greater current, it is good and is trying to overcome a weakness in the outputs or upper level driver.
  • Page 28 iii. R57, D11 or R58, D14 in series are missing or bad 5. General or overall distortion a. Before anything else, wiggle or otherwise check the input and output connectors for good contact. If there is good contact, troubleshooting overall distortion can be tough since the cause is sometimes buried instability, which is smoothed out by later stages.

  • Page 29: Series Three Test Procedures

    Series Three Test Procedures: Model 3200 1. Inspection a. Carefully inspect the amplifier module for burned or damaged components. 2. Hook-up a. Connect load resistors, oscilloscope channel A (20V/Div.), and distortion analyzer (1000 Watt/0.1% input/distortion) to the amplifier output. Note: the output may be measured before the relay at the center tap (pins 7 and 8 of the 8-pin connector) b.
  • Page 30 b. Select a load resistance of 2.6 ohms. Vary the Gain to display a small amount of ordinary voltage clipping (indicated by the presence of ripple at peaks of the output signal). Note: Check that the red clip LED is working. c.

  • Page 31: Model 3350

    Test Procedures: Model 3350 1. Inspection a. Carefully inspect the amplifier module for burned or damaged components. 2. Hook-up a. Connect load resistors, oscilloscope channel A (20V/Div.), and distortion analyzer (1000 Watt/0.1% input/distortion) to the amplifier output. Note: the output may be measured before the relay at the center tap (pins 7 and 8 of the 8-pin connector) b.
  • Page 32 b. Select a load resistance of 2 ohms. Switch to a 20A meter. Vary the Gain to display a small amount of ordinary voltage clipping (indicated by the presence of ripple at peaks of the output signal). Note: Check that the red clip LED is working. c.

  • Page 33: Model 3500

    Test Procedures: Model 3500 1. Inspection a. Carefully inspect the amplifier module for burned or damaged components. 2. Hook-up a. Connect load resistors, oscilloscope channel A (20V/Div.), and distortion analyzer (1000 Watt/0.1% input/distortion) to the amplifier output. Note: the output may be measured before the relay at the center tap (pins 7 and 8 of the 8-pin connector) b.
  • Page 34 a. Select an 8-ohm load. b. Change the input frequency to 20kHz and decrease the input level to 20dB. Adjust the crossover trimpot, T1, for 3 CM peak-to-peak of crossover spike protruding from the noise signal on channel B of the oscilloscope. Note: The bias shouldn’t need adjusting unless the amp is over-heating or the drivers have been changed.

  • Page 35: Model 3800

    Test Procedures: Model 3800 1. Inspection a. Carefully inspect the amplifier module for burned or damaged components. 2. Hook-up a. Connect load resistors, oscilloscope channel A (20V/Div.), and distortion analyzer (1000 Watt/0.1% input/distortion) to the amplifier output. Note: the output may be measured before the relay at the center tap (pins 7 and 8 of the 8-pin connector) b.
  • Page 36 a. Adjust the input signal for 260W (-7dB) of output power. b. Select a load resistance of 2 ohms. Vary the Gain to display a small amount of ordinary voltage clipping (indicated by the presence of ripple at peaks of the output signal). Note: Check that the red clip LED is working.

  • Page 37: Series Three Schematics

    Series Three Schematics Model3200...

  • Page 38: Model 3350

    Model 3350...

  • Page 39: Model 3500 Early Version

    Model 3500 Early Version...

  • Page 40: Model 3500 Late Version

    Model 3500 Late Version...

  • Page 41: Model 3800

    Model 3800...

  • Page 42: Series Three Pcb Drawings

    Series Three PCB Drawings Model 3200 PCB...

  • Page 43: Model 3200 Pcb

    Model 3350 PCB...

  • Page 44: Model 3350 Pcb

    Model 3800 46A PCB...

  • Page 45: Model 3800 46A Pcb

    Model 3800 47A PCB...

  • Page 46: Model 3800 47A Pcb

    Model 3800 48B PCB...

  • Page 47: Model 3800 48B Pcb

    Model 3800 Gain PCB...
  • Page 48 QSC Audio Products, Inc. 1675 Mac Arthur Blvd Costa Mesa CA 92626 Tel 714-754-6175 Fax 714-754-6173...

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