QSC_MX1500,_MX2000_Service_Manual 电路图.pdf

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1、RadioFans.CN 收音机爱 好者资料库 TABLE OF CONTENTS MX1500 Specifications . 3 MX1500 Printed Circlrit Layotit until thermal shutdown occurs. The exact short circuit current limits are adjusted by 2K trimmers TR2 and TR3. Output Protection 2nd Signal Readout Circuits There are three circuit protect functions;

2、turn-onloff muting, thermal shutdown, and DC protection. The power for protect circuit operation is taken from the +46V output supply and an independent -24V power supply from the low voltage transformer secondary (through D4 and R32 and filtered by E5). A high-current relay is t in series with the

3、speaker output; switched by small transistors Q17 and Q18. liode Dl8 absorbs inductive kickback when the relay is shut off. NOTE: The relay connects the load to ground when not activated. Ts not only helps protect the load from DC fault, but enables the bridged mono a:, 1 back-up feature. When the a

4、mp first is turned on, the relay contacts are cpen and no sound appears in the speakers. With no current through the relay, the +8mA flowing through R12 from the positive supply lights the red section of the bicolor protecVpower LED. E7 is initially discharged and takes about three seconds to charge

5、 to the point where R29 can turn on Q18. Q17 sends -20ma through the relay, turning on the speaker and overcoming the +8 ma into the pilot LED; reversing it to green. LD6 in series with Ql8 creates a -2.2V threshold at thc base of Q18 (1.6V + .6V). When the pilot LED is red, it has +I .6V across it,

6、 which means that the total voltage across R30 must be 3.8V before Q18 can turn on. When E7 reaches -l5V, R29 will send enough current to get 3.8V across R30. Q18 turns on, driving Q17 and the relay. When the relay turns on, the voltage across the pilot LED is reversed. R30 sends positive feedback f

7、rom this event back to Q18, which ensures a positive latching on or off. When the amp is turned off, E5 quickly discharges, removing power from the relay, and resetting E7 through D17. Thermal protection is accomplished by using a PTC (Positive Temperature Coefficient) resistor attached to the heat

8、sink. The +8ma from R12 flows through this part. Below 75C, the resistance remains at 100 ohms, which means that there is less than 1V dropped across the PTC. As temperature exceeds 80C, the resistance of the PTC goes up and the voltage drop increases. As the voltage reaches 3V, the flashing circuit

9、 (E3, R59-61, C11, Q20-21, driving Thermal LED LD1) is activated (through R13). This signals the user that temperatures are nearing the limit. When the temperature reaches about 95C, the voltage across the PTC reaches 6V; enough to turn off Q18 through the 7.5V zener 217. This shuts off the relay an

10、d removes the load until the amp cools down and the PTC resistance returns to approximately I k ohms. DC protection is accomplished with another auxiliary circuit. R27 and E6 filter the audio output. If the frequency drops below 10Hz or if DC appears for more than .I second, the voltage on E6 will r

11、ise to 2V. This forward biases the bridge rectifier 82 and turns on Q19. Q19 is connected to the rectifier so that either polarity of DC will trigger it. When Q19 turns on, it discharges E7 and shuts off the relay. The recharge time of E7 prevents destructive chattering of the relay. IMPORTANT: The

12、entire relay circuit is referenced to the power supply, not to ground. Be careful when measuring or substituting parts, to keep track of what voltages you are connecting to. InpuVOutput Connections The 114-inch and barrier strip input jacks are connected in parallel. The input connections are made t

13、o the circuit board through a 6 contact modular telephone-type connector. The speaker output connectors are 5-way binding posts. The speaker grounds are connected together. The speaker and power supply connections are made with an 8 contact connector on the circuit board. TROUBLESHOOTING THE NIX1 50

14、0lMX2000 AMPLIFIER Please refer to the MX1500 schematic for the component identification numbers in this troubleshootitg guide, Excessive Current Draw The amplifier draws abnormal current when AC power is first applied (wit11 or without signal, but without output load). A. HIGH CURRENT DRAW, WITH NO

15、 OUTPUT SIGNAL (greater than 10 amps at 3OVAC) 1, Shorted bridge rectifier B 1 or B2. 2 . Solder shorts on printed circuit board (from previous repair job?). 3. Supply clamping diodes D7, D 10 shorted. 4. Outplts or driver tratlsistors shorted on both supplies (NPN Reduce afTected step cap. C7 or C8

16、 by 50%, try new Q22, 23, sometimes helps, in severe cases, add 470 pF capacitor frotn collector-base of Q3 or Q4 as necessary. 4. Fuzzy glitch (LISLIIY 4 olilns or lower): checldiucrease affec* ci step speedup capacitor C7 or C8 by 25-50% 5: Spike: Check C7 or C8 (as above) or consult on ossibility

17、 of A ? yF (inax) across collector- base of upper driver transistor. 6: Severe at 2-4 011111s: step circuit switclirg late: values of Z15 c : f nlay need to be altered, Q23 or Q22 open, or R57lD1 1 or R58lD14 in series are iissinglwr-3 -1:. 7. Crossover Jistortion: (Notcll or ringing at zero crossin

18、g) Severe: shorted bias diode, defective trimmer cornpc lbntu. Moderate: out-of-spec bias diodes, defective trimnit- co;iiponents. 8. Cant get notch 011 mininli1111 setting: see above, aid check for b : k rcc;istors on output devices. 9. Instability on one side: add .OlSuF trimner bypass capacitor a

19、*- :I TRI. Chmge the values of the driver emitter capacitors C9, C 10. 10. Overall Itlstability: The outpt signal is usually distorted and is :i!:illy worse at a particular part of tlie output waveforin. (Do not confuse with 60- 120Hz. in t 1 . outj.tut signal, which spreads the signal trace evenly

20、and vertically. lderltify this problert I-)y reducing the scope sweep rate to 101ms range and use LINE sync to look for 60-124)I-i hum eqiiemcies.) I I. Severe instability at all loads, often with excessive current ( *:v: tisually a bad or nissing slew rate capacitor (C3) or feedback capacitor C2. 1

21、2. Medium instability, especially on low signals or 8 oh111 or Iiig i tvpedance loads: 13. A stability component is defective or not soldered well: fee? k capacitor C2, secondary stability apacitors (9-10 (jump with a comparable v:ilue, see if -: .r-stB, if so try replacing with 50% lower value). 14

22、. If the oscillation occurs wit11 very low gain, suspect an opet? -ircr!it in the feedback shunt R81E4 (or a broken circit trace). 15. Replace the 1C and check tlie IC socket for contarnination. 1 6. Harnonic Distortion: These can be tough as sonietines cause i buried illstability whicli is sioothed

23、 out by later stages. Tliis can be checked by probing IC c1 ut, and using stability procedures above to iliiprove. Otherwise: IS it Odd (3rd order) or Even (second order) distortion? Odd indicates an equal problem on both sides of zero, nonnaf.; a p,ut hmdling the full signal swing. Eve11 indicates

24、a nisniatch between positive 31. negative, usually a bad part on one side of tlie circuit. Pc - Frequency Response 1. High freq, determined by illput rolloff C 1, and feedback capaci t i 12 (wrong value also causes instability) 2. Low freq, detern ined by DC feedback roI loff E4, and butterwt s f 1

25、feedback compensation network C4/R9 (see also Gain section). Gain Wrong 1. Too high: Missing one of the two feedback resistors fro111 output, R7 or R9; or inpnt Rl-4 is wroig value. (Fawlty jnput resistors will cause the ainplifier to fail the CM test,) 2. Too law: Above feedback valiies wrong or s1

26、1unt resistor R8/E4 wrong or open (open causes very low gain with instability. Check circuit trace) incorrect Short Circuit Current Limits 1. The sliort circuit currelit is too high: a. If the IC l5VDC supply checks nonnal (5-6 volts): defective Z 15- 16 zeners or shorted bias diode D5-6 (shows seve

27、re crossover). b. If the IC I 5VDC supply is too Iiigh (one or both supplies above 8VDC): c. Replace the IC (poor output current), d. Otie or lnore of the CLIP componelits is open: clip LED (LD2), feed resistor R1 1, 1.5A rectifier B1. 2. If the IC 15VDC siipply rails are low into a short aid a 2 oh

28、m load (oflerl on one side of tlie s11pply only): a. Cleck for a defective chargeback diode D8 or D9 (tlie atnp tnay liave prenlature clipping at 4 olins as well). b. IS the IC supply is OK until clipping the amp rnay have low gain devices above the step. See tliat a11 tipper oirtpitts and emitter r

29、esistors are present and that the supply feed resistors (R33-34) are OK. An upper driver transistor may liave very low gain. c. If the clippiiig wavefonn collapses into a near-tricm.ngul;tr signal (instead of flat-top clipping), the +/- 15V supply filter capacitors may be defective. If both capacito

30、rs are aging equally, you may have to replace then1 to test tliis solutiotl. D. C. Fault Without Current Draw In rnatly cases, sllorts in tile circuit will cause current draw, but certain sliorts will olily cause DC offset in the output. I11 both cases, measuring all the voltages, Iookilg for abnonn

31、al values can help trace the fault, wliicli can be a solder short (zero volts), reversed Zener or diode (.6V) reversed electrolytic (several volts), or wrong value parts (abnormal voltage). Look at the following points in tlie circuit. 1 . Slorted IC rai 1, sometimes both sIlorted together; includin

32、g mod jack. 2. Reversed ISV Zener Z 13,14 gives .6V on 1C rail. Zero volts i f blown. 3, TR 2 or TR3 all the way off or way too low in value. 4. Collector-base short on driver (rare without further damage). Sometines IC forces the rest of the circuit into DC due to slorts in the feedback network, et

33、c. To check tliis, remove XC, check for +15V, -15V, and see if adjusting current limit trimmers TR2,3 will produce a zero volt output (there will be no signal, of course). If so, output stage is probably OK, look for probletns in IC, or its associated parts. 5, Defectivelreversed 1C (pull and check

34、voltages) Protection Circuit Troubleshoo ting Note: all voltages are wit11 respect to SPEAKER BUS. If ail-eplifier itself is OK, yotr cai conveniently neasiire voltages to ground by turning SIGNAL LEVEL OFF (so there is zero volts on speaker bus). Relay Wont Come On Check speaker bus for DC; if over

35、 3V DC present, tile protect circuit is operating nonnally to Ilold off operation. If tlo DC present, collti111e below: 1. Check Relay power voltage. With relay off, voltage at E5 shoulti tlzeastre -47V (with relay 011, about 27V). Lfnot, check R32, D4, D18, E5 polarity. 2. Power OK, check voltage o

36、n tin3ing capacitor E7. Shottld rise to 12-15V, in three seconds, wliiclr triggers Q 18. If not check R28, R29, E7 polarity. 3. Timing voltage OK; clxeck relay tramistor Q 17. If good, a 47K rsistor from base to speaker bus should activate relay. 4. Relay Q 17 OK, check driver Q 18 and LED LD6. If t

37、he relay cat) be forced 01.1 by shorting Q 17 (and the protect circuit stays 011) clleck Z 17, Q 19, Ql8, alci R3 l . No Red Protect LED 1. Check voltage on LED while relay is off. If over +2V, LED is b3d. If OV (no positive drive), there is no protect power (missing R 12), whic11 defeats all sllitd

38、oavn circuits. No Muting Delay (No Thermal or DC Protect Either; relay or circuit is sttrck OII) I. Relay Q 17 shorted or wrongly stuffed. Check by jumping bast: to emitter, should turn it off. 2. Driver 018 shorted or wrongly stuffed (check by jtrmping b:? ,z to emitter). Excess Muting Delay I . Ch

39、eck timing capacitor E7 voltage. T f it rises ilortnally but circtl:t slow to tun1 on, check 217 (lifi temporarily), LD-6 bad or intermittent, R30 too low. 2. Timing capacitor voltage wrong; deternine cause (R28,29, reversed E7, rnissiig R62, reversedlwong Q 19) No Thermal Shutoff 1. Put voltmeter a

40、cross PTC and look for voltage to rise .From .7V c l d to 5.5V shutdown. 2. No Red Protect, No Flaslzing; inay have no K12, wkich defeat: wllole tliennal circuit (no voltage across PTC). 3. Flashes but wont s11ut down; check 217 higWmissing, or R13 ions, or relay drive circuit stlck on (see above).

41、4. Red protect lR12 OK, but no voltage across PTC; kfective or slrorted (Iifi temporarily, shotrid themal off imiiediately). 1. R2, Q 19 open 2. Replace LD-6 if voltage is less than 1.5V. Relay Faults With Nornally Operating Amplifier 1. Checlc Relay power voltage. With relay off, voltage at ES shou

42、ld tneasure -47V (with relay on, about 27V)(E803 shorld rnc2asurt. -53 y). If not, checIs R32, D4, 318, E5 polarity. 2. Power OK, check voltage on tinling capacitor E7. Should rise to 12- 1 SV, in three seconds, which triggers Q18. If not check R28, R29, E7 polarity. 3. Timing voltage OK; clieck rel

43、ay transistor Q17, If good, a 47K -esistor from base to speaker bus should activate relay. 4. Relay Q 17 OK, check driver Q 18 and LED LDG. MX 2000 Parts List1 of 3 MX 2000 Power Amplifier Parts List NPN PCB Assembly (2 per amplifier) QSC part # WP-160046-PC QSC Part #DescriptionQty. ReferenceCommen

44、ts CA-147100-BD470PF, 100V, 10%, DISK1 CA-210100-BP.001UF,100V,10%,MYLAR1 CA-368100-BP.068UF,100V,10%,MYLAR1 CA-410160-BPOBS-.1UF,160V,10%,MYLAR1 CA-822100-BE2200UF, 100V, ELEC, RADIAL,10%4 CA-833080-BE3300UF, 80V, ELEC., RADIAL,10%2 CA-168100-BD680PF,100V,10%,DISK1 CH-350208-GXOBS-3500 HEAT XFMR BR

45、ACKET FAB1 HW-060100-PS#6-32 X 10 PEM STUD5 HW-060200-SPOBS-9222-A140 AMATOM SPACER5 MS-000066-HSTO-66 HEATSINK AAVID #E5020B2 NW-000220-RWOBS-TO-220 RECT. WASHER2 NW-060010-SL#6 SPLIT TOOTH LOCKWASHER6 NW-060400-HN#6-32 X 1/4 HEX NUT5 NW-060410-STA-4 SPRING TOOTH LOCKWASHER3 PC-380046-HXOBS-3800 NP

46、N PCB1 PL-000025-PLOBS-9222-PH140 AMATOM SPACER2 PL-000026-PLOBS-TO-220 X 1 TEK-SIL INSLTOR2 PL-003109-SPOBS-NYLON SPACER2 PL-905100-SPSPACER,ROUND,NYLON,#6,0.100L4 PT-250000-AT5K OHM TRIMPOT1 QD-000424-TXOBS-2SD424,TRANSISTOR,NPN,TO-310 QD-0004.7-ZTDIODE,ZENER,4.7V TESTED1 QD-000810-DXTO-220 8A/100

47、V DIODE,FAST2 QD-002763-TU2A, TO-220,PNP UNTESTED TRANS2 QD-004934-DX1N4934 DIODE3 QD-005402-DX1N5402 DIODE1 QD-008599-TXMPS 8599 TRANSISTOR, PNP1 RE-.02205-FWRESISTOR,WIREWOUND,0.22 10% 3W10 RE-.33005-DMRESISTOR,METAL FLM,3.3 5% 1W1 RE-001005-EMRESISTOR,METAL FLM,10 5% 2W8 RE-001505-DMOBS-15 OHM, 1

48、W, MET. OX. 5%2 RE-010005-BCRESISTOR,CRBN FLM, 100 5% 1/4W1 RE-015005-BCRESISTOR,CRBN FLM,150 5% 1/4W1 RE-082005-BCRESISTOR,CARBON, 820 5% 1/4W1 RE-115005-BCRESISTOR,CARBON,1.5K 5% 1/4W1 RE-130053-HWRESISTOR,WIREWOUND,3K 5% 5W1 SC-060061-PP#6-32 X 3/8 P/P BLACK4 SC-062050-PP#6 X 5/16 “B” P/P ZINC20

49、WC-0.6022-JW.6 JUMPER, 22 GA, SLD3 WC-0.9022-JW.9 JUMPER, WHITE, 22 GA, SLD2 WC-2.5018-JW2.5 JUMPER, WHT, 18 GA, SLD3 XF-200014-CR2UH, 14 GA, COIL/VERTICAL2 PNP PCB Assembly (2 per amplifier) QSC part # WP-160047-PC QSC Part #DescriptionQty. ReferenceComments CA-168100-BD680PF,100V,10%,DISK1 CA-210100-BP.001UF,100V,10%,MYLAR2 CA-222100-BP.0022UF,100V,10%,MYLAR1 CA-