Adcom GFA-7605 free download

File name hfe_adcom_gfa-7605_service.pdf

SERVICE MANUAL 5 CHANNEL POWER AMPLIFIER GFA-7605 TABLE OF CONTENTS Introduction . . . . . . . . . . . . . . . . 1 Test Procedures . . . . . . . . . . . . . 1 Parts List . . . . . . . . . . . . . . . . . . 2 Voltage Conversion . . . . . . . . . . . . 5 Specifications . . . . . . . . . . . . . . . 7 PCB Layouts. . . . . . . . . . . . . . . . . . 8 Schematic . . . . . . . . . . . . . . . . . 9 8551 East Anderson Drive,Suite 105 Scottsdale, Arizona 85255 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-7605 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-7605 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-7605 FROM THE WALL AC OUTLET OR OTHER SOURCE OF AC POWER AND THE POWER- SUPPLY CAPACITORS ARE COMPLETELY DISCHARGED. THESE INSTRUCTIONS ARE PROVIDED FOR USE ONLY BY COMPETENT TECHNICAL PERSONNEL. DO NOT UNDERTAKE ANY SERVICE PROCEDURES IN THE GFA-7605 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 The component references are the same for all channels. Operate the amplifier without load or input connection for this adjustment. 1. Turn the amplifier on and allow to idle for 5 minutes. 2. Connect millivoltmeter across emitter resistor R36. Adjust bias pot R25 for a 10m