QSC III Series, Technical & Service Manual

Page 1: ...Series III Power Amplifiers TECHNICAL SERVICE MANUAL 3800 R E V B TD 300001 AX 3500 3350 3200...

Page 2: ...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...

Page 3: ...3 SERIES THREE POWER AMPLIFIERS...

Page 4: ...Diagram 18 Detailed Explanations 18 Troubleshooting Chart 23 Introduction 23 1 Current Draw Section 23 2 Protection Circuit Problems 24 3 Faults With Signal Present 25 Series Three Test Procedures 29...

Page 5: ...d in parallel 2 terminal barrier strip and 5 way binding post outputs wired in parallel octal input sockets provided for input transformers or active accessories ground lift terminal block Cooling Pas...

Page 6: ...allel 2 terminal barrier strip and 5 way binding post outputs wired in parallel octal input sockets provided for input transformers or active accessories ground lift terminal block Cooling Passive coo...

Page 7: ...s wired in parallel 2 terminal barrier strip and 5 way binding post outputs wired in parallel octal input sockets provided for input transformers or active accessories ground lift terminal block Cooli...

Page 8: ...signal level indicators flashing over temp indicators Cooling Passive cooling combined with high efficiency output stage for 50 reduction in dissipated heat Unique circuit configuration provides dire...

Page 9: ...BP 001UF 100V 10 MYLAR C1 C9 D9 D18 C10 C15 QD 004410 TX BJTN 80V 25A 1 5W 2N4410 Q9 Q13 CA 222100 BP 0022UF 100V 10 MYLAR C3 Q14 CA 347050 BP 047UF 50V 10 MYLAR C7 C8 QD 004744 ZA ZENER 15V 1W 5 1N4...

Page 10: ...BC 5 1K 1 4W 5 CF R6 RE 210001 BM RESISTOR MF 10 OK 1 1 4 R1 R2 R3 R4 RE 212101 CM 12 1K 1 2W 1 MF R7 RE 210005 BC 10K OHM 1 4W CARBON 5 R45 RE 230005 BC 30K 1 4W 5 CF R46 RE 242201 BM RESISTOR 42 2K...

Page 11: ...DGE RECT QD 0003 9 ZT ZENER 3 9V 25W DZ84073ID Z15 PL 003 65 TW TIE WRAP 4 BLACK SMALL QD 0004 7 ZT ZENER 4 7V 25W DZ840731E Z16 PL 000011 TW TIE WRAP 11 WHITE LONG QD 0007 5 ZT ZENER 7 5V 25W DZ84073...

Page 12: ...CF R11 R20 R21 R61 RE 010005 CC 100 1 2W 5 CF R32 RE 033201 BM 332 1 4W 1 MF R8 RE 033005 HW 330 OHM 5 WATT WW 10 R52 RE 015005 BC 150 1 4W 5 CF R57 R58 RE 110005 BC 1K 1 4W 5 CF R5 RE 110005 EM 1K 2...

Page 13: ...ULATOR D21 D22 LB 100003 SR ON SUBPANEL PL 903125 SP SPACER ROUND NYLON 0 047 L1 L2 LB 376002 MP ON SUBPANEL R14 MS 350410 HS HEAT SINK PL 905385 SP SPACER RND NYL 6 0 385 L B LD1 LD2 MS 350472 SP SUB...

Page 14: ...000050 NR NTC THERMISTOR 50 OHM R14 RE 001005 EM 10 2W 5 MOFP R56 RE 002205 DM 22 1W 5 MOFP R15 R16 R17 R18 RE 010005 BC 100 1 4W 5 CF R11 R20 R21 R61 RE 018005 CC 180 1 2W 5 CF R32 RE 033201 BM 332...

Page 15: ...NW 060410 ST A 4 SPRING TOOTH LOCKWASHER P NW 060400 HN 6 32 BY 1 4 HEX NUT P D5 D6 PC 000046 AM MAIN NPN BOARD PL 000220 MI D5 D6 PL 905100 SP SPACER ROUND NYLON 6 0 L1 L2 PT 250000 AT RES VAR IT 5K...

Page 16: ...M 6 8 OHM 1W MET OXIDE 5 R13 NW 060410 ST LCKWSHR ON HEAT XFER BRKT MTG PEMS RE 247005 BC 47K 1 4 W 5 CF R11 NW 060400 HN 6 32 BY 1 4 HEX NUT PEMS RE 210005 BC 10K OHM 1 4W CARBON 5 R2 R12 PC 000047 B...

Page 17: ...BG GAIN PCB BOARD PL 905385 SP SPACER RND NYL 6 0 385 L B LD1 LD2 LD3 LD4 LD5 PL 909235 SP HOLDER LED 90 DEGREES NY LD1 LD2 LD3 LD4 LD5 QD 000134 LR LED RED T 1 3 4 LD1 LD2 QD 000134 LX LED R G T 1 3...

Page 18: ...e power supplies are DC coupled with the usual transformer center tap We use a speaker relay for DC protection as discussed in section 6 The second unusual feature is that we reverse the usual locatio...

Page 19: ...ermined by the base current to each driver through 1K resistors and 3 9V zener diodes R19 and R22 Z15 and Z16 When the op amp rails are at their normal 15V this current is about 9ma and results in abo...

Page 20: ...an at full output By having a lower level DC supply for lower levels of output voltages up to 50 we greatly reduce waste voltage and power for lower level signals Of course the big problem is to switc...

Page 21: ...2V This is enough to forward bias the bridge rectifier B2 and turn on Q19 Note that Q19 is connected to the rectifier so that either polarity of DC will trigger it When Q19 turns on it discharges E7...

Page 22: ...22...

Page 23: ...r pins a hard short solder short will read virtually zero volts A reading of 0 6 1V above ground indicates a reversed diode or shorted output A reading of 1 2 volts could mean a bad driver but outputs...

Page 24: ...is enough to activate zener diode Z17 which turns off the base of Q18 which is at 2 2V when on and shuts off the relay circuit The latching effect holds the circuit off until the PTC voltage has coole...

Page 25: ...too small of a resistance a low voltage on E7 turns Q18 on too soon d Missing or too large of a resistance at R30 no off current 3 Possible causes of an excess muting delay a Check the voltage across...

Page 26: ...the current is too low into a shorted output as well as a 2 ohm load check a If the IC rails are o k some possible causes are i Bias resistor R19 or R22 measures too high ii Very low gain resistors se...

Page 27: ...an indicate a problem in minor stability components see that section above b Also check the output filter R56 L2 R49 R50 C5 and inner coil R55 and L1 c Alternatively the crossover or step may be large...

Page 28: ...s bad d Possible causes of high frequency distortion i The value of C3 is too high x10 for the slew rate compensation capacitor ii The base resistors R15 R16 R17 or R18 on the output devices are missi...

Page 29: ...visible on the positive and negative halves of the waveform still into no load on channel B of the oscilloscope d Switch the load to 8 ohms and vary the amplifier gain just above and below the step sw...

Page 30: ...2 output and observe power output at 20Hz 0 5dB max and 20kHz 0 5dB max 10 Temperature cycle a Switch to the 2 6 ohm load Increase the signal to the point of clipping and short the output of the ampli...

Page 31: ...isible on the positive and negative halves of the waveform still into no load on channel B of the oscilloscope d Switch the load to 8 ohms and vary the amplifier gain just above and below the step swi...

Page 32: ...or 9 5dB output and observe power output at 20Hz 0 5dB max and 20kHz 0 5dB max 10 Temperature cycle a Switch to the 2 ohm load Increase the signal to the point of clipping and short the output of the...

Page 33: ...sible on the positive and negative halves of the waveform still into no load on channel B of the oscilloscope d Move the wiring harness and tap the circuit boards with a non conductive implement such...

Page 34: ...r Select a 2kHz signal input to the amplifier b Adjust the amp gain to obtain 215 watts x2 or 7 5dB output and observe power output at 20Hz 0 5dB max and 20kHz 0 5dB max 10 Temperature cycle a Switch...

Page 35: ...veform still into no load on channel B of the oscilloscope d Switch the load to 8 ohms and vary the amplifier gain just above and below the step switching level Watch for obvious step oscillation This...

Page 36: ...0W x 2 10 Temperature cycle a Switch to the 2 ohm load Increase the signal to the point of clipping and short the output of the amplifier The clip LED should be on Check for recovery into 2 ohms cold...

Page 37: ...Series Three Schematics Model3200...

Page 38: ...Model 3350...

Page 39: ...Model 3500 Early Version...

Page 40: ...Model 3500 Late Version...

Page 41: ...Model 3800...

Page 42: ...Series Three PCB Drawings Model 3200 PCB...

Page 43: ...Model 3350 PCB...

Page 44: ...Model 3800 46A PCB...

Page 45: ...Model 3800 47A PCB...

Page 46: ...Model 3800 48B PCB...

Page 47: ...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...