Yamaha k 903

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STEREO DOUBLE CASSETTE DECK

KX-W421/W321/K-903

. ' SERVICE MANU

/ 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: 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 perform as specified. For these reasons, we advise all YAMAHA product
owners that any service required should be performed by an authorized YAMAHA
Retailer or the appointed service representative.

IMPORTANT: The presentation or snie of this manual to any individual or firm does not constitute
authorization, certification or recognition of any applicable technical capabilities,
or establish a principle-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 0! YAMAHA are continually striving to improve YAMAHA products.
Modifications are, therefore, inevitable and specifications are subject to change without notice or obligation
to retrofit. Should any discrepancy appear to exist, please Contact the distributors Service Division.

WARNING: 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).

IMPORTANT: Turn the unit OFF during disassembly and part replacement. Recheck all work before

you apply power to the unit.

I CONTENTS

TO SERVICE PERSONNEL DISPLAY DATA .................. . 19
FRONT PANELS .................. KX-W421 BLOCK DIAGRAM .. . 20
REAR PANELS ............................................................... 3 SCHEMATIC DIAGRAM ......................................... 21 ~23
KX-W421 SPECIFICATIONS.. KX-W321IK-903 SPECIFICATIONS .. . 24
KX-W421 INTERNAL VIEW.... KXvW321lK-903 INTERNAL VIEW... . 24
DISASSEMBLV PROCEDURES 5~6 KX-W321IK-903 ADJUSTMENTS .................. . 25~29
KX-W421 ADJUSTMENTS .. . 7~11 KX-W321/K-903 PRINTED CIRCUIT BOARD . 30~33
KX-W421 PRINTED CIRCUIT BOARD ..12~15 KX-W321/K-903 BLOCK DIAGRAM .............. 34
u-COM DATA .......................................................... 16~1B PARTS LIST ............................................................ 3551

YAMAHA CORPORATION
P.0.Box1.Hamamatquapm

2.8K-514 (a) g Printed in Japan 98.3

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KX-W421/W321lK-903

I TO SERVICE PERSONNEL .

KX-W321/K-903
1. Critical Components information.

Components having special characteristics are marked Aand
must be replaced with parts having specifications equal to
those originally installed.

AC LEAKAGE
2. Leakage Current Measurement (For 120V Model only). WALL EQUIPMENT TESTER on
When service has been completed, it is imperative that you OUTLET UNDER TEST ' EQUIVALENT
i . . . _
V verify that all exposed conductive surfaces are properly rnsu G) D-
: lated from supply circuits. I
0 Meter impedance should be equivalent to 1500 ohm shunted INSflLBIENG
by 0.15pF.

O Leakage Current must not exceed 0.5mA.
0 Be sure to test for leakage with the AC plug in both polarities.

Dolby noise reduction manufactured under license from
Dolby Laboratories Licensing Corporation.
"DOLBY" and the double-D symbol [II] are trademarks of
Dolby Laboratories Licensing Corporation.

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 WHATSOEVER!

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.