Akai AT 2650 Service Manual

Page 2

SECHONI

SERVICE MANUAL

TABLE OF CONTENTS

I. TECHNICAL DATA ...................................................... 2
1. MODEL AT-2650 ................................................... 2
2-� MODEL AM»265O .................................................. 3
II. DISMANTLING OF UNIT ................................................... 4
1, MODEL AT72650 ................................................... 4
2. MODEL AM-2650 S
III CONTROLS ..................... 6
1. MODEL AT-2650 ..................................................... 6
2, MODEL AM-2650 .................................................... 7
IV, PRINCIPAL PARTS LOCATION .............................................. 8
11 MODEL AT-26SO ..................................................... 8
2. MODEL AM-2650 .................................................... 9
V. OPERATING PRINCIPLES OF QUADRATURE DETECTION SYSTEM .................... 10

VI. OPERATING PRINCIPLES OF PLL CIRCUIT EMPLOYED IN
STEREO DEMODULATION CIRCUIT ........................................ 12

1. PLL CIRCUIT OPERATION ............................................. 1-�

I, STEREO DEMODULATION CIRCUIT ............................ 13
VII, OPERATING PRINCIPLES OF FM NOISE CANCELLER CIRCUIT ....................... 15
1. BASIC CIRCUIT FOR PULSE NOISE SUPPRESSION .............................. 15
2. OPERATION PRINCIPLE WITH STEREO SIGNALS ............................... 15
3. ADJUSTMENT METHOD FOR THE PILOT SIGNAL GENERATING CIRCUIT ............. 16
VIII LEVEL DIAGRAM .......................................... I . 17
IX. TUNER ADJUSTMENT (AT-2650) ............................................. 18
I, FM TUNER SECTION ADJUSTMENT ........................................ 19
21 AM TUNER SECTION ADJUSTMENT ....................................... 20
X. AMPLIFIER ADJUSTMENT (AM-2650) ......................................... 21
1. IDLING CURRENT ADJUSTMENT .......................................... 21
2. LEVEL METER INDICATION ADJUSTMENT ................................... 22
XII TUNING CORD THREADING ................................................ 23
XII. CLASSIFICATION OF VARIOUS P.C BOARDS .................................. 24
1, PC BOARD TITLE AND IDENTIFICATION NUMBER ............................. 25
21 MODEL AT-2650 COMPOSITION OF VARIOUS P,C BOARDS ....................... 28
3, MODEL AM<2650 COMPOSITION OF VARIOUS PIC BOARDS ........................ 52

SC HEMATIC DIAGRAM

For basic adjustments, measuring methods, and operating principles, Iefer to GENERAL TECHNICAL
MANUAL

Page 20

1,FM TUNER SECTION ADJUSTMENT (Refer to Figs. 23, 24)

fl

Step Adjustment ltem Adjustment Point Result Remarks
M 'mu SELECTOR to PM MONO. FM
1 Front End 1F Coil 23;; em MUTE and NOISE CANCEL to
IF Coil (Front End) 3 OFF, Tune only noise without
Level . ,
interference of broadcasting.
. Centered
2 Tucnmg Meter T5 (WHT) Tuning Meter Same as above.
entering (Tuner P.C Board) , _
Indication
Distortion T6 (BLU) Less-than-�0.1% 98 MHz, 60 dB (mono) input,
3 Factor (Tuner P C Board) Distortion Less than 0.1% on both channels
' Factor See NOTE 1.
Confirmation If Tuning Meter Indication is not
of Tuning .
4 centered re-adjust Step 2 and
Meter 3 above
Indication '
High Range M x' mm 108 MHz, 60 dB (mono) input.
5 Scale TCo (Front End) 3 1!-� m TUNING INDICATOR to 108
Indication -� 9 MHz. Error: Within :250 kHz.
Effigxnfigf; M x'mum 88 MHz, 60 dB (mono) input.
6 s W D O -�1 m TUNING INDICATOR to as
.° . -� P MI-Iz. Error: thIn :250 kHz.
Indication
04
High Range TCA, TCRI, TCRZ, TCR3 Les? -�1-�-�? 3/-� 108 MHz, Less than 4 dB(mono)
7 Sensitivity (Front End) Distortion input
Factor -�
8 Low Range LRI, LR2, LR3 -�SitthftIE? 98 MHz, Less than 3 dB(mono)
Sensitivity (Front End) 1 O 1 input. See NOTE 2.
l Factor
Confirmation Less than 3% 98 MHZ, Less than 4 dB(inonc)
9 of Mid Range Distortion ,
. . . input. See NOTE 2.
SenSItiVIty Factor
PLL Free FM SELECTOR to FM AUTO.
. VR6 5 kB FM MUTE to ON. Connect
10 Running 1900 kHz .
Fre uenc (Tuner BC Board) frequency counter to Test Pom;
q V See NOTE 3.
Confirmation 98 MHZ. 60 dB (stereo) inpur.
of Stereo , . . .
11 , Unlet stereo Indicator indicans
Indicator 0 ter 0 tion
Lighting n s e separa .
Stereo VRl 20 kB More than FM MUTE to OFF. 98 MHz,
12 Separation (Tuner P C Board) 45 dB 60 dB (stereo), Lch input
(LeftnRight) ' Minimum output of R ch.
13 562:3)-� VRl 20 kB More than 98 MHz, 60 dB (stereo), Rm
(Right-deft) (Tuner RC Board) 45 dB Input Minimum output of L Ch
-� sr I '
. gna Meter VR4 50 kB Indicator .
14 l Sensitivity (Tuner P,C Board) at -�4.5-� 98 MHZ-� 100 dB (mono) input (-1
Curr H
NOTES: 1. When the distortion factor is not less than 0.1% in Step 3 adjust by turning the Front End IF C Oil

core but not more than 1/2 turn.
2. In the event that distortion factor in Step 9 is not less than 3%, re~adjust step 7 & 8 obtan 3%
distortion factor.
3. PLL IC free running frequency must be an exact 1900 kHz.

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