Adcom gfa 7605 service manual

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adcom gfa 7605 service manual

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1 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. 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. 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 10mV +/- 1mV reading. NOTE: The bias adjustment must be performed with the heatsink attached and the amplifier module installed in the chassis. The best way to perform the bias adjustment is by connecting one probe of millivoltmeter to emitter of Q15 (lowest pin) and connecting the other probe to the positive (red) speaker output. DC OFFSET CHECK 1. Connect a millivoltmeter across the speaker output terminals and confirm a reading of 0mV +/- 10mV. 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. IMPORTANT BEFORE PROCEEDING WITH ADJUSTMENTS, MAKE SURE AMPLIFIER IS AT ROOM TEMPERATURE.

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2 GFA-7605 SERVICE PARTS LIST AMPLIFIER MODULE PCB SCHEMATIC ADCOM PART NUMBER DESCRIPTION LOCATION BR2 BRIDGE RECTIFIER SBU8G C01 CAPACITOR POLY FILM 2.2uF 100V C02 CAPACITOR POLY FILM 330pF 100V C03 CAPACITOR ELEC 100uF 63V C04 CAPACITOR MYLAR FILM 1uF 100V C05 CAPACITOR SILVER MICA 33pF 100V C06 CAPACITOR POLY FILM 4.7nF 100V C07 CAPACITOR ELEC 10uF 25V C08 CAPACITOR ELEC 100uF 100V C09 CAPACITOR ELEC 100uF 100V C10 CAPACITOR POLY 270pF 100V C11 CAPACITOR POLY 270pF 100V C12 CAPACITOR ELEC 100uF 10V C13 CAPACITOR MYLAR 0.1uF 250V C15 CAPACITOR ELEC 10uF 25V C16 CAPACITOR POLY 0.01uF 100V C17 CAPACITOR ELEC 22uF 35V C18 CAPACITOR ELEC 10000uF 63WV C19 CAPACITOR ELEC 10000uF 63WV C20 CAPACITOR MYLAR 0.22uF C21 CAPACITOR MYLAR 0.22uF C22 CAPACITOR ELEC 100uF 16V C23 CAPACITOR ELEC 220uF 25V D02-D05 DIODE 1N4148 D08,D09 DIODE 1N4007 D10-D13 DIODE 1N4148 F3 FUSE T6.3A F4 FUSE T6.3A J1 RCA INPUT JACK LED1 DISTORTION LED LTL1254 (YELLOW) LED2 PROTECT LED LTL1204 (RED) Q01 TRANSISTOR 2SC3381 Q02 TRANSISTOR MPSA92 Q03 TRANSISTOR MPSA42 Q04 TRANSISTOR MPSA92 Q05 TRANSISTOR MPSA92 Q06 TRANSISTOR MPSA92 Q07 TRANSISTOR 2SA1380 Q08 TRANSISTOR 2SC3502F Q09 TRANSISTOR 2SC1567 Q10 TRANSISTOR 2SC4793 Q11 TRANSISTOR 2SA1837 Q12 TRANSISTOR 2SC3281 Q13 TRANSISTOR 2SA1302 Q14 TRANSISTOR 2SC3281 Q15 TRANSISTOR 2SA1302 Q16 TRANSISTOR MPSA42 Q17 TRANSISTOR MPSA42 Q18 TRANSISTOR MPSA42