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1、SERVICE MANUAL 5 CHANNEL POWER AMPLIFIER GFA-7605 TABLE OF CONTENTS Introduction . . . . . . . . . . . . . . . . 1 Test Procedures . . . . . . . . . . . . . 1 Parts List . . . . . . . . . . . . . . . . . . 2 Voltage Conversion . . . . . . . . . . . . 5 Specifications . . . . . . . . . . . . . . . 7
2、PCB Layouts. . . . . . . . . . . . . . . . . . 8 Schematic . . . . . . . . . . . . . . . . . 9 8551 East Anderson Drive,Suite 105 Scottsdale, Arizona 85255 USA Tel: 480-607-2277 Fax: 480-348-9876 Web: http:/ RadioFans.CN 收音机爱 好者资料库 1 INTRODUCTION This service manual is intended to assist trained and
3、 qualified technical personnel in verifying the performance of, adjusting, and repairing the ADCOM GFA-7605 amplifier. The procedures described here are not intended for persons unfamiliar with the appropriate safety and test procedures. TEST PROCEDURES All tests are performed with a 115V, low-disto
4、rtion (less than 2% THD), AC-power source, 8-ohm resistive load (except slew rate), and a signal source of not more than 600 ohms. An 80kHz low-pass filter is employed during THD distortion measurements. Signal-to-noise measurements are “A” weighted. Damping factor is measured by comparing the 1 wat
5、t output voltage with and without an 8 ohm load. Slew rate is measured with an inductive load, and is derived with a dual-time-based oscilloscope reading the slope of a full power 5kHz square wave. DO NOT OPERATE THE AMPLIFIER AT FULL-POWER SINE WAVE ABOVE 22kHz OR FULL-POWER SQUARE WAVE ABOVE 5kHz.
6、 CORRECT BIAS ADJUSTMENT IS CRITICAL TO THE PERFORMANCE OF THIS AMPLIFIER. MAXIMUM OUTPUT POWER, MINIMUM THD AND HEAT DISSIPATION ARE AFFECTED BY THE BIAS SETTING AND MUST BE CORRECT TO MAINTAIN THE SONIC QUALITY AND LONGEVITY OF THE AMPLIFIER. BIAS ALIGNMENT The component references are the same fo
7、r all channels. Operate the amplifier without load or input connection for this adjustment. 1. Turn the amplifier on and allow to idle for 5 minutes. 2. Connect millivoltmeter across emitter resistor R36. Adjust bias pot R25 for a 10mV +/- 1mV reading. NOTE: The bias adjustment must be performed wit
8、h the heatsink attached and the amplifier module installed in the chassis. The best way to perform the bias adjustment is by connecting one probe of millivoltmeter to emitter of Q15 (lowest pin) and connecting the other probe to the positive (red) speaker output. DC OFFSET CHECK 1. Connect a millivo
9、ltmeter across the speaker output terminals and confirm a reading of 0mV +/- 10mV. WARNING THERE ARE POTENTIALLY LETHAL VOLTAGES WITHIN THE GFA-7605 AMPLIFIER WHICH WILL BE ACCESSIBLE ONCE ITS TOP COVER IS REMOVED. DO NOT ATTEMPT FAMILIARIZATION, INSPECTION, OR ANY PROCEDURE WHATSOEVER UNLESS YOU HA
10、VE DISCONNECTED THE GFA-7605 FROM THE WALL AC OUTLET OR OTHER SOURCE OF AC POWER AND THE POWER-SUPPLY CAPACITORS ARE COMPLETELY DISCHARGED. THESE INSTRUCTIONS ARE PROVIDED FOR USE ONLY BY COMPETENT TECHNICAL PERSONNEL. DO NOT UNDERTAKE ANY SERVICE PROCEDURES IN THE GFA-7605 UNLESS YOU ARE TECHNICALL
11、Y QUALIFIED TO DO SO. IMPORTANT BEFORE PROCEEDING WITH ADJUSTMENTS, MAKE SURE AMPLIFIER IS AT ROOM TEMPERATURE. RadioFans.CN 收音机爱 好者资料库 2 GFA-7605 SERVICE PARTS LIST AMPLIFIER MODULE PCB SCHEMATIC ADCOM PART NUMBER DESCRIPTION LOCATION BR2 BRIDGE RECTIFIER SBU8G C01 CAPACITOR POLY FILM 2.2uF 100V C0
12、2 CAPACITOR POLY FILM 330pF 100V C03 CAPACITOR ELEC 100uF 63V C04 CAPACITOR MYLAR FILM 1uF 100V C05 CAPACITOR SILVER MICA 33pF 100V C06 CAPACITOR POLY FILM 4.7nF 100V C07 CAPACITOR ELEC 10uF 25V C08 CAPACITOR ELEC 100uF 100V C09 CAPACITOR ELEC 100uF 100V C10 CAPACITOR POLY 270pF 100V C11 CAPACITOR P
13、OLY 270pF 100V C12 CAPACITOR ELEC 100uF 10V C13 CAPACITOR MYLAR 0.1uF 250V C15 CAPACITOR ELEC 10uF 25V C16 CAPACITOR POLY 0.01uF 100V C17 CAPACITOR ELEC 22uF 35V C18 CAPACITOR ELEC 10000uF 63WV C19 CAPACITOR ELEC 10000uF 63WV C20 CAPACITOR MYLAR 0.22uF C21 CAPACITOR MYLAR 0.22uF C22 CAPACITOR ELEC 1
14、00uF 16V C23 CAPACITOR ELEC 220uF 25V D02-D05 DIODE 1N4148 D08,D09 DIODE 1N4007 D10-D13 DIODE 1N4148 F3 FUSE T6.3A F4 FUSE T6.3A J1 RCA INPUT JACK LED1 DISTORTION LED LTL1254 (YELLOW)LED2 PROTECT LED LTL1204 (RED) Q01 TRANSISTOR 2SC3381 Q02 TRANSISTOR MPSA92 Q03 TRANSISTOR MPSA42 Q04 TRANSISTOR MPSA
15、92 Q05 TRANSISTOR MPSA92 Q06 TRANSISTOR MPSA92 Q07 TRANSISTOR 2SA1380 Q08 TRANSISTOR 2SC3502F Q09 TRANSISTOR 2SC1567 Q10 TRANSISTOR 2SC4793 Q11 TRANSISTOR 2SA1837 Q12 TRANSISTOR 2SC3281 Q13 TRANSISTOR 2SA1302 Q14 TRANSISTOR 2SC3281 Q15 TRANSISTOR 2SA1302 Q16 TRANSISTOR MPSA42 Q17 TRANSISTOR MPSA42 Q
16、18 TRANSISTOR MPSA42 RadioFans.CN 收音机爱 好者资料库 3 SCHEMATIC ADCOM PART NUMBER DESCRIPTION LOCATION R01 RESISTOR 1K R02 RESISTOR 4.99K R03 RESISTOR 4.99K R04 RESISTOR 49.9K R05 RESISTOR 1K R06 RESISTOR 22.1 R07 RESISTOR 249 R08 RESISTOR 347 R09 RESISTOR 22.1 R10 RESISTOR 4.99K R11 RESISTOR 1.78K R12 RES
17、ISTOR 49.9K R13 RESISTOR 4.99K R14 RESISTOR 75K R15 RESISTOR 249 R16 RESISTOR 5.6K 1/2W R17 RESISTOR 4.99K R18 RESISTOR 100 R19 RESISTOR 475 R20 RESISTOR 37.4 R21 RESISTOR 37.4 R22 RESISTOR 75 R23 RESISTOR 2.74K R24 RESISTOR 1K R26 RESISTOR 392 R27 RESISTOR 392 R28 RESISTOR 10 R29 RESISTOR 49.9 R30
18、RESISTOR 49.9 R31 RESISTOR 10 R32 RESISTOR 33.2 R33-R36 RESISTOR 0.33 3W R37 RESISTOR 2.21K R38 RESISTOR 22.1K R39 RESISTOR 33.2 R40 RESISTOR 5.1 2W R41 RESISTOR 10K R42 RESISTOR 2.21K R43 RESISTOR 221K R44 RESISTOR 2.21K R45 RESISTOR 4.99K R46 RESISTOR 22.1K R47 RESISTOR 6.8K 2W R48 RESISTOR 6.8K 2
19、W TB1 THERMAL BREAKER TH2 THERMISTOR CL150 U1 IC LM555 VR25 BIAS POT 200 RadioFans.CN 收音机爱 好者资料库 4 POWER SUPPLY PCB SCHEMATIC ADCOM PART NUMBER DESCRIPTION LOCATION C01 CAPACITOR ELEC 1000uF 25V C18 SPARK KILLER C02 CAPACITOR ELEC 220uF 16V D1-D6 DIODE 1N4004 F1 MAIN FUSE 12A F2 STANDBY FUSE 1A K1 T
20、URN-ON RELAY LED1 POWER LED LTL1204 (RED) Q1 TRANSISTOR MPSA13 R1 RESISTOR 1K 1W R2 RESISTOR 3.32K R3 RESISTOR 10K R4 RESISTOR 3.32K T1 STANDBY TRANSFORMER TH1 THERMISTOR CL100 U2 REGULATOR IC 7812 POWER SWITCH OTHERS SCHEMATIC ADCOM PART NUMBER DESCRIPTION LOCATION T2 T2 MAIN TRANSFORMER MAIN TRANS
21、FORMER Multi Voltage Models115VAC only Models FOOT FRONT PANEL HEATSINK POWER BUTTON POWER BUTTON FRAME TOP COVER RadioFans.CN 收音机爱 好者资料库 5 GFA-7605 Voltage Conversion The GFA-7605 amplifier is produced in both a 120VAC only version and a multivoltage (120VAC or 230VAC convertible) version. The vers
22、ion can usually be distinguished by external inspection. The 120VAC only version has a fixed AC line cord. The convertible version has a detachable line cord. Internally, their are two differences. The toroid transformer in the convertible version has 2 primaries; the first primary has a black and b
23、rown lead, the second primary has a black and brown lead with white stripe. The toroid transformer in the 120VAC only version has only the brown and black lead (1 primary winding). Additionally, the connecting block mounted next to the power switch is different in both versions. In the multivoltage
24、unit, this connecting block has 5 pair of mounting leads (as is shown in the figures below). In the 120VAC only version, the connecting block has only 3 pairs of mounts. The conversion procedure for the multivoltage GFA-7605 unit is listed below. Conversion of Multivoltage Units 120V to 230V 1. Unpl
25、ug the amplifier and remove the top cover. 2. Locate the connecting block mounted next to the power switch. 3. Move the transformer leads so they are configured as shown in figure 1. 4. Remove heavy gauge wire connections between screw down portion of terminals. 4. Change the rear panel AC fuse from
26、 12A to 6A, AGC. Place a sticker on the rear panel at the fuse holder to show the new value fuse (6A) and new value operating voltage (230VAC). 5. Test the unit with a 230VAC source. Figure 1: Transformer lead configuration for 230VAC operation (multivoltage units) RadioFans.CN 收音机爱 好者资料库 6 230V to
27、120V 1. Unplug the amplifier and remove the top cover. 2. Locate the connecting block mounted next to the power switch. 3. Move the transformer leads so they are configured as shown in figure 2. 4. Add heavy gauge wire between screw down portion of terminals as shown. 4. Change the rear panel AC fus
28、e from 6A to 12A, AGC. Place a sticker on the rear panel at the fuse holder to show the new value fuse (12A) and new value operating voltage (120VAC). 5. Test the unit with a 120VAC source. Figure 2: Transformer lead configuration for 120VAC operation (multivoltage units) RadioFans.CN 收音机爱 好者资料库 7 G
29、FA-7605 SPECIFICATIONS Power Rating (To EIA/CEA-490-A Requirements) 125 watts continuous average power per channel into 8 ohms at any frequency between 20Hz to 20kHz with all channels driven at less than 1.00% THD 150 watts continuous average power per channel into 4 ohms at any frequency between 20
30、Hz to 20kHz with all channels driven at less than 1.00% THD IM Distortion (SMPTE) 1 watt to 100 watts into 8 ohms. 0.075% 1 watt to 150 watts into 4 ohms. 0.075% IM Distortion (CCIF, Any Combination from 4kHz to 20kHz) 100 watts into 8 ohms. 0.025% 150 watts into 4 ohms. 0.025% THD + Noise at 100 wa
31、tts into 8 ohms (Typical) 20Hz. 0.0012% 1kHz. 0.0012% 10kHz. 0.02% 20kHz. 0.025% THD + Noise at 150 watts into 4 ohms (Typical) 20Hz. 0.025% 1kHz. 0.025% 10kHz. 0.035% 20kHz. 0.045% Frequency Response 1 Watt into 8 ohms (10Hz to 20kHz). +0, -0.25dB Power Bandwidth (-3dB). 1.5Hz to 65kHz Dynamic Head
32、room into 4 ohms. 2.5 dB Signal to Noise Ratio, “A” Weighted (100 watts into 8 ohms). 110dB Gain. 29dB Input Sensitivity for 1 Watt. 0.1 volts for 100 Watts. 1.0 volts Input Impedance . 50k Damping Factor (20Hz to 20kHz). 400 Rise Time (5kHz, 90V, peak-to-peak square wave, 20% to 80%). 4.5S Power Co
33、nsumption (Continuous, All Channels Driven) Quiescent. 96VA Maximum. 1440VA 100 watts into 8 ohms. 1165VA Power (Available in 230VAC on special order). 115VAC - 50/60Hz Chassis Dimensions. 5” (127mm) x 17” (432mm) x 14” (355.6mm) Maximum Dimensions. 5 3/4” (146mm) x 17” (432mm) x 15” (381mm) Weight. 42 lb. (19.1 kg) Weight, Packed . 48 lb. (22.8 kg) RadioFans.CN 收音机爱 好者资料库 8 RadioFans.CN 收音机爱 好者资料库
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