Teac A-650 Service Manual

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TEAC
Stereo Cassette Deck with Dolby System
GENERAL INTRODUCTION
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NOTE
When ordering replacement parts, please refer to the
PARTS LIST which is printed separately from this
manual.
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; TEAC CORPORATION [
51031740
If any of the adjustments or repairs seem too complicated
or are difficult for you to accomplish, please contact the
nearest TEAC Factory Service Department or write directly
to a TEAC office, the addresses of which are printed on the
back cover.
This Service Manual is designed to provide up-to-date
information to assist the skilled service technician to prop 
erly repair, adjust and maintain the TEAC A-650 Stereo
Cassette Tape Deck.
The A-650 is a high quality deck designed to be used as an
indispensable part of a superior home stereo system. It
contains a 2-motor transport utilizing a DC reel motor and
a Phase Locked Loop (PLL) servo motor, push button
control panel, Memory Counter with Play feature, Record
Mute feature, advanced Dolby NR circuitry, Peak indica 
tors, Limiter, 3-position BIAS and EQ selector Switches, as
well as many of the standard TEAC features.
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* Noise reduction circuit made under license from Dolby
Laboratories Inc. The word “ Dolby ” and the Double-D
symbol are trademarks of Dolby Laboratories Inc.

Teac A-650 Specifications

General

Type	Cassette Deck
Track System	4-track, 2-channel stereo
Motor	DC servo motor
Output	Line
Heads	1 x playback, 1 x record/playback, 1 x erase
Tape Type	CrO2, Metal
Wow and Flutter	0.04% (WRMS)
Total Harmonic Distortion	0.8%
Input	Line
Input Sensitivity/Impedance	0.25 mV (mic)
Output Level/Impedance	0.775 V

Summary

Test Equipment Required for TEAC A-650 Service

Test Equipment for TEAC A-650 Service

TEAC A-650 Specifications and Service Data

TEAC A-650 Technical Specifications

Outlines the technical specifications for the TEAC A-650 cassette deck, including tape system and speed.

Partial Disassembly Procedures for TEAC A-650

Case and Front Panel Removal

Tape Transport Chassis Removal

Component Removal Procedures for TEAC A-650

Head Removal and Replacement

Detailed steps for removing, replacing, and adjusting the record/playback and erase heads.

Pinch Roller Removal and Adjustment

Major Component Replacement for TEAC A-650

Capstan Motor Replacement

Capstan Drive Assembly and Belt Servicing

Mechanical Checks and Adjustments

Take-Up Torque Measurement and Adjustment

Method for measuring and adjusting the take-up torque using a spring scale.

Fast Forward and Rewind Torque Specifications

Mechanical Adjustments for TEAC A-650

Pinch Roller Pressure Adjustment

Procedure to measure and adjust the pinch roller pressure for optimal tape contact.

Brake Tension Adjustment

Tape Speed and Wow/Flutter Tests

Tape Speed Measurement and Adjustment

Steps to measure tape speed using a frequency counter and adjust it.

Wow and Flutter Testing Methods

Procedures for testing wow and flutter in both playback and record/playback modes.

Control Panel Functionality Checks

Pushbutton Control Operation Checks

Verifies the correct operation of all front panel buttons like REC, PLAY, FF, REW, STOP, PAUSE.

Auto-End Stop and Memory Functions

Auto-End Stop Facility Check

Memory Device Function Tests

Electrical Adjustment Locations

Adjustment Potentiometer Locations and Functions

Diagram showing potentiometer locations and a list of their functions for calibration.

Playback Performance Verification

DC Voltage Adjustments (+13V, +24V)

Record/Playback Head Azimuth Adjustment

Steps to align the record/playback head azimuth for optimal signal phase.

Playback Performance Verification (Continued)

Specified Output Level Setting Procedure

Adjusts the line output level to the specified standard for playback.

Playback Frequency Response Testing

Measures and adjusts the playback frequency response for different tape types.

Playback Performance Verification (Continued)

Playback Signal-to-Noise Ratio Measurement

Checks the signal-to-noise ratio during playback for various tape types.

Playback VU Meter Calibration

Monitor Performance Testing

Minimum Input Level Checks

Verifies the minimum signal levels required for line, microphone, and DIN inputs.

Specified Line Control Setting

Record VU Meter Calibration

LED Peak Level Indicator Calibration

Recording Performance Adjustments

Dolby NR Copy-Out-FM Switch Function Check

Bias Trap Adjustments

Recording Performance Adjustments (Continued)

Record Bias Setting for Various Tapes

Details the process of setting bias levels for CrO2, Fe-Cr, and Hi-Fi tapes.

Recording Performance Adjustments (Continued)

Record Level Setting Procedure

Adjusts the recording input level for different tape types to achieve optimal recording.

Distortion Checks for All Tape Types

Overall Response and Noise Measurements

Overall Frequency Response Testing

Overall Signal-to-Noise Ratio Measurement

Performance Measurement Details

Dolby NR Effect Measurement

Peak Limiter Efficiency Checks

Tape Efficiency Tests

Erase Efficiency Measurement

Audio Channel Performance

Channel Separation Measurement

Audio Track Performance

Adjacent Track Crosstalk Measurement

Circuit Schematics

TEAC A-650 Block Diagram Overview

Provides a schematic overview of the internal circuitry and signal flow.

Signal Flow Diagrams

Playback and Recording Level Diagrams

Illustrates signal levels at various points in the playback and recording sections.

Troubleshooting Guide for TEAC A-650

Tape Transport Section Troubleshooting

Addresses common problems and their probable causes and solutions for the tape transport mechanism.

Amplifier Section Troubleshooting

Covers common problems and solutions for the audio amplifier circuits.