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: 732-683-2356
Fax: 732-683-9790
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. DO NOT ATTEMPT FAMILIARIZATION,
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. THESE INSTRUCTIONS ARE
PROVIDED FOR USE ONLY BY COMPETENT TECHNICAL PERSONNEL. DO NOT UNDERTAKE
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.
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. 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 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
1
2
3
4
Coupling
Plus Lead Minus Lead
R675
R675
R676
R676
L SPKR +
L SPKR R SPKR +
R SPKR -
a
GFA-5400 SERVICE PARTS LIST
Adjust
Adjust For
VR603
VR604
VR601
VR602
DC Voltmeter
reads 35mV
DC Voltmeter
reads 0mV
Power Supply PCB
AF608615
SCHEMATIC
LOCATION
C901-C904
C905-C908
C909-C912
C913-C916
C917-C920
D903-D914
R901-R904
R905-R912
R913-R916
TH901, TH902
ADCOM PART NUMBER
DESCRIPTION
12005565
12001185
12005420
12005195
12001185
16004003
27001590
27005030
27003280
31000512
CAPACITOR ELECTROLYTIC
CAPACITOR MP
CAPACITOR ELECTROLYTIC
CAPACITOR ELECTROLYTIC
CAPACITOR MP
DIODE
RESISTOR
RESISTOR ROED.
RESISTOR ROED.
THERMISTOR
12000uF 63V
0.1uF 250V
1000uF 16V
470uF 100V
0.1uF 250V
1N4003
5.6K 1W MOF
10 1/2W FUSABLE
8.2K 2W 5% METAL
SCK0512
Amplifier PCB
AF608625, AF608635
SCHEMATIC
LOCATION
C601,C602
C603,C604
C605,C606
C607,C608
C609,C610
C611,C612
C613,C614
C615,C616
C617,C618
C711,C712
C713,C714
C715,C716
C717,C718
D601-D604
D607-D616
D711,D712
F601-F604
IC711, IC712
Q601-Q604
Q605,Q606
Q607,Q608
ADCOM PART NUMBER
DESCRIPTION
12003175
12001260
12005470
12001020
12005325
12005280
12001410
12001285
12001420
12005090
12002070
12005040
12005080
16000082
16000082
16004003
19000500
21005550
33002100
33000610
33009210
CAPACITOR STYROL
CAPACITOR MP
CAPACITOR ELECTROLYTIC
CAPACITOR LAYER
CAPACITOR ELECTROLYTIC
CAPACITOR ELECTROLYTIC
CAPACITOR STYROL
CAPACITOR MYLAR
CAPACITOR STYROL
CAPACITOR ELECTROLYTIC
CAPACITOR CERAMIC
CAPACITOR ELECTROLYTIC
CAPACITOR ELECTROLYTIC
DIODE
DIODE
DIODE
FUSE
TIMER IC
TRANSISTOR
TRANSISTOR
TRANSISTOR
2
390pF 125V
2.2uF 100V
47uF 100V
1uF 50V
4.7uF 50V
47uF 50V
47pF 125V
0.1uF 100V
22pF 125V
10uF 25V
0.01uF 50V
22uF 50V
100uF 16V
RD8.2JS-T1
RD8.2JS-T1
1N4003
5A 250V
NJM555D
IRFD210
IRF610
IRFD9210
SCHEMATIC
LOCATION
Q609,Q610
Q611,Q612
Q613,Q614
Q615-Q620
Q621-Q626
Q627-Q630
Q631-Q634
Q635-Q638
Q711,Q712
Q713,Q714
Q715,Q716
Q717,Q718
R601,R602
R603-R606
R607-R610
R611,R612
R613,R614
R617,R618
R619, R620
R623,R624
R625,R626
R627-R630
R631-R634
R635,R636
R637,R638
R639-R642
R643,R644
R645,R646
R647-R650
R651-R654
R655-R670
R671,R672
R673,R674
R675-R686
R687,R688
R691,R692
R693-R696
R711,R712
R713,R714
R715,R716
R717,R718
R719,R720
R721,R722
R723,R724
R725,R726
R729,R730
S601, S602
VR601-VR604
ADCOM PART NUMBER
DESCRIPTION
33009610
33002100
33000610
33002400 *(See Note 1)
33000924 *(See Note 1)
33001016
33002362
33001016
33002274
33003478
33001016
33003478
27001565
27002480
27004061
27002240
27002025
27002170
27002030
27002030
27004290
27001565
27001565
27004061
27001515
27002010
27001530
27002030
27002410
27001520
27001565
27002095
27001590
27003155
27004475
27002020
27002010
27002030
27002095
27001090
27002020
27002200
27002440
27002365
27001530
27002150
32005400
35001225
POWER TRANSISTOR
TRANSISTOR
POWER TRANSISTOR
POWER TRANSISTOR
POWER TRANSISTOR
TRANSISTOR
TRANSISTOR
TRANSISTOR
TRANSISTOR
TRANSISTOR
TRANSISTOR
TRANSISTOR
RESISTOR ROED.
RESISTOR ROED.
RESISTOR ROED.
RESISTOR ROED.
RESISTOR ROED.
RESISTOR ROED.
RESISTOR ROED.
RESISTOR ROED.
RESISTOR ROED.
RESISTOR ROED.
RESISTOR ROED.
RESISTOR ROED.
RESISTOR ROED.
RESISTOR ROED.
RESISTOR ROED.
RESISTOR ROED.
RESISTOR ROED.
RESISTOR ROED.
RESISTOR ROED.
RESISTOR ROED.
RESISTOR
RESISTOR
RESISTOR
RESISTOR ROED.
RESISTOR ROED.
RESISTOR ROED.
RESISTOR ROED.
RESISTOR
RESISTOR ROED.
RESISTOR ROED.
RESISTOR ROED.
RESISTOR ROED.
RESISTOR ROED.
RESISTOR ROED.
THERMAL BREAKER (85°C)
POTENTIOMETER
3
IRF9610
IRFD210
IRF610
IRFP240
IRFP9240
2SA1016G
2SC2362F
2SA1016G
2SC2274E
2SC3478T
2SA1016G
2SC3478T
221 1/4W 1%
1.82K 1/4W 1%
51K 1/4W 1%
7.5K 1/4W 1%
1.54K 1/4W 1%
470 1/4W 1%
10K 1/4W 1%
10K 1/4W 1%
18.2K 1/4W 1%
221 1/4W 1%
221 1/4W 1%
51K 1/4W 1%
4.75 1/4W 1%
100 1/4W 1%
2.74K 1/4W 1%
10K 1/4W 1%
4.7K
68
221
2.21K
5.6K 1W MOF
0.56 3W MOF
5.6 2W MOF
1K 1/4W 1%
100 1/4W 1%
10K 1/4W 1%
2.21K 1/4W 1%
220K 5%
1K 1/4W 1%
4.99K 1/4W 1%
33.2K 1/4W 1%
49.9K 1/4W 1%
2.74K 1/4W 1%
3.32K 1/4W 1%
BOARD MOUNT 4.7K
Power Switch PCB
AF608645
SCHEMATIC
LOCATION
C921
C922
C922
PW901
TH903
ADCOM PART NUMBER
DESCRIPTION
12005700
12001605
12001615
37001325
31002512
SPARK KILLER 4700pF
MOV (120V operation)
MOV (240V operation)
POWER SWITCH
THERMISTOR
KC472M
TNR12G241K
TNR12G431K
SCK2R512
Protection Circuit Power Supply PCB
AF608665
SCHEMATIC
LOCATION
C701
C702
D701
F701
IC701
TT002
ADCOM PART NUMBER
DESCRIPTION
12005070
12005120
16001530
19000100
21007800
24005002
CAPACITOR ELECTROLYTIC
CAPACITOR ELECTROLYTIC
BRIDGE
FUSE
REGULATOR IC
STANDBY TRANSFORMER
ADCOM PART NUMBER
DESCRIPTION
16001540
19000800
19000400
20005200
16001204
16001204
16001254
11001155
11001040
11001165
11001170
15001050
15001150
13005403
24005401
22001170
13005400
13001020
30005800
13005401
BRIDGE RECTIFIER
FUSE (120VAC operation)
FUSE (240VAC operation)
FUSE HOLDER
THERMAL LED (Red)
POWER LED (Red)
DISTORTION LED (Yellow)
PLASTIC POWER BUTTON
BUTTON SPRING
BUTTON MOUNTING RING
CLEAR BUTTON INSERT
POWER CORD
CORD STOPPER
PRINTED REAR CHASSIS
POWER TRANS. (VER. 2)
INPUT JACK (VER. 2)
TOP COVER
FOOT
SPEAKER POST (VER. 2)
FRONT PANEL
1000uF 35V
220uF 16V
1A 250V
NJM7812A
Other Hardware
SCHEMATIC
LOCATION
D901,D902
F001
F001
D001, D002
4
MP154
8A 250V
4A 250V
LTL-1204A
LTL-1204A
LTL-1254A
PARTS EXCLUSIVE TO VERSION ONE OF THE GFA-5400
(VERSION WITHOUT STANDBY POWER SUPPLY AND LM 555 PROTECTION CIRCUITRY)
SCHEMATIC
LOCATION
D605,D606
R615,R616
R621,R622
PJ1,PJ2
Q639,Q640
T1
ADCOM PART NUMBER
DESCRIPTION
16000082
27004300
27004200
22001370
30001045
30001035
33002362
24005400
DIODE
RESISTOR
RESISTOR
INPUT JACK, Board Mount
SPEAKER POST RED
SPEAKER POST BLACK
TRANSISTOR
POWER TRANSFORMER
8.2V ZENER
15K
10K
2SC2362
* Note 1: Matched IRFP240 and IRFP9240. Due to manufacturing variations in the turn on voltage of
these devices, these parts must be replaced in matched sets of 3. If any one of the output devices fails,
all three must be replaced. For example, if Q616 fails in the right channel, then all 3 of the N-channel
IRFP240 devices must be replaced in that channel (Q616, Q618, Q620). When ordering these parts,
specify a matched set of 3. Failure to use matched devices will cause "current hogging" by one of the
output devices. Proper bias alignment will not be possible in this circumstance leading to incorrect and,
possibly, unreliable operation.
5
a GFA-5400 SPECIFICATIONS
Power Rating (To FTC 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 0.18% THD
200 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 125 watts into 8 ohms ............................................................................................................................. ≤ 0.05%
1 watt to 200 watts into 4 ohms ............................................................................................................................. ≤ 0.05%
IM Distortion (CCIF, Any Combination from 4kHz to 20kHz)
125 watts into 8 ohms .......................................................................................................................................... ≤ 0.035%
200 watts into 4 ohms .......................................................................................................................................... ≤ 0.035%
THD + Noise at 130 watts into 8 ohms (Typical)
20Hz ....................................................................................................................................................................... 0.018%
1kHz ......................................................................................................................................................................... 0.02%
10kHz ....................................................................................................................................................................... 0.07%
20kHz ....................................................................................................................................................................... 0.14%
THD + Noise at 200 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 ...................................................................................................................................... 1.7 dB
Signal to Noise Ratio, “A” Weighted (125 watts into 8 ohms)...................................................................................... ≥ 100dB
Gain...... ................................................................................................................................................................................. 29dB
Input Sensitivity
for 1 Watt .............................................................................................................................................................. 0.1 volts
for 125 Watts ..................................................................................................................................................... 1.125 volts
Input Impedance................................................................................................................................................................ 49.9KΩ
Damping Factor (20Hz to 20kHz) ........................................................................................................................................ ≥ 500
Rise Time (5kHz, 90V, peak-to-peak square wave, 20% to 80%) .................................................................................... . 1.9µS
Power Consumption (Continuous, All Channels Driven)
Quiescent ................................................................................................................................................................
Maximum .................................................................................................................................................................
125 watts into 8 ohms ..............................................................................................................................................
200 watts into 4 ohms ..............................................................................................................................................
150VA
960VA
580VA
920VA
Power (Available in 230VAC on special order) ................................................................................................. 115VAC - 50/60Hz
Chassis Dimensions ............................................................................................... 5” (127mm) x 17” (432mm) x 11.5” (292mm)
Maximum Dimensions ......................................................................................... 53/8” (137mm) x 17” (432mm) x 12.5” (375mm)
Weight.. ................................................................................................................................................................... 26 lb. (11.8 kg)
Weight, Packed........................................................................................................................................................ 30 lb. (13.6kg)
6