Adcom GFA-5400 Service manual

SERVICE MANUAL

2 CHANNEL

POWER AMPLIFIER

GFA-5400

TABLE OF CONTENTS

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

Version 1 vs. Version 2........1

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

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

Specifications...............6

Chassis Layout . . . . . . . . . . . . . . . 7

Version 1 Schematic..........8

Version 2 Schematic..........9

10 Timber Lane

Marlboro, NJ 07746

USA

Tel: [phone]

Fax: [phone]

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-5400 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-5400 AMPLIFIER WHICH WILL
BE ACCESSIBLE ONCE ITS TOP COVER IS REMOVED.

INSPECTION, OR ANY PROCEDURE WHATSOEVER UNLESS YOU HAVE DISCONNECTED THE
GFA-5400 FROM THE WALL AC OUTLET OR OTHER SOURCE OF AC POWER AND THE POWER­SUPPLY CAPACITORS ARE COMPLETELY DISCHARGED

PROVIDED FOR USE ONLY BY COMPETENT TECHNICAL PERSONNEL.

ANY SERVICE PROCEDURES IN THE GFA-5400 UNLESS YOU ARE TECHNICALLY QUALIFIED
TO DO SO.

VERSION 1 vs. VERSION 2

There are 2 versions of the GFA-5400 amplifier. The primary difference between the original version 1
and the updated version 2 is the addition of the ADCOM output protection circuit in version 2. This circuit
can be noted by comparing the schematics of both versions in this manual. The protection circuit in
version 2 includes trigger ICs IC711 and IC712 and a second power supply of standby transformer
TT002, rectifier D701 and regulator IC701 that is mounted to a small circuit board at the right front hand
side of the unit. The power transformer, speaker binding posts and input jacks are also unique to each
version.

DO NOT ATTEMPT FAMILIARIZATION,

. THESE INSTRUCTIONS ARE

DO NOT UNDERTAKE

Besides these distinctions, the amplifier circuit, parts reference numbers and values are nearly identical in
both units. Even so, a schematic diagram for both versions is included in this manual. The parts list is for
version 2 but contains an addendum section to list parts exclusive to version 1. The board and chassis
layout diagrams are for version 2 only. The alignment procedures are the same for both versions.

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.

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.

DO NOT OPERATE THE AMPLIFIER AT

BIAS ALIGNMENT and DC OFFSET CHECK

Prior to performing BIAS ALIGNMENT and DC OFFSET CHECK turn unit on and allow to run with rated
output for approximately

5 MINUTES

before attempting adjustments

1

Step Couplin

g

Adjust Adjust For

Plus Lead Minus Lead

1 R675 R675 VR603 DC Voltmeter
2 R676 R676 VR604 reads 35mV
3 L SPKR + L SPKR - VR601 DC Voltmeter
4 R SPKR + R SPKR - VR602 reads 0mV

GFA-5400 SERVICE PARTS LIST

a

a

aa

Power Supply PCB
AF608615

SCHEMATIC ADCOM PART NUMBER DESCRIPTION
LOCATION

C901-C904 12005565 CAPACITOR ELECTROLYTIC 12000uF 63V
C905-C908 12001185 CAPACITOR MP 0.1uF 250V
C909-C912 12005420 CAPACITOR ELECTROLYTIC 1000uF 16V
C913-C916 12005195 CAPACITOR ELECTROLYTIC 470uF 100V
C917-C920 12001185 CAPACITOR MP 0.1uF 250V
D903-D914 16004003 DIODE 1N4003
R901-R904 27001590 RESISTOR 5.6K 1W MOF
R905-R912 27005030 RESISTOR ROED. 10 1/2W FUSABLE
R913-R916 27003280 RESISTOR ROED. 8.2K 2W 5% METAL
TH901, TH902 31000512 THERMISTOR SCK0512

Amplifier PCB
AF608625, AF608635

SCHEMATIC ADCOM PART NUMBER DESCRIPTION
LOCATION

C601,C602 12003175 CAPACITOR STYROL 390pF 125V
C603,C604 12001260 CAPACITOR MP 2.2uF 100V
C605,C606 12005470 CAPACITOR ELECTROLYTIC 47uF 100V
C607,C608 12001020 CAPACITOR LAYER 1uF 50V
C609,C610 12005325 CAPACITOR ELECTROLYTIC 4.7uF 50V
C611,C612 12005280 CAPACITOR ELECTROLYTIC 47uF 50V
C613,C614 12001410 CAPACITOR STYROL 47pF 125V
C615,C616 12001285 CAPACITOR MYLAR 0.1uF 100V
C617,C618 12001420 CAPACITOR STYROL 22pF 125V
C711,C712 12005090 CAPACITOR ELECTROLYTIC 10uF 25V
C713,C714 12002070 CAPACITOR CERAMIC 0.01uF 50V
C715,C716 12005040 CAPACITOR ELECTROLYTIC 22uF 50V
C717,C718 12005080 CAPACITOR ELECTROLYTIC 100uF 16V
D601-D604 16000082 DIODE RD8.2JS-T1
D607-D616 16000082 DIODE RD8.2JS-T1
D711,D712 16004003 DIODE 1N4003
F601-F604 19000500 FUSE 5A 250V
IC711, IC712 21005550 TIMER IC NJM555D
Q601-Q604 33002100 TRANSISTOR IRFD210
Q605,Q606 33000610 TRANSISTOR IRF610
Q607,Q608 33009210 TRANSISTOR IRFD9210

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