BASS AMPLIFIER SERVICE MANUAL This document is printed on chlorine free (ECF) paper with soy ink. CONTENTS SPECIFICATIONS .............................................................................. PANEL LAYOUT .................................................................................. CIRCUIT BOARD LAYOUT ................................................................. BLOCK DIAGRAM .............................................................................. DISASSEMBLY PROCEDURE ..........
F-20B IMPORTANT NOTICE This manual has been provided for the use of authorized Yamaha Retailers and their service personnel. It has been assumed that basic service procedures inherent to the industry, and more specifically Yamaha Products, are already known and understood by the users, and have therefore not been restated.
F-20B SPECIFICATIONS Rated Output Power: Speaker: Controls: 20W 25cm x 1 VOLUME, TREBLE, HIGH MID, LOW MID, BASS, Input Level Select Switch (PASSIVE/ACTIVE) Input/Output Terminals: INPUT, AUX IN, PHONES Power Consumption: 25W/120V (UL, CSA) 25W/230V (E, BS) Power Requirements: U.S. and Canadian models: 120V, 60Hz General model: 230V, 50Hz Dimensions (W x H x D) : 357 x 453 x 242mm (14.1" x 17.8" x 9.5") Weight: 10.
F-20B CIRCUIT BOARD LAYOUT Top Side View View AC Cord MAIN 2/2 Power Transformer MAIN 2/2 MAIN 1/2 MAIN 1/2 Front View MAIN 1/2 BLOCK DIAGRAM MAIN 1/2 GAIN SELECT ACTIVE CH. PASSIVE CH.
F-20B DISASSEMBLY PROCEDURE 1. 1-1 1-2 1-3 Pre-Main Unit (Time required: about 2 min) Remove the eight (8) screws marked [A]. The back board can then be removed. (Fig.1) Pull out the speaker wires. (Fig.1) Remove the four (4) screws marked [30]. The premain unit can then be removed by sliding it backward. (Fig.1) 2. 2-1 2-2 2-3 Speaker (Time required: about 2 min) Remove the back board. (See Procedure 1-1) Pull out the speaker wires. (Fig.1) Remove the four (4) screws marked [60a].
F-20B 4. 4-1 4-2 5. 5-1 5-2 MAIN 2/2 Circuit Board (Time required: about 3 min) Remove the pre-main unit. (See Procedure 1) Remove the screw marked [C80]. The MAIN 2/2 circuit board can then be removed. (Fig.3, Fig.5) Power Transformer (Time required: about 4 min) Remove the pre-main unit. (See Procedure 1) While holding the nuts marked [P70] with a spanner, remove the two (2) screws marked [P60]. The power transformer can then be removed. (Fig.
F-20B A CIRCUIT BOARDS MAIN1/2 INPUT CIRCUIT BOARD GAIN SELECT VOLUME TREBLE A' A to POWER TRANSFORMER to MAIN 2/2 CN4 from POWER TRANSFORMER to POWER SW from AC CORD VERSION FUSE RATE J, U 250V 315mAL E, BS 250V T160mAL INDICATION Must be erased Must be erased POWER HIGH MID LOW MID BASS AUX IN PHONES to SPEAKER Component side A' MAIN 1/2 (J, U, C): MAIN 1/2 (H, B): MAIN 2/2 (J, U, C): MAIN 2/2 (H, B): MAIN2/2 CNA-V755470 CNA-V755480 CNA-V755470 CNA-V755480 CIRCUIT BOARD to
F-20B IC BLOCK DIAGRAM BA4558 (XO078A00) Dual Operational Amplifier MAIN: IC1,IC2,IC3 Output A 1 Inverting Input A 2 Non-Inverting Input A 3 -DC Voltage Supply 4 +V - + + -V - 8 +DC Voltage Supply 7 Output B 6 Inverting Input B 5 Non-Inverting Input B INSPECTIONS 1. Preparation To inspect the main unit, the following jigs are required. CD player Headphones Before turning the power on, set all the knobs on the panel to "0".
F-20B BASS AMPLIFIER PARTS LIST CONTENS OVERALL ASSEMBLY .................................................................................. 2 PRE-MAIN UNIT ............................................................................................ 4 ELECTRICAL PARTS ....................................................................................
F-20B OVERALL ASSEMBLY 20 Pre-Main Unit 50 30 40 C60 C50 C40 C60 C50 C30 60a C20 60 C30 C100 C110 A C70 C90 C80 10 Overall Cabinet Assembly 2
F-20B 10 20 20 20 20 30 40 50 50 50 60 60a ----V 7 4 6 11 0 0 ----VN347600 ET500040 ---XO361A00 VB403600 DESCRIPTION OVERALL ASSEMBLY Overall Assembly Overall Assembly Overall Assembly Overall Assembly Overall Cabinet Assembly Pre-Main Unit Pre-Main Unit Pre-Main Unit Pre-Main Unit Truss Head Screw Flat Washer Label Label Label Speaker Unit Bind Head Screw C10 C20 C30 C40 C50 C60 C70 C80 C90 C100 C110 A V 7 4 6 11 0 0 -V5969000 21770200 V6327200 V6327300 V7017900 V6327400 EP030310 03765580 V7363300 VN7
F-20B PRE-MAIN UNIT A100 A120 A110 A10 A70 A40 A140 A130 A60 A50 P80 A30 A80 A10 A90 A20 P20 P50 P75 P70 P30 Amp Kit P10 P90 P60 P77 P100 P40 P60 P120 4 P110
F-20B REF NO. * P10 P20 P30 P30 P30 P30 P40 P50 P60 P70 P75 P77 P80 P90 P100 PART NO.
F-20B ELECTRICAL PARTS REF NO.
F-20B REF NO. * * * * * R16 R17 -19 R20 R21 R22 R23 R24 R25 R26 R27 R28 R29 R30 R31 R32 SW2 VR1 VR2 VR3 VR4 VR5 ZD1 ZD2 PART NO.
A B C D E F G H
OVERALL CIRCUIT DIAGRAM F-20B D2SBA20 (VP344100) DIODE STACK 1.5A 200V MAIN 1/2 1 DB1 GAIN SELECT OP AMP OP AMP OP AMP OP AMP OP AMP 2 AUX IN INPUT BASS LOW MID HIGH MID TREBLE MAIN 2/2 OP AMP 3 OP AMP VOLUME HIFI AMP POWER ON/OFF KEC-54238 OP AMP J, U, C PHONES S, BS 250V 315mA 250V T160mA L 4 4 SPEAKER TRANS FORMER KEC-54238 5 WARNING Note: See parts list for details of circuit board component parts.