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

2

SCHEMATIC ADCOM PART NUMBER DESCRIPTION
LOCATION

Q609,Q610 33009610 POWER TRANSISTOR IRF9610
Q611,Q612 33002100 TRANSISTOR IRFD210
Q613,Q614 33000610 POWER TRANSISTOR IRF610
Q615-Q620 33002400 *(See Note 1) POWER TRANSISTOR IRFP240
Q621-Q626 33000924 *(See Note 1) POWER TRANSISTOR IRFP9240
Q627-Q630 33001016 TRANSISTOR 2SA1016G
Q631-Q634 33002362 TRANSISTOR 2SC2362F
Q635-Q638 33001016 TRANSISTOR 2SA1016G
Q711,Q712 33002274 TRANSISTOR 2SC2274E
Q713,Q714 33003478 TRANSISTOR 2SC3478T
Q715,Q716 33001016 TRANSISTOR 2SA1016G
Q717,Q718 33003478 TRANSISTOR 2SC3478T
R601,R602 27001565 RESISTOR ROED. 221 1/4W 1%
R603-R606 27002480 RESISTOR ROED. 1.82K 1/4W 1%
R607-R610 27004061 RESISTOR ROED. 51K 1/4W 1%
R611,R612 27002240 RESISTOR ROED. 7.5K 1/4W 1%
R613,R614 27002025 RESISTOR ROED. 1.54K 1/4W 1%
R617,R618 27002170 RESISTOR ROED. 470 1/4W 1%
R619, R620 27002030 RESISTOR ROED. 10K 1/4W 1%
R623,R624 27002030 RESISTOR ROED. 10K 1/4W 1%
R625,R626 27004290 RESISTOR ROED. 18.2K 1/4W 1%
R627-R630 27001565 RESISTOR ROED. 221 1/4W 1%
R631-R634 27001565 RESISTOR ROED. 221 1/4W 1%
R635,R636 27004061 RESISTOR ROED. 51K 1/4W 1%
R637,R638 27001515 RESISTOR ROED. 4.75 1/4W 1%
R639-R642 27002010 RESISTOR ROED. 100 1/4W 1%
R643,R644 27001530 RESISTOR ROED. 2.74K 1/4W 1%
R645,R646 27002030 RESISTOR ROED. 10K 1/4W 1%
R647-R650 27002410 RESISTOR ROED. 4.7K
R651-R654 27001520 RESISTOR ROED. 68
R655-R670 27001565 RESISTOR ROED. 221
R671,R672 27002095 RESISTOR ROED. 2.21K
R673,R674 27001590 RESISTOR 5.6K 1W MOF
R675-R686 27003155 RESISTOR 0.56 3W MOF
R687,R688 27004475 RESISTOR 5.6 2W MOF
R691,R692 27002020 RESISTOR ROED. 1K 1/4W 1%
R693-R696 27002010 RESISTOR ROED. 100 1/4W 1%
R711,R712 27002030 RESISTOR ROED. 10K 1/4W 1%
R713,R714 27002095 RESISTOR ROED. 2.21K 1/4W 1%
R715,R716 27001090 RESISTOR 220K 5%
R717,R718 27002020 RESISTOR ROED. 1K 1/4W 1%
R719,R720 27002200 RESISTOR ROED. 4.99K 1/4W 1%
R721,R722 27002440 RESISTOR ROED. 33.2K 1/4W 1%
R723,R724 27002365 RESISTOR ROED. 49.9K 1/4W 1%
R725,R726 27001530 RESISTOR ROED. 2.74K 1/4W 1%
R729,R730 27002150 RESISTOR ROED. 3.32K 1/4W 1%
S601, S602 32005400

THERMAL BREAKER (85°C)

VR601-VR604 35001225 POTENTIOMETER BOARD MOUNT 4.7K

3

Power Switch PCB
AF608645

SCHEMATIC ADCOM PART NUMBER DESCRIPTION
LOCATION

C921 12005700 SPARK KILLER 4700pF KC472M
C922 12001605 MOV (120V operation) TNR12G241K
C922 12001615 MOV (240V operation) TNR12G431K
PW901 37001325 POWER SWITCH
TH903 31002512 THERMISTOR SCK2R512

Protection Circuit Power Supply PCB
AF608665

SCHEMATIC ADCOM PART NUMBER DESCRIPTION
LOCATION

C701 12005070 CAPACITOR ELECTROLYTIC 1000uF 35V
C702 12005120 CAPACITOR ELECTROLYTIC 220uF 16V
D701 16001530 BRIDGE
F701 19000100 FUSE 1A 250V
IC701 21007800 REGULATOR IC NJM7812A
TT002 24005002 STANDBY TRANSFORMER

Other Hardware

SCHEMATIC ADCOM PART NUMBER DESCRIPTION
LOCATION

D901,D902 16001540 BRIDGE RECTIFIER MP154
F001 19000800 FUSE (120VAC operation) 8A 250V
F001 19000400 FUSE (240VAC operation) 4A 250V

20005200 FUSE HOLDER

D001, D002 16001204 THERMAL LED (Red) LTL-1204A

16001204 POWER LED (Red) LTL-1204A
16001254 DISTORTION LED (Yellow) LTL-1254A
11001155 PLASTIC POWER BUTTON
11001040 BUTTON SPRING
11001165 BUTTON MOUNTING RING
11001170 CLEAR BUTTON INSERT
15001050 POWER CORD
15001150 CORD STOPPER
13005403 PRINTED REAR CHASSIS
24005401 POWER TRANS. (VER. 2)
22001170 INPUT JACK (VER. 2)
13005400 TOP COVER
13001020 FOOT
30005800 SPEAKER POST (VER. 2)
13005401 FRONT PANEL

4

PARTS EXCLUSIVE TO VERSION ONE OF THE GFA-5400

(VERSION WITHOUT STANDBY POWER SUPPLY AND LM 555 PROTECTION CIRCUITRY)

SCHEMATIC ADCOM PART NUMBER DESCRIPTION
LOCATION

D605,D606 16000082 DIODE 8.2V ZENER
R615,R616 27004300 RESISTOR 15K
R621,R622 27004200 RESISTOR 10K
PJ1,PJ2 22001370 INPUT JACK, Board Mount

30001045 SPEAKER POST RED

30001035 SPEAKER POST BLACK
Q639,Q640 33002362 TRANSISTOR 2SC2362
T1 24005400 POWER TRANSFORMER

* 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

a

aa

Power Rating (To FTC Requirements)

IM Distortion (SMPTE)

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

THD + Noise at 130 watts into 8 ohms (Typical)

THD + Noise at 200 watts into 4 ohms (Typical)

GFA-5400 SPECIFICATIONS

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

1 watt to 125 watts into 8 ohms ............................................................................................................................. ≤ 0.05%

1 watt to 200 watts into 4 ohms ............................................................................................................................. ≤ 0.05%

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

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

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

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

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

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

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

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

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

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

Frequency Response @ 1 Watt into 8 ohms (10Hz to 20kHz)

Power Bandwidth (-3dB)

Dynamic Headroom into 4 ohms

Signal to Noise Ratio, “A” Weighted (125 watts into 8 ohms)

Gain

....................................................................................................................................................................................... 29dB

Input Sensitivity

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

for 125 Watts ..................................................................................................................................................... 1.125 volts

Input Impedance

Damping Factor (20Hz to 20kHz)

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

Power Consumption (Continuous, All Channels Driven)

Quiescent ................................................................................................................................................................ 150VA

Maximum................................................................................................................................................................. 960VA

125 watts into 8 ohms.............................................................................................................................................. 580VA

200 watts into 4 ohms.............................................................................................................................................. 920VA

................................................................................................................................................................ 49.9K

....................................................................................................................................... 3Hz to 130kHz

...................................................................................................................................... 1.7 dB

........................................................................................................................................ ≥ 500

................................................................................ +0, -0.25dB

...................................................................................... ≥ 100dB

.................................................................................... . 1.9µS

Ω

Power

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

Chassis Dimensions
Maximum Dimensions

Weight

.....................................................................................................................................................................26 lb. (11.8 kg)

Weight, Packed

............................................................................................... 5” (127mm) x 17” (432mm) x 11.5” (292mm)

......................................................................................... 5

........................................................................................................................................................30 lb. (13.6kg)

3

/8” (137mm) x 17” (432mm) x 12.5” (375mm)

6