Dokorder 7700 User manual

DOKORDER
rnoder 77OO SERVICE MANUAL
sM, 1004-00
1977.3
sEcroN 1
TECHNICAL DESCRIPTION AND ADJUSTMENT
PROCEDURES
D
bokorder, lnc.
5430 ROSECRANS AVENUE, I-{WNDALE, CALIF. 90260 U.S.A.
r-rE\] Kr <)\JK-YO CO., r--trE).
26.1 1, 3-CHON4E, NISHI-ROKUGO, OTA-KU, TOKYO, JAPAN

TABLE OF CONTENTS
1. GENERAL DESCRIPTION 1
1 1 Amplifier Circuitry g
1-2 Tape Transport Mechanism
1-3 Power Supply Circuitry
2. SERVICE DATA 2
21 Mechanical
2-2 Electrical
3. PARTS LOCATION . 3-4
3-1 Outer Parts
3-2 lnner Parts
4. REMOVAL OF OUTER PARTS 5 r
4-1 Front Panel
4-2 Amp Panel
4-3 Top and Bottom Boards ../
5. ADJUSTMENT -MECHANTCAL- ... . 6-'11
5-1 Auto Shut-off Switch
5-2 Pinch Roller Drive Mechanism
5-3 Reel Motor Torques
5-4 Brake Mechanism
5-5 Tape Speed
5-6 Wow/Flutter g
6. ADJUSTMENT -ELECTRTCAL- .12-20
6-1 Adjustable Parts Location
6-2 Adjustment Procedures
7. MAINTENANCE . 21
7 -1 Cleaning
7-2 Lubrication
7 3 Demagnetizing y)
B. TECHNICAL DESCRIPTION ....22-31
8-1 Solenoid Drive Circuit
8-2 Capstan Drive Circuit
9. SCHEMATIC DIAG RAM
Note
This Service Manual consists of three sections:
Section 1: Descriptions of circuitry, operating procedures, and methods of adjustments
and maintenance, plus technical data.
Section 2: Exploded views, and parts list.
Section 3: Patterns, schematics and parts lists for printed Circuit boards. v

v
v
v
v
1. GENERAL DESCRIPTION
The Dokorder Model 7700 is a -track,2-channel,2-speed tape deck equipped with 3-motor, 3-heacl and sole-
noid operation facility. Designed for high dependability and electrical performance. Their features:
1.1 AMPLIFIER CIRCUITRY
1. The convenience features of the 7700's amplifier circuit such as the Monitor Switch. Mic AMp Circuit, Head-
phone AMP Circuit and Level Meter AMP Circuit built in.
2. 4-separate controls permit subtle input/output level adjustments.
3' 2-stepped Equalizer Switch is equipped to use for the several type of tapes. The relation between the tapes and
the position of the switch is illustrated below.
1-2 TAPE TRANSPORT MECHANISM
1. The convenience features of the 7700's tape transport such as the all-electronic operation buttons, pause con-
trol, tape travel counter are positive, and the mechanisms themselves are rugged and dependable.
2. fhe tape transport offers an Auto Stop convenience, and when the tape reaches its end in any mode (fast for-
ward, rewind, play or record). a solenoid releases the locked operating control (s) to place the deck in the stop
mode.
3. High dependability is proven by using newly improved electronic solenoid control system that reduces the
powerconsumption and heat up in the solenoid and its control transistors.
4. Especially high speecl-accuracy and surprising wow/fluttel characteristics are realized by using most advanced
PLL (Phase-Locked Loop) Servo System in capstan motor drive.
5. Newly designed high-torque outer-rotor eddy-current motor is used for reel drive.
1-3 POWER SUPPLY CIRCUITRY
1. The primary winding of the power transformer is provided two taps 100 V and 54 V. The former is used for
the reel motor drive in the fast winding mode. while the latter is used for the reel motor drive in the rec/play
mode.
2. On the secondary side, the transformer also offers two windinqs for 5.6 V and 14 V x 2. The former is used for
illuminating the pilot lamps, while the latter is rectified and then used to power the amplifiers, solenoid, PLL
circuit and capstan motor.
Equalizer Switch Type of Tape
Normal (button out) Scotch #212 or equivalents
Special (button in) Maxell #UD-35 or equivalents
v

2. SERVICE DATA
2-1 MECHANICAL
Record/Playback System 4 track 2 channel stereophonic
Tape Width Standard 1/4 inch tape
Reel Size 7-inch or smaller
Motor Three (one 2 speed PLL DC servomotor for capstan, two 6 pole induction
outer-rotor type for reels)
Head Three (1 erase, 1 rbcord, 1 playback)
Tape Speed !1 .5o/oat 19 cm/sec (7-1 l2ipsl ,!1 .5%at 9.5 cm/sec (3 3/4 ips)
Wow and Flutter Playback (RMS)
0.13o/oat 19 cm/sec (7 112ipsl ,0.20% at 9.5 cm/sec (3-3/4 ips)
Fast Winding Time 100 sec for 7-inch reel (1800-foot tape, 60 Hz)
Motor Torque Hold-back tention (playback) 85 gr 110 gr (255 t30 g.cm)
Take-up torque (playback) 150 gr (450 g.cm)
FFlREW hold-back tention 30 gr ( 90 g.cm)
Brake Torque 600 - 800 gr (1.8 - 2.4 kg.cm)
weight 35 lbs
Dimension 17-314" (H) X 16-718" (W) X 6 3/4" (D)
2-2 ELECTRICAL
al
v
Y/
V'
Equalization
Bias Frequency
Frequency Response
(Playback )
Frequency Response
(Overa ll )
One-channel Recording
Signal to Noise Ratio
Crosstalk
Channel Separation
Bias Leakage
Erase Ef{iciency
Distortion (Overall)
Meter Calibration
lnput Mic
L ine
DIN
Output Line
DIN
Circuit Complement
Power Consumption
Power Requirement
Headphone 2mW 8Q
NAB
130 KHz +1 KHz
.19 cm/sec (7 l12ipsl
50 - 100 Hz l! oa, 1o1 Hz - 1 5 KHz 13 dB
o 9.5 cm/sec (3 3/4 ips)
50 Hz - 7.5 KHz 13 dB
o 1 9 cm/sec (1-1 12 ips)
Normal 30 Hz - 20 KHz t3 dB (30 - 100 Hz, 15 - 20 KHz t5 dB)
Special 30 Hz - 20 KHz 13 dB (50 - 100 Hz, 15 - 20 KHz t5 dB)
o 9.5 cm/sec (3-3/4 ips)
Normal 35 Hz- 12KHz t3dB (35 -'1 00 Hz, 1.5- 12 KHz15 dB)
Special 35 Hz - 12 KHz 13 dB (35 - 100 Hz, 7.5 - 12 KHz 15 dB)
TOOHzll dB, 15 KHz+5dB at 19 cm/sec (7'1 /2ipsl
500 Hz 11 dB, 7.5 KHz +5 dB at 9.5 cm/sec (3-314 ips)
Better than 50 dB (Playback) at 0 dB output level
Better than 46 dB (Overall) at 0 dB output level
Better than 50 dB at 1 KHz
Better than 40 dB at 1 KHz
Less than -25 dB
Better than 65 dB at 1 KHz
Less than 3% at 1 KHz 0 dB output level
0 dB at IOOHz 0 dB output level (P.8. VR-Max)
-58 dB 10 KO (load imPedance)
-20 dB 220 K9
30 mV 80 KQ
OdB 47KQ
260 mV 47 KS)
34 transistors, 29 diodes, 5 lC,2 FET ,2 LED, 1 PUT
75W
U.S.A. type 117 V (60 Hz)
Universal type 100 V,117V,125V,20OV,220V,24O V (50/60 Hz)
Specs are subject to change withor-rt notice.
v

3. PARTS LOCATION
3-1 OUTER PARTS
v
v
v
Front View
20 Push Button, Metal, EO, Speed, Monitor, Pause SW
21 Push Button, Red, Rec. SW (556-0009-00)
22 Operate Button, Rec. (556-0038-80)
23 Ope. Button, FF & REW (556-0037-80)
24 Ope. Button, Stop (556-0035-80)
25 Ope. Button, Plav (556-0036-80)
26 Level Meter (141-1004-00)
Back View
1 Panel Ass'y, Deck (880-0017-00)
2 Panel Ass'y, Amp (880-0018-00)
3 Side Board {551-0018-02)
4 Top Board (551-0013-90)
5 Bottorn Board (551-00'10-00)
6 Foot Ass'y (880-0019-00)
7 Head Cover {880-0016-00)
8 Counter (143-31 02-00)
9 Turn Table Ass'y (810-001 1-00)
1O Dressing Washer, Pinch Roller (555-0050-02)
11 Pinch Roller (523-0029-00)
12 Tape Guide(L), Tension Arm (558-0020-00)
13 Tape Guide(R), Tension Arm (558-0021-00)
14 Switch, Push, Power (131-1018-80) or (131-1019-80)
15 Switch. Push, EO. Select (131-1014-00)
16 Switch, Push,2-station Speed & Monitor (131-10i5-00)
17 Switch, Push, 2-station, Rec. (131-1017-00)
18 Switch, Push, Pause {131-1016-00)
19 Push Button, Metal, Power SW (556-0030-02)
(556-0013-83)
fiililfi1
tiilltill
27 Control Knob, Metal (556-0001-00)
28 Jack. Mic (135-5001-00)
29 Jack, Headphone {135-5002-00)
30 Cup Washer (532-0021-00)
60 Back Board (551-0019-03) or (551-0020-00)
61 AC Cord with Plug (162-1001-00)
62 Holder, F use 1135-7001-00)
Fuse, 1.5 A (138-1003-00)
63 Jack, 4-Pin (1 35-5008-00)
64 Terminal, GND (135-1001-00)
65 Socket, DIN (136-6003-00)
ar

3.2 INNER PARTS a
Front View
31 Solenoid, Brake, DC-24V 48 ohm (1 1 6-2002-00)
32 Linkage, Brake (525-0025-00)
33 Stopper, Brake Linkage (528-0008-00)
34 Linkage, Brake Solenoid (525-0027-00)
35 Bracket, Brake (533-0082-00)
36 Guide, Brake Linkage (528-0009-00)
37 Spring, Brake (541-0007-05)
38 Solenoid, Pinch Roller Pressure, DC-24V 15 ohm
(1 1 6-2003-00)
39 Spring, Pressure (541-0010-01 )
40 Arm, Pinch Roller Drive (525-0029-00)
41 Arm, Pinch Roller (525-0032-00)
42 Shaft, Pinch Roller (521-0025-05)
43 Arm, Auto Shut-Off (525-OO24-O4\
44 Switch, Micro, Auto Shut-Of f (131-3001-00)
45 Bearing, Capstan 1522-OO1O-O2)
46 Dressing Plate, Tape Lifter (521-0029-00)
4-l Head Base Ass'y (830-001 1-00)
48 PC Board Ass'y (PCM-365A), Head Connect (831-0004-00)
49 Tension Arm Ass'y (Left) 1840-0016-00)
50 Tension Arm Ass'y (Right) (840-0018-00)
51 Pulley, Motor, No.3 (523-0031-04)
52 Belt, Capstan Drive 1524-OoO7-O2l
53 Belt, Counter Drive (524-0006-00)
54 PC Board Ass'y (PCM-3978), Rec. & Pause (821'0020 00)
55 PC Board Ass'y (PCM-3954), LED (821-0019-00)
56 Switch Ass'y, Operate (820-0016-00)
57 Chassis(A), Amp. (512-001 1-83)
66 Power Transformer (1 1 1-1021-00)
67 Resistor, Wirewound, 1200 ohm 20W \3O2-122O-8O)
Resistor, Wirewound, 600 ohm 15 W {302-6018-90)
68 Resistor, Wirewound, 200 ohm 10 W {302-2018-90)
Resistor, Wirewound, 150 ohm 10 W (302-1518-90)
69 Motor, Reel (113-1002-00)
70 Motor, Capstan (114-5001-00)
71 PC Board Ass'y (PCM-4118), Capstan Motor (861-0003-00)
72 PC Board Ass'y (PCM-361C), Capacitor, Reel Motor
(161-1034-00 )
73 PC Board Ass'y (PCM-417C), Control (851-0008-00)
74 PC Board Ass'y (PCM-4138), Bias OSC (851-0009-00)
75 Arm, Flywheel Support (533-0020-02)
76 Flywheel {523-0030-01 )
77 PC Board Ass'y (PCM416E), Operate SW (821-0021-O0)
78 PC Board Ass'y (PCM4464), Amp. 1871-0012-00)
79 Chassis(A), Power Supply (533-0048'01)
Chassis (B), Power Supply (533-0049-00)
80 Chassis(B), Amp. (512-00'l 2-00)
2-
u
?
**- '**
2,

4. REMO\/AL OF OUTER PARTS
'Y
U
v
4.1 FRONT P
1. Referring to Fig. 4-1. withdraw head cover O
and remove head cover posts @ by turning them
counterclockwise with pliers or box driver.
2. Holding pinch roller @ stitl, turn counterclock-
wise screw @ securing pinch roller dressing
washer @ and withdraw the screw together with
the dressing washer. Then extract nylon washer
@ anO the pinch roller from the pinch roller
s h aft.
NOTE: When extracting the pinch roller, take
care not to lose the nYlon washer.
3. Remove four screws @ anA @ securing the
front panel by turning them counterclockwise;
then remove the panel itself by moving it as the
arrow in the illustration shows.
NOTE: When mounting the front panel, reverse
the steps described above. Take note that
cup washer @ should be fitted on the
two screws securing the bottom part of
the front panel. Also, note that conduc-
tive rubber washer @ shoutO be f itted
on the screw securing the right side of the front panel. This is for grounding the front panel.
v
4-2 AMP PANEL
1. Withdraw control knobs-RECORD LEVEL CONTROLS and PLAYBACK LEVEL CONTROLS.
2. Remove the two screws (BS-3 X 6) above and (BS-3 X 18) below the level meters by turning them counter-
clockwise. Then, remove the four screws (BS-4 X 15) that secure the amp panel.
NOTE: Take care not to lose the nylon washer when'removing the two screws above and below the level
meters.
3. When mounting the amp panel, reverse the steps described above'
NOTE: Fit and tighten the screws only after checking to see that the record indicator LEDs are correctly
fitted in the holes on the amp panel and that the level meters are also fitted correctly in the amp
panel holes. Take note that the conductive rubber washer should be fitted on the screw that secures
the upper right side of the amp panel (see 4-1. 3 above)'
4.3 TOP AND BOTTOM BOARDS
1. Remove the six black-painted screws (RS-3 X 6) that secure the top board.
2. To remove the botrom board, remove the four screws {RS-3 X i4) securing the two FOOT ASS'YS by turning
them counterclockwise. Then remove the FOOT ASS'YS themselves'
3. With the FOOT ASS,YS dismounted, remove the screw (RS-3 X 8) securing the bottom board at its center by
turning it counterclockwise, then remove the bottom board itself'
4. When mounting the top and bottom boards, take care not to confuse the screws securing the top board with
those securing the bottom board; they are different in size and finish.
(e)
aI
F-a
Fig.4-1
v

3-2 INNER PARTS
*T*-
v
Front View
Back View
ffiir:t:rj':::.. : :- -:;.. :'. .:.:ii.::':::l:;.=?:@
31 Solenoid, Brake, DC-24V 48 ohm (1 1 6-2002-00)
32 Linkage, Brake (525-0025-00)
33 Stopper, Brake Linkage (528-0008-00)
34 Linkage, Brake Solenoid (525-0027-00)
35 Bracket, Brake (533-0082-00)
36 Guide, Brake Linkage (528-0009-00)
37 Spring, Brake (541-0007-05)
38 Solenoid, Pinch Roller Pressure, DC-24V 15 ohm
(1 1 6-2003-00)
39 Spring, Pressure (541-0010-01 )
40 Arm, Pinch Roller Drive (525-0029-00)
41 Arm, Pinch Roller (525-0032-00)
42 ShaIt, Pinch Roller (521-0025-05)
43 Arm, Auto Shut-Off 825-OO24-O4)
44 Switch, Micro, Auto Shut-Off (131-3001-00)
45 Bearing, Capstan \522-OO1O-O2)
46 Dressing Plate, Tape Lifter (521-0029-00)
4-l Head Base Ass'Y (830-001 1-00)
48 PC Board Ass'y (PCM-365A), Head Connect (831-0004-00)
49 Tension Arm Ass'v (Left) (840-0016-00)
50 Tension Arm Ass'y (Right) (840 0018'00)
51 Pulley, Motor, No.3 (523-0031-04)
52 Belt, Capstan Drive 1524-OOO7-O2)
53 Belt, Counter Drive {524-0006-00)
54 PC Board Ass'y (PCM-3978), Rec. & Pause (821-0020-00)
55 PC Board Ass'v {PCM-395,4), LED (821-00i9-00)
56 Switch Ass'y, Operate {820-0016-00)
57 Chassis(A). Amp. (512-0011-83)
66 Power Transformer (1 1 1-102 1-00)
67 Resistor. Wirewound, 1200 ohm 20 W \3O2-122O-8OI
Resistor, Wirewound, 600 ohm 15 W (302-6018-90)
68 Resistor, Wlrewound, 200 ohm 10 W (302-2018-90)
Resistor. Wirewound, 150 ohm 10 W (302-1518-90)
69 Motor, Reel {1 1 3-1 002-00)
70 Motor, CaPstan (1 14-5001'00)
71 PC Board Ass'y (PCM-4118), Capstan Motor (861-0003-00)
72 PC Board Ass'y (PCM-361C), Capacitor, Reel Motor
(161-1034-00)
73 PC Board Ass'y (PCM'417C), Control {851-0008-00)
74 PC Board Ass'v {PCM-4138), Bias OSC (851-0009-00)
75 Arm, Flywheel Support (533-0020-02)
76 Flywheel (523-0030-0 i )
77 PC Boarcl Ass'y (PCM-416E), Operate SW (821-0021-00)
78 PC Board Ass'v (PCM-446Ai, Amp {871-0012-00)
79 Chassis(A), Power Supplv (533-0048-01)
Chassis (B), Power Supplv (533-0049-00)
8o chassis (B), AmP. (512-0012-oo)
v
?.'-
u,
Q9(B) I
*-l
€re1I
u- v-

5. ADJUSTMENT -MEGHANICAL-
5.1 AUTO SHUT.OFF SWITCH
a. Specification
When the auto shut-off urrn @ is pushed upward,
the microswitch @ clicks lswitches on) at the
point of more than 8 mm (0.32 inch) outside of
the tape travel position and clicks again (switches
off) at the point of more than 14 mm (0.56 inch)
outside of the tape travel position.
b. Adjustment
Adjust the mounting position of the microswitch
@
c. Reference
Refer to Fig.5 1 or section 2 on page M-12.
d. Special Tools and/or lnstruments required
N one
e. Preparation
Remove the head cover and front panel.
f. Procedure
(1) Check the on/off position of the microswitch by gently moving the auto shut-off arm by hand.
(2) lf the on/off position does not meet the spec, adjust the position of the microswitch by loosening two
mount screws @.
g. Note
(1) Replace the dismounted parts and check again that the auto shut-off arm moves freely through the hole
in the front panel and does not come into contact with head cover.
(2) Load the tape and set the deck in play mode and check if the tape travels normally. Then take up the tape
completely by setting the deck in FF or REW mode, checking that the auto shut-off arm returns to shut
off the tape travel automatically at the tape end.
5.2 PINCH ROLLER DRIVE MECHANISM
2.1 STROKE ADJUSTN/IENT OF THE PINCH ROLLER PRESSURE SOLENOID
a. Specification
Stroke of plunger 4 - 4.5 mm (0.16 - 0.18 inch).
b. Adjustment
Adjust the stroke adjusting nut @.
c. Reference
Refer to Fig.5-2 or section 2 on page M-20.
d. Special Tools and/or lnstruments required
A open end wrench (4 mm).
e. Preparation
Remove the front panel (including pinch roller and
head cover).
Fix the auto shut-off arm ON by a piece of
sticking tape.
f. Procedure
(1) Push the play and stop buttons alternately several times, mark the position of the solenoid plunger @ as
it pulls and returns.
(2) Adjust the nut @ ro that the operating stroke of the plunger (indicated ur @ ) is from 4 to 4.5 mm
(0.16 - 0.18 inch).
g. Note
a
lvlount(auto shur-011 swirch2Tape Travet Posrtion
\^@r/
61 ;* (up"cu,a" =
qls
Dressing Plate z
?,
a.
@roct< lusting Nut
Pressure Spring
@Pressure Solenoid Pinch Roller Drive Arm
Fis.5-2
b
(i ) Loosen the lock nut @ first and then proceed with step f-(2).
(2) After the stroke has been adjusted. fix the nut @ with the lock nut @, tt.'.n paint-lock it.
?

(1) Read the pressure indicated on the spring
balance when the pinch roller loses contact with the capstan and the pinch roller stops revolving
(2) Adjust the pressing force of the pinch roller by turning the nut @ and @, if nec.ssaty.
rY g Note
(1) Use a precision spring balance with a scale of up to 4 kg graduated in steps of 50 g or less.
(2) Loosen lock nut first before attempting step f-(2).
(3) Fix the adjusting nut @ with the lock nut @ and then paint-lock it.
5-3 REEL MOTOR TOROUES
2-2 PINCH ROLLER PRESSURE
a. Specification
1 '5 ks tQ"l Pg
r.t b. Adlustment
Adjust the pressure adjusting nut @.
c. Reference
Refer to Fig. 5-3 or section 2 on page M-20.
d. Special Tools andlor lnstruments required
A open end wrench (4 mm) and spring balance
(4 kql'
e. Preparation
Remove the front panel (including pinch roller
and head cover).
Fix the auto shut-off arm ON by a piece of
stickinq tape.
f. Procedure
a. Speci{ication
y Hold-back Tension 85 gr 110 gr (255 +30 g. cm)
Take-up Torque 150 gr (450 g. cm)
b. Adjustment
Adjust the wirewound resistor R-2 (150 ohm) for
the hold-back tension.
c. Reference
Refer to Fig. 5 4, 5-5 or section 2 on page M-22.
d. Special Tools and/or lnstruments required
A spring balance (200 q) and 7-inch small-hub reel
ry (6 cm in diameter).
e. Preparation
Remove the back and top boards.
Fix the auto shut-off arm ON by a piece of
sticki ng taPe.
f. Procedure
f-i. Hold-back tension (Playback)
(1 ) Mount the 7-inch reel on the left turntable
with a piece of string attached to it, as shown
in Fig. 5-5 (A).
(2) Set the deck in play mode and pull the spring
balance gently in the direction indicated by
the arrow in F ig. 5 5 (A) and read the
indicated figures on the spring balance.
(3) Loosen lock screw @ securing the slide ring
O on the R-2 in Fig. 5-4 and adjust the
position of the slide ring so that the spring
U balance indicates 85 g 110 9 (255 g. cm 130).
f-2. Take-up torque (Playback)
Pinch Roller
Capstan Shaft
Capstan Bearing
Fig.5-3
\Pinch Roller Arm
@stioe ning
@Lock Screw---
lncrease{-- --->Decrease
Fig.5-4 "Moror chasis
/^-\-i
\ t)---< )
, \,fo oo\.,"
q\
4.^/
\\\//
tlo \ /
\\ \ / /
\ L-/ ,,',
F ig.5-5
(1) Mount the 7-inch reel on the right turntable with a piece of string attached to it. as shown in Fig. 5-5 (B).