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
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
1
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 |
2
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