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GUITAR AMPLIFIER
SERVICE MANUAL
CONTENTS |
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SPECIFICATIONS .............................................................................. |
3 |
PANEL LAYOUT .................................................................................. |
3 |
CIRCUIT BOARD LAYOUT ................................................................. |
4 |
BLOCK DIAGRAM .............................................................................. |
4 |
DISASSEMBLY PROCEDURE ........................................................... |
5 |
CIRCUIT BOARDS ............................................................................. |
7 |
IC BLOCK DIAGRAM.......................................................................... |
8 |
INSPECTIONS .................................................................................... |
8 |
PARTS LIST |
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OVERALL CIRCUIT DIAGRAM |
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This document is printed on chlorine free (ECF) paper with soy ink.
GA 011551
HAMAMATSU, JAPAN
1.338K-713 K 
Printed in Japan 2001.09
F-20
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.
WARNING:
IMPORTANT:
Failure to follow appropriate service and safety procedures when servicing this product may result in personal injury, destruction of expensive components and failure of the product to per form as specified. For these reasons, we advise all Yamaha product owners that all service required should be performed by an authorized Yamaha Retailer or the appointed service representative.
This presentation or sale of this manual to any individual or firm does not constitute authorization, certification, recognition of any applicable technical capabilities, or establish a principal-agent relationship of any form.
The data provided is believed to be accurate and applicable to the unit(s) indicated on the cover. The research engineering, and service departments of Yamaha are continually striving to improve Yamaha products. Modifications are, therefor, inevitable and changes in specification are subject to change without notice or obligation to retrofit. Should any discrepancy appear to exist, please contact the distributor's Service Division.
WARNING:
IMPORTANT:
Static discharges can destroy expensive components. Discharge any static electricity your body may have accumulated by grounding yourself to the ground buss in the unit (heavy gauge black wires connect to this buss).
Turn the unit OFF during disassembly and parts replacement. Recheck all work before you apply power to the unit.
WARNING: CHEMICAL CONTENT NOTICE!
The solder used in the production of this product contains LEAD. In addition, other electrical / electronic and / or plastic (where applicable) components may also contain traces of chemicals found by the California Health and Welfare Agency (and possibly other entities) to cause cancer and / or birth defects or other reproductive harm.
DO NOT PLACE SOLDER, ELECTRICAL / ELECTRONIC OR PLASTIC COMPONENTS IN YOUR MOUTH FOR ANY REASON WHAT SO EVER!
Avoid prolonged, unprotected contact between solder and your skin! When soldering, do not inhale solder fumes or expose eyes to solder / flux vapor!
If you come in contact with solder or components located inside the enclosure of this product, wash your hands before handling food.
IMPORTANT NOTICE FOR THE UNITED KINGDOM
Connecting the Plug and Cord
WARNING: THIS APPARATUS MUST BE EARTHED
IMPORTANT: The wires in this main lead are coloured in accordance with the following code: GREEN-AND-YELLOW: EARTH
BLUE: NEUTRAL
BROWN: LIVE
As the colours of the wires in the main lead of this apparatus may not correspond with the coloured markings identifying the terminals in your plug, proceed as follows:
The GREEN-and-YELLOW wire must be connected to the terminal in the plug that is marked with the letter E or the safety earth symbol (or coloured GREEN or GREEN-and-YELLOW).
The BLUE wire must be connected to the terminal that is marked with the letter N (or coloured BLACK).
The BROWN wire must be connected to the terminal that is marked with the letter L (or coloured RED).
This applies only to products distributed by Yamaha Kemble Music (U. K.) Ltd.
WARNING
Components having special characteristics are marked 
and must be replaced with parts having specification equal to those
originally installed.
2
F-20
SPECIFICATIONS
Rated Output Power: |
20W |
Speaker: |
20cm x 1 |
Controls: |
VOLUME, GAIN, MASTER VOL., TREBLE, MIDDLE, BASS, CH SELECT switch (A/B) |
Input/Output Terminals: |
INPUT, AUX IN, PHONES |
Output Impedance: |
100Ω (PHONES) |
Power Consumption: |
30W/100V (J) |
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25W/120V (UL,CSA) |
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25W/230V (E,BS) |
Power Requirements: |
U.S. and Canadian models: 120V, 60Hz |
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General model: 230V, 50Hz |
Dimensions (W x H x D): |
357 x 330 x 197mm (14.1" x 13" x 7.8") |
Weight: |
6.5kg (14 lbs 5 oz) |
PANEL LAYOUT
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INPUT
CH SELECT A/B (Channel Select Switch A/B)
AChannel
VOLUME
*No sound is produced when the VOLUME knob is set to "0".
BChannel
GAIN
MASTER VOL.
*No sound is produced when the MASTER VOL. knob is set to "0".
Tone Controls
TREBLE
MIDDLE
BASS
AUX IN
*Use the volume control on the audio device to control its volume level.
PHONES
* The speaker produces no sound when a pair of headphones is connected to this jack.
POWER
3
F-20
CIRCUIT BOARD LAYOUT
Top View |
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Side View |
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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
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CH. SELECT SW |
CH. B |
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CH. A |
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OP AMP |
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CLEAN |
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DRIVE |
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+B |
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INPUT |
+12V |
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SW2 |
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3 |
IC1 1 |
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OP AMP |
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IC1. IC2 |
OP AMP |
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VOLUME |
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+12V |
PASSIVE TYPE |
+12V |
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JK1 |
-12V |
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5 IC1 7 |
5 IC2 7 |
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VR1 |
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TONE CONTROL |
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-12V |
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-12V |
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OP AMP |
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INDICATOR |
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GAIN |
+12V |
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3 IC2 |
1 |
CH. A |
CH. B |
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VR2 |
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MASTER |
CLEAN |
DRIVE |
VR4 |
VR5 |
VR6 |
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-12V |
VR3 |
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TREBLE |
MIDDLE |
BASS |
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POWER SWITCH |
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FUSE |
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T1 |
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FZ1 |
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SW1 |
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T2 |
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2P |
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CN2 4P |
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CN33P |
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CN1 |
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POWER SUPPLY CIRCUIT |
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U, C, S, BS |
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T1 |
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G |
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T2 |
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POWER TRANSFORMER
V695450
AUX IN
JK3
MAIN 2/2
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+B |
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5P |
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5P |
1 |
IC3 |
4 |
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POWER |
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CN4 |
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CN5 |
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-B |
AMP |
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T3
T4
+B
+12V -12V -B
JK2
4Ω Speaker
PHONES
4
F-20
DISASSEMBLY PROCEDURE
1.Pre-Main Unit (Time required: about 1 min)
1-1 Remove the speaker wires.
1-2 Remove the four (4) screws marked [30]. The pre-main unit can then be removed by sliding it backward. (Fig.1)
2.Speaker (Time required: about 1 min)
2-1 Remove the four (4) screws marked [A]. The back board can then be removed. (Fig.1) 2-2 Remove the four (4) screws marked [B]. The speaker can then be removed. (Fig.1)
3. MAIN 1/2 Circuit Board (Time required: about 3 min)
3-1 Remove the pre-main unit. (See procedure 1)
3-2 Remove the six (6) knobs marked [P100] and the six (6) hexagonal nuts marked [C]. (Fig.5) 3-3 Remove the hexagonal nuts marked [A120] and the hexagonal nuts marked [A140]. (Fig.5)
3-4 Push the hooks of the spacer support (at the arrow symbol area of illustration) with a needle-nose plier to unlock. The Main 1/2 circuit board can then be removed. (Fig.2)
[30] x 4 |
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[B] |
Pre-Main Unit |
Pre-Main Unit |
Speaker |
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[A] |
Back Board |
[30]: Truss Head Screw 4.0X25 MFZN2BL (VN347600) |
[A]: Bind Head Tapping Screw 4.0X25 FCRM3-BL (EI340256) |
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[B]: Bind Head Screw 4.0X20 ZMC2BL (VB403600) |
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(Fig. 1)
Needle Nose Plier
[P40] |
MAIN1/2 Circuit Board |
(Fig. 2)
5
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