Adcom GFA-5503 Service manual

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SERVICE MANUAL

3 CHANNEL

POWER AMPLIFIER

GFA-5503

TABLE OF CONTENTS

Introduction . . . . . . . . . . . . . . . . 1

Test Procedures . . . . . . . . . . . . . 1

Parts List . . . . . . . . . . . . . . . . . . 2

Voltage Conversion . . . . . . . . . . . . 5

Specifications . . . . . . . . . . . . . . . 7

Schematic . . . . . . . . . . . . . . . . . 8

8551 East Anderson Drive, Suite 105

Scottsdale, Arizona 85260

USA

Tel: 480-607-2277

Fax: 480-348-9876

Web: http://www.adcom.com

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INTRODUCTION

This service manual is intended to assist trained and qualified technical personnel in verifying the performance of, adjusting, and repairing the ADCOM GFA-5503 amplifier. The procedures described here are not intended for persons unfamiliar with the appropriate safety and test procedures.

WARNING

THERE ARE POTENTIALLY LETHAL VOLTAGES WITHIN THE GFA-5503 AMPLIFIER WHICH WILL BE ACCESSIBLE ONCE ITS TOP COVER IS REMOVED. DO NOT ATTEMPT FAMILIARIZATION,

INSPECTION, OR ANY PROCEDURE WHATSOEVER UNLESS YOU HAVE DISCONNECTED THE GFA-5503 FROM THE WALL AC OUTLET OR OTHER SOURCE OF AC POWER AND THE POWERSUPPLY CAPACITORS ARE COMPLETELY DISCHARGED. THESE INSTRUCTIONS ARE PROVIDED FOR USE ONLY BY COMPETENT TECHNICAL PERSONNEL. DO NOT UNDERTAKE ANY SERVICE PROCEDURES IN THE GFA-5503 UNLESS YOU ARE TECHNICALLY QUALIFIED TO DO SO.

TEST PROCEDURES

• All tests are performed with a 115V, low-distortion (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 watt 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.

IMPORTANT

BEFORE PROCEEDING WITH ADJUSTMENTS, MAKE SURE AMPLIFIER IS AT ROOM

TEMPERATURE.

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

Prior to performing BIAS ALIGNMENT turn unit on and allow to idle for approximately 5 MINUTES before attempting adjustments.

1. Connect millivoltmeter across emitter resistor R52 for left channel (R52 for center channel, R51 for

right channel)

2. Adjust bias pot P2 until meter reads 50mV +/- 5mV

DC OFFSET ADJUSTMENT

1. Connect millivoltmeter across speaker output

2. Adjust DC offset pot P1 until meter reads 0mV +/- 10mV

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a GFA-5503 SERVICE PARTS LIST

AMPLIFIER MODULE PCB

SCHEMATIC ADCOM PART NUMBER DESCRIPTION LOCATION

C01 XXXXX CAPACITOR 390pF 100V C02 12001075 CAPACITOR 2.2uF 100V C03 12005280 CAPACITOR ELEC 47uF 50V C04 12001085 CAPACITOR 0.22uF 100V C05 12001480 CAPACITOR SILVER MICA 15pF 100V C06 12001470 CAPACITOR SILVER MICA 20pF 100V C07 12005325 CAPACITOR ELEC 4.7uF 50V C09 12005380 CAPACITOR ELEC 47uF 25V F1,F2 19000800 RAIL FUSE 8A 250V LED1 16001204 THERMAL LED LTL1204 (RED) LED2 16001254 DISTORTION LED LTL1254 (YELLOW) P01 35001550 DC OFFSET POT 5K P02 35001550 BIAS POT 5K Q01,Q02 33002100 TRANSISTOR IRFD210 Q03,Q04 33000092 TRANSISTOR MPSA92 Q05 33007570 TRANSISTOR ZTX757 Q06 33009210 TRANSISTOR IRFD9210 Q07 33009610 TRANSISTOR IRF9610 Q08 33002100 TRANSISTOR IRFD210 Q09 33006570 TRANSISTOR ZTX657 Q10,Q11 33000610 TRANSISTOR IRF610 Q12 33000042 TRANSISTOR MPSA42 Q13 33006570 TRANSISTOR ZTX657 Q14 33007570 TRANSISTOR ZTX757 Q14 33000092 TRANSISTOR MPSA92 Q15 33002400 TRANSISTOR IRFP240 Q16 33000924 TRANSISTOR IRFP9240 Q17 33002400 TRANSISTOR IRFP240 Q18 33000924 TRANSISTOR IRFP9240 Q19 33002400 TRANSISTOR IRFP240 Q20 33000924 TRANSISTOR IRFP9240 Q21 33002400 TRANSISTOR IRFP240 Q22 33000924 TRANSISTOR IRFP9240 Q23 33002400 TRANSISTOR IRFP240 Q24 33000924 TRANSISTOR IRFP9240 R01 27001565 RESISTOR ROED 221R R02 27002480 RESISTOR ROED 1.82K R03 27002365 RESISTOR ROED 49.9K R04 27002480 RESISTOR ROED 1.82K R05 27002030 RESISTOR ROED 10K R06 27002280 RESISTOR ROED 15K R07 27002170 RESISTOR ROED 475R R08 27001565 RESISTOR ROED 221R R09 27001565 RESISTOR ROED 221R R10 27002010 RESISTOR ROED 100R R11 27002030 RESISTOR ROED 10K R12 27002365 RESISTOR ROED 49.9K R13 27002240 RESISTOR ROED 7.5K

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SCHEMATIC ADCOM PART NUMBER DESCRIPTION LOCATION

R14 27002025 RESISTOR ROED 1.5K R15 27002030 RESISTOR ROED 10K R16 27002500 RESISTOR ROED 33.2K R16A 27002500 RESISTOR ROED 33.2K R17 27001565 RESISTOR ROED 221R R18 27001565 RESISTOR ROED 221R R19 27001515 RESISTOR ROED 4.75R R20 27002010 RESISTOR ROED 100R R21 27002030 RESISTOR ROED 10K R22 27002200 RESISTOR ROED 4.99K R23 27001530 RESISTOR ROED 2.74K R24 27003035 RESISTOR 5.1K 1W R25,R26 27002410 RESISTOR ROED 4.75K R27,R28 27003390 RESISTOR 220R 1/2W R29,R30 27003090 RESISTOR 47R 1/2W R32 27002365 RESISTOR ROED 49.9K R33-R42 27003390 RESISTOR 220R 1/2W R43-R52 27006045 RESISTOR 0.68R 5W R53 27002030 RESISTOR ROED 10K TB101 32006000 THERMAL BREAKER Z01-Z08 16000082 DIODE ZENER 8.2V

POWER SUPPLY PCB

SCHEMATIC ADCOM PART NUMBER DESCRIPTION LOCATION

BR1-BR3 16003504 BRIDGE RECTIFIER 300V 35A C02 12001235 CAPACITOR 0.1uF 250V C04 12001235 CAPACITOR 0.1uF 250V C06 12001235 CAPACITOR 0.1uF 250V C08 12001235 CAPACITOR 0.1uF 250V C10 12001235 CAPACITOR 0.1uF 250V C12 12001235 CAPACITOR 0.1uF 250V C13 12001235 CAPACITOR 0.1uF 250V C16 12001235 CAPACITOR 0.1uF 250V C19 12001235 CAPACITOR 0.1uF 250V C22 12001235 CAPACITOR 0.1uF 250V C25 12001235 CAPACITOR 0.1uF 250V C28 12001235 CAPACITOR 0.1uF 250V C14,C15 12005265 CAPACITOR ELEC 1000uF 100V C17,C18 12005265 CAPACITOR ELEC 1000uF 100V C20,C21 12005265 CAPACITOR ELEC 1000uF 100V C23,C24 12005265 CAPACITOR ELEC 1000uF 100V C26,C27 12005265 CAPACITOR ELEC 1000uF 100V C29,C30 12005265 CAPACITOR ELEC 1000uF 100V C01 12005525 CAPACITOR ELEC 18,000uF 100V C03 12005525 CAPACITOR ELEC 18,000uF 100V C05 12005525 CAPACITOR ELEC 18,000uF 100V C07 12005525

CAPACITOR ELEC 18,000uF 100V

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SCHEMATIC ADCOM PART NUMBER DESCRIPTION LOCATION

C09 12005525 CAPACITOR ELEC 18,000uF 100V C11 12005525 CAPACITOR ELEC 18,000uF 100V D01-D12 16004004 DIODE 1N4004 R11,R12 27003300 RESISTOR 10R 2W R17,R18 27003300 RESISTOR 10R 2W R23,R24 27003300 RESISTOR 10R 2W R09,R10 27003355 RESISTOR 15K 2W R15,R16 27003355 RESISTOR 15K 2W R21,R22 27003355 RESISTOR 15K 2W R07,R08 27003365 RESISTOR 22R 2W R13,R14 27003365 RESISTOR 22R 2W R19,R20 27003365 RESISTOR 22R 2W R25 27003335 RESISTOR 6.8K 1W R1-R6 27003280 RESISTOR 8.2K 2W TH1-TH3 31005500 THERMISTOR CL40

OUTPUT PCB

SCHEMATIC ADCOM PART NUMBER DESCRIPTION LOCATION

30005800 BINDING POST C8 12001235 CAPACITOR 0.1uF 250V R31 27001000 RESISTOR 4.7R 2W

OTHERS

SCHEMATIC ADCOM PART NUMBER DESCRIPTION LOCATION

C31 12005700 SPARK KILLER 0.01uF 1500V F3 19001200 MAIN FUSE 15A 250V TH4 33005500 THERMISTOR CL40 13005500 FRONT PANEL 13005504 HEATSINK LEFT 13005505 HEATSINK RIGHT 37001325 POWER SWITCH 22001170 RCA INPUT JACK 13005501 TOP COVER 13005805 FOOT

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a GFA-5503 Voltage Conversion

The GFA-5503 amplifier is produced in both a 120VAC only version and a multivoltage (120VAC or 230VAC convertible) version. The version 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 brown 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 unit, this connecting block has 6 pair of mounting leads (as is shown in the figures below). In the 120VAC only version, the connecting block has only 4 pairs of mounts.

The conversion procedure for the multivoltage GFA-5503 unit is listed below.

Conversion of Multivoltage Units

120V to 230V

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 1.

4. Change the rear panel AC fuse from 15A to 8A, AGC. Place a sticker on the rear panel at the fuse holder to show the new value fuse (8A) and new value operating voltage (230VAC).

5. Test the unit with a 230VAC source.

White

(from AC fuse)

KC103P

KCC

CL-10

Black/White (to xformer)

Brown/White

(to xformer)

Black

(to xformer)

(to xformer)

Figure 1: Transformer lead configuration for 230VAC operation (multivoltage units)

230V to 120V

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Brown

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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. Change the rear panel AC fuse from 8A to 15A, AGC. Place a sticker on the rear panel at the fuse holder to show the new value fuse (15A) and new value operating voltage (120VAC).

5. Test the unit with a 120VAC source.

White

(from AC fuse)

KC103P

KCC

CL-10

Black/White (to xformer)

Black

(to xformer)

Brown/White

(to xformer)

Figure 2: Transformer lead configuration for 120VAC operation (multivoltage units)

Brown

(to xformer)

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GFA-5503 SPECIFICATIONS

Power Rating (To FTC Requirements)

200 watts continuous average power per channel into 8 ohms at any frequency between 20Hz to 20kHz with all channels driven at less than 0.18% THD 350 watts continuous average power per channel into 4 ohms at any frequency between 20Hz to 20kHz with all channels driven at less than 0.18% THD

IM Distortion (SMPTE)

1 watt to 200 watts into 8 ohms............................................................................................................................. ≤ 0.05%

1 watt to 350 watts into 4 ohms............................................................................................................................. ≤ 0.05%

IM Distortion (CCIF, Any Combination from 4kHz to 20kHz)

200 watts into 8 ohms............................................................................................................................................ ≤ 0.04%

350 watts into 4 ohms............................................................................................................................................ ≤ 0.04%

THD + Noise at 200 watts into 8 ohms (Typical)

20Hz....................................................................................................................................................................... 0.018%

1kHz......................................................................................................................................................................... 0.02%

10kHz....................................................................................................................................................................... 0.07%

20kHz....................................................................................................................................................................... 0.13%

THD + Noise at 350 watts into 4 ohms (Typical)

20Hz....................................................................................................................................................................... 0.018%

1kHz......................................................................................................................................................................... 0.02%

10kHz....................................................................................................................................................................... 0.08%

20kHz....................................................................................................................................................................... 0.16%

Frequency Response @ 1 Watt into 8 ohms (10Hz to 20kHz)................................................................................. +0, -0.25dB

Power Bandwidth (-3dB) ....................................................................................................................................... 3Hz to 130kHz

Dynamic Headroom into 4 ohms....................................................................................................................................... 1.7 dB

Signal to Noise Ratio, “A” Weighted (200 watts into 8 ohms) ..................................................................................... ≥ 100dB

Gain........................................................................................................................................................................................ 29dB

Input Sensitivity

for 1 Watt............................................................................................................................................................... 0.1 volts

for 200 Watts......................................................................................................................................................... 1.4 volts

Input Impedance................................................................................................................................................................ 49.9kΩ

Damping Factor (20Hz to 20kHz)........................................................................................................................................ ≥ 700

Rise Time (5kHz, 90V, peak-to-peak square wave, 20% to 80%)...................................................................................... 1.5µS

Power Consumption (Continuous, All Channels Driven)

Quiescent................................................................................................................................................................ 199VA

Maximum................................................................................................................................................................. 855VA

80 watts into 8 ohms.............................................................................................................................................. 1440VA

125 watts into 4 ohms.............................................................................................................................................. 720VA

Power (Available in 230VAC on special order)................................................................................................. 115VAC - 50/60Hz

Chassis Dimensions.................................................................................................. 7” (178mm) x 17” (432mm) x 16” (406mm)

Maximum Dimensions......................................................................................... 7 1/4” (184mm) x 17” (432mm) x 16” (406mm)

Weight....................................................................................................................................................................... 57 lb. (20 kg)

Weight, Packed ........................................................................................................................................................ 63 lb. (23 kg)

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