Adcom gfa 7807 service manual

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adcom gfa 7807 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-7807 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. Initial bias of individual modules shuld be adjusted to 3mv across the 0.2 ohm emitter resistors. Recheck module bias when amp modules are in the chassis and warm. - Insert a 0.1 ohm resistor in the top fuse location F2 ( Note: I did this by taking 2 each 0.2 ohm emitter resistors in parallel and soldered to a burnt fuse. ) - Measure voltage across the 0.1 ohm resistor -¦ check and adjust ( VR1) bias to 10 mV or 100 mA at this point. NOTE: The bias adjustment must be performed with the heatsink attached and the amplifier module installed in the chassis. 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-7807 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-7807 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-7807 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-7807 SERVICE PARTS LIST AMPLIFIER MODULE PCB SCHEMATIC ADCOM PART NUMBER DESCRIPTION LOCATION BR1, BR2 16007000 BRIDGE RECTIFIER KBU8J C01 ,C04 ,C13 12005090 CAPACITOR ELEC 10uF 25V C02 ,C03 ,C14 ,C15 12007800 CAPACITOR ELEC 5600uF 100V C05 ,C09 12006030 CAPACITOR ELEC 0.1uF 50V C06 ,C17 ,C23 12005220 CAPACITOR ELEC 100uF 10V C07 12007801 CAPACITOR POLYPROPYLENE 6800pF 63V C08 12005380 CAPACITOR ELEC 47uF 25V C10 12001555 CAPACITOR POLY 100nF 250V C11 12001700 CAPACITOR SIVLER MICA 7pF 500V C12 12001365 CAPACITOR ELEC 47pF 500V C16 ,C20 12001085 CAPACITOR POLY 0.22uF 50V C18 ,C19 12005225 CAPACITOR ELEC 100uF 100V C21 ,C22 12007802 CAPACITOR POLYPROPYLENE 330pF 100V D01 ,D07 16007800 DIODE ZENER 15V 1/2W 1N965B D02 ,D04 ,D08 ,D09 ,D10 16004148 DIODE 1N4148 D03-D06 16004004 DIODE 1N4007 U01 ,U04 21004250 IC 4N25N U02 21005550 IC NE555N U03 IC H11AA814 U05 21000071 IC TL071 F1 ,F2 19009800 FUSE T6.3A K1 28007400 RELAY G4A-1A-PE Q01 33001380 TRANSISTOR 2SA1380 Q02 ,Q09 ,Q23 ,Q24 Q26 ,Q28 33003904 TRANSISTOR 2N3904 Q03 33004793 TRANSISTOR 2SC4793 Q04 ,Q12 ,Q13 33005401 TRANSISTOR 2N5401 Q05 ,Q06 ,Q07 ,Q08 ,Q11 33005200 TRANSISTOR KSC5200 Q10 33001567 TRANSISTOR 2SC1567A Q14 ,Q15 ,Q16 ,Q17 ,Q22 33001943 TRANSISTOR KSA1943 Q18 33001873 TRANSISTOR 2SA1837 Q19 33003502 TRANSISTOR 2SC3502 Q20 33000600 TRANSISTOR MPSA06 Q21 33000042 TRANSISTOR MPSA42 Q27 TRANSISTOR 2N3906 R01 ,R43 27004050 RESISTOR 1K R02 ,R45 ,R56 ,R57 27003055 RESISTOR 10K 2W 5% R03 ,R19 27004070 RESISTOR 2K21 R04 27004120 RESISTOR 22K1 R05 27004670 RESISTOR 100 R06 ,R35 ,R38 27001565 RESISTOR 221 R07 ,R14 ,R24 ,R36 ,R39 ,R40 ,R63 27002410 RESISTOR 4.75K SCHEMATIC ADCOM PART NUMBER DESCRIPTION R08 ,R13 ,R22 ,R37 27004210 RESISTOR 100K