Teac A 420 Service Manual
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Page 1
SEIWIBE
MANUAL
A- 420
Stereo Cassette Deck with Dolby System
The TEAC A-420 is a front loading cassette deck with
independent rotary transport controls. It incorporates an
advanced motor and drive system, built-in Dolby noise
reduction system, peak level indicators, MIC/LINE mixing
capability, L/MONO microphone monaural recording func-
tion, TIMER control and selectable (three position) bias
and EQ as well as many of the standard TEAC features.
GENERAL INTRODUCTION
Simplicity of operation are combined with electronic and
mechanical dependability to make the A-420 a deck that is
not only reliable, but beautiful as well.
NOTE: When ordering replacement parts, please refer to
the PARTS LIST which is printed separately from
this manual.
* 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 CORPORATION I
51031800
Page 2
TABLE OF CONTENTS
1. Test Equipment Required ................ 3
2. Specifications & Service Data .............. 4
3. Parts Location ........................ 6
4. Partial Disassembly of Main Parts ............ 7
4-1. Case/ Front Panel .............. 7
42. Cassette Holder ............... 7
43. Head ...................... 8
4-4. Pinch Roller ................. 8
4-5. Tape Transport Chassis .......... 9
46 Motor ...................... 9
4-7. Capstan Drive Assy/Drive Belt . . . . . 10
4-8. Reel Tables .................. 10
4-9. Play Idler Assy ............... 11
4-10. Fast Wind Idler Assy ........... ll
5. Mechanical Checks and Adjustments ......... 12
5-1. Take-up Torque ............... 12
5-2. Fast Forward & Rewind Torque . . . . 12
5-3. Pinch Roller Pressure ............ 12
5-4. Tape Speed/Wow and Flutter ...... 13
5-4-1. Tape Speed .................. 13
5-4-2. Wow and Flutter .............. 13
5-5. Solenoid Position Adjustment ...... 14
56. Muting Switch Position Adjustment . . 14
6. Electrical Checks and Adjustment ........... 15
6-1. Monitor Performance ........... 16
6-1-1. Specified LINE Control Setting ..... 16
6-1-2. Minimum Input Level Checks ...... 16
6-1 -3. VU Meter Calibration ........... 16
6-1-4.
LED Peak Level Indicator Calibration . 17
6-2. Playback Performance ........... 17
6-2-1. Record/Playback Head Azimuth
Adjustments ................. 17
6-2-2. Specified Output Level Setting ..... 18
6-2-3. VU Meter Indication Checks ....... 18
6-2-4. Frequency Response Playback- ..... 18
6-2-5. Signal to Noise Ratio -Playback~ . . . . 19
6-2-6. Headphone Output Level Checks . . . . 19
63. Re cording Performance .......... 20
6-3-1. Bias Trap Adjustments ........... 20
6-3-2. Record Bias Setting ............. 20
6-3-3. Record Level Setting ............ 21
6-3-4. Distortion Checks .............. 22
6-3-5. Frequency Response -Overall- ...... 22
6-3-6. Signal to Noise Ratio -Overall- ...... 23
6-3-7. Erase Efficiency ............... 24
6-3-8. Channel Separation ............. 25
6-3-9. Dolby NR Effect Measurement ..... 25
6-3-10. Adjacent Track Crosstalk
Measurement ................. 26
6-4. Adjustment Location ........... 27
7. Block Diagram ........................ 28
8. Level Diagram ........................ 29
9. Trouble Shooting ...................... 30
TEAC Test Tape ............... 4
Lubrication .................. 14
Voltage and Frequency Setting ..... 15