Adcom GFA-5200 Service manual

SERVICE MANUAL

2 CHANNEL

POWER AMPLIFIER

GFA-5200

TABLE OF CONTENTS

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

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

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

Specifications . . . . . . . . . . . . . . . 5

Chassis Layout . . . . . . . . . . . . . . . 5

PCB Layout . . . . . . . . . . . . . . . . . . 7

Wiring Diagram. . . . . . . . . . . . . . . . 8

Schematic . . . . . . . . . . . . . . . . . 9

10 Timber Lane

Marlboro, NJ 07746

USA

Tel: [phone]

Fax: [phone]

Web: http://www.adcom.com

INTRODUCTION

A

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This service manual is intended to assist trained and qualified technical personnel in verifying the
performance of, adjusting, and repairing the ADCOM GFA-5200 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-5200 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-5200 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-5200 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 with rated output (8 ohm) for
approximately 5 MINUTES before attempting adjustments

Step Coupling

Plus Lead Minus Lead

1 R035 R035 R038 DC Voltmete
2 R135 R135 R138 reads 20mV
3 L SPKR + L SPKR - R039 DC Voltmete
4 R SPKR + R SPKR - R139 reads 0mV

GFA-5300 SERVICE PARTS LIST

1

djust Adjust For

AMPLIFIER AND POWER SUPPLY PCB

FOR RIGHT CHANNEL REPLACE 0XX WITH 1XX

SCHMATIC ADCOM PART NUMBER DESCRIPTION
LOCATION

C001 12005385 CAPACITOR ELEC 47uF 63V
C002 12001415 CAPACITOR POLY 39pF 50V
C004 12001275 CAPACITOR MYLAR 2.2uF 250v
C005 12005325 CAPACITOR ELEC 4.7uF 50V
C006 12001425 CAPACITOR POLY 390pF 50V
C007 12005385 CAPACITOR ELEC 47uF 63V
C008 12001205 CAPACITOR MYLAR 1uF 250V
C010 XXXXXX CAPACITOR CTC 18pF
C011 12001235 CAPACITOR MYLAR 0.1uF 250V
C012 12005385 CAPACITOR ELEC 47uF 63V
C013 12002155 CAPACITOR CERAMIC 0.1uF 50V
C014 12005380 CAPACITOR ELEC 47uF 25V
C015 12005090 CAPACITOR ELEC 10uF 25V
C016 12001240 CAPACITOR MYLAR 0.01uF 50V
C017 12005160 CAPACITOR ELEC 22uF 25V
C018,C019 12001305 CAPACITOR MYLAR 0.22uF 250V
C020,C021 12005055 CAPACITOR ELEC 470uF 63V
C022,C023 12005005 CAPACITOR ELEC 10000uF 63V
C024,C025 12001235 CAPACITOR MYLAR 0.1uF 250V
C026,C027 12005010 CAPACITOR ELEC 1000uF 25V
C028 12002030 CAPACITOR CERAMIC 5pF 50V
D001-D005 16000082 DIODE ZENER 8.2V
D006,D007 16000082 DIODE ZENER 8.2V
D008,D009 16004148 DIODE 1N4148
D010 16001204 DIODE LTL1204 (RED)
D011 16001254 DIODE LTL1254 (YELLOW)
D012 16004003 DIODE 1N4003
D014-D017 16004003 DIODE 1N4003
D018 16005200 BRIDGE RECTIFIER KBPC2504
D058 16003600 DIODE ZENER 3.6V
M001,M002 19009400 FUSE GMA-4A
M006 32005200 THERMAL BREAKER UP72 85 DEGREE
Q001,Q002 33000992 TRANSISTOR 2SA992
Q003 33009210 TRANSISTOR IRFD9210
Q004 33001845 TRANSISTOR 2SC1845
Q005 33000992 TRANSISTOR 2SA992
Q006 33009610 TRANSISTOR IRF9610
Q007-Q009 33002100 TRANSISTOR IRFD210
Q011,Q012 33000610 TRANSISTOR IRF610
Q013 33002400 TRANSISTOR IRFP240
Q014 33000924 TRANSISTOR IRFP9240
Q015-Q017 33001845 TRANSISTOR 2SC1845
Q018 33000992 TRANSISTOR 2SA992
Q021 33008050 TRANSISTOR KTC8050
Q022 33008550 TRANSISTOR KTC8550
R003 27004620 RESISTOR 7.5K (1/4W 1% M.F.)
R004 27001515 RESISTOR 4.75R (1% 1/4W ROED)
R005 27004265 RESISTOR 2.2K (1/4W 1% M.F.)

SCHMATIC ADCOM PART NUMBER DESCRIPTION
LOCATION

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R006 27004640 RESISTOR 1.5K
R007 27004670 RESISTOR 100R
R008 27004570 RESISTOR 221R
R010,R012 27004200 RESISTOR 10K
R013 27004570 RESISTOR 221R
R014 27004300 RESISTOR 15K
R015 27004110 RESISTOR 2K
R016 27004135 RESISTOR 4.99K 1/2W
R017 27004570 RESISTOR 221R
R018 27004400 RESISTOR 1.82K
R019 27004600 RESISTOR 4.75K
R020,R021 27004500 RESISTOR 49.9K
R022 27004200 RESISTOR 10K
R023 27004400 RESISTOR 1.82K
R024 27004600 RESISTOR 4.75K
R026,R027 27004570 RESISTOR 221R
R028 27003200 RESISTOR 5.1R 2W
R030 27004225 RESISTOR 475R
R031 27004670 RESISTOR 100R
R034 27004570 RESISTOR 221R
R035,R036 27006095 RESISTOR 0.33R 3W
R037 27004570 RESISTOR 221R
R038 35001355 BIAS VR 5K
R039 35001355 DC OFFSET VR 5K
R041 27001480 RESISTOR 5.6K 2W
R042 27004500 RESISTOR 49.9K
R043,R044 27004570 RESISTOR 221R
R045,R046 27004670 RESISTOR 100R
R047 27004200 RESISTOR 10K
R048,R049 XXXXXX RESISTOR 56R
R050 27004160 RESISTOR 47.5K
R051 27004050 RESISTOR 1K
R052 27004435 RESISTOR 22R
R053 27004500 RESISTOR 49.9K
R054 27004200 RESISTOR 10K
R055 27004265 RESISTOR 2.2K
R056 27004630 RESISTOR 220K
R057 27004050 RESISTOR 1K
R058 27004071 RESISTOR 5.1K
R059 27001160 RESISTOR 33K
R060 27004500 RESISTOR 49.9K
R061,R062 27003280 RESISTOR 8.2K 1W
R063,R064 27003010 RESISTOR 10R 1/2W
R065,R066 27004071 RESISTOR 5.1K
R067,R068 27003010 RESISTOR 10R 1/2W
R140 27003300 RESISTOR 10R 2W
U001 21005550 IC LM555
22001380 JACK RCA INPUT GOLD

STANDBY POWER SUPPLY PCB

3

SCHMATIC ADCOM PART NUMBER DESCRIPTION
LOCATION

C201 12005700 SPARK KILLER 4700pF 400V
C202 12005010 CAPACITOR ELEC 1000uF 25V
C203 12005120 CAPACITOR ELEC 220uF 16V
D201-D205 16004003 DIODE 1N4003
D302 16001204 POWER LED LTL1204 (RED)
M204 37005200 POWER SWITCH SDDFA3066A
NR201 31005200 THERMISTOR 5R/8A
U201 21007812 REGULATOR IC 7812
V201 EURO 12001610 VARISTOR TNR9G391K
V201 USA 12001230 VARISTOR TNR9G221K

OTHERS

SCHMATIC ADCOM PART NUMBER DESCRIPTION
LOCATION

T1 24005200 MAIN TRANSFORMER 1806-2116-2
T2 24005201 STANDBY TRANSFORMER 1806-2196-0
M201 EURO 19000250 MAIN FUSE 2.5A 250V
M201 USA 19000500 MAIN FUSE 5A 125V
M202 EURO 19009050 STANDBY FUSE T.5A 250V
M202 USA 19009050 STANDBY FUSE T.5A 250V
13005201 FRONT PANEL
13005200 TOP COVER
13005204 HEAT SINK
13005205 HEAT SINK EXTENSION
47002580 LED HOLDER
13005206 FOOT
15001050 POWER CHORD
11001155 POWER BUTTON
11001165 POWER BUTTON FRAME
20005300 MAIN FUSE HOLDER

4

GFA-5200 SPECIFICATIONS

Power Rating (To FTC Requirements)

50 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
80 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 50 watts into 8 ohms............................................................................................................................... ≤ 0.07%

1 watt to 80 watts into 4 ohms............................................................................................................................... ≤ 0.07%

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

50 watts into 8 ohms............................................................................................................................................ ≤ 0.035%

80 watts into 4 ohms............................................................................................................................................ ≤ 0.035%

THD + Noise at 50 watts into 8 ohms (Typical)

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

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

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

20kHz....................................................................................................................................................................... 0.14%

THD + Noise at 80 watts into 4 ohms (Typical)

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

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

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

20kHz..................................................................................................................................................................... 0.165%

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

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

Dynamic Headroom into 4 ohms....................................................................................................................................... 2.2 dB

Signal to Noise Ratio, “A” Weighted (50 watts into 8 ohms) ......................................................................................... ≥ 98dB

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

Input Sensitivity

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

for 50 Watts......................................................................................................................................................... 0.71 volts

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

Damping Factor (20Hz to 20kHz)........................................................................................................................................ ≥ 260

Rise Time (5kHz, 90V, peak-to-peak square wave, 20% to 80%)...................................................................................... 1.1µS

Power Consumption (Continuous, All Channels Driven)

Quiescent.................................................................................................................................................................. 50VA

Maximum................................................................................................................................................................. 600VA

50 watts into 8 ohms................................................................................................................................................ 325VA

80 watts into 4 ohms................................................................................................................................................ 480VA

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

Chassis Dimensions.............................................................................................. 3” (72mm) x 17” (432mm) x 11 3/8” (289mm)

Maximum Dimensions..................................................................................... 3 1/4” (83mm) x 17” (432mm) x 12 1/8” (308mm)

Weight...................................................................................................................................................................... 17 lb. (7.7 kg)

Weight, Packed ..................................................................................................................................................... 22 lb. (10.0 kg)

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