Dokorder 7700, Service Manual

Page 1: ...ERVICE 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 ...

Page 2: ...tor 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 c...

Page 3: ...e 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 usi...

Page 4: ... 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 ...

Page 5: ...ssing 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 55...

Page 6: ...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 2...

Page 7: ...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 ...

Page 8: ...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...

Page 9: ...ape 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 Refere...

Page 10: ...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 tensio...

Page 11: ...gain and loosen the two lock_screws securing the bracket to that the space between rhe brake band and the brake drum will be from 1 to 1 5 mm 0 04 0 06 inch Moving the bracket in the directin of arrow will increases the space Keeping the tape deck in the stop mode push the brake linkage downward by hand check that the brake band contacts the inside of the brake band guide 5 uniformly and that the ...

Page 12: ... 5 on page 7 d Special Tools and or lnstruments required A spring balance 1 kg and 7 inch small hub reel 6 cm in diSmeter e Preparation Remove the f ront panel including pinch roller and head cover Fix the auto shut off arm ON by a piece of sticking tape Procedure 1 Mount the 7 inch reel on the left turntable with a piece of string to it as shown in Fig 5 5 A 2 Push the stop button hook a spring b...

Page 13: ...andwowarewithinspecifications 5 6 WOW FLUTTER L t L a Specification 19 cm sec 7 l12iPs r 0 13 RMS 9 5 cm sec 3 3 4 iPs 0 20 RMS b Adjustment Adiust the motor torque pinch pressure alignment of tape path c Reference RefertoS 1 5 2 5 3 5 4and5 5describedaboveformechanicaladiUstment d Special Tools and or lnstruments required TesttapeDTT s114 1gcm sec DTT 3114 9 5cm sec oritsequivalents wow flutterme...

Page 14: ...k for rubbing parts or marred surfaces 4 Measure the wow if it exceeds the specification measure and adjust the reel motor torque 5 ln most cases the measured wow flutter should meet the specification by the time you reach the 3rd or 4th step above lf not a faulty pinch roller capstan or belt may be the cause and replacement is called for Usually replacement of a motor should not be considered sho...

Page 15: ...e alreadyadjusted lfyouareusingatapeforttretlrsttime it softenadvisabletocheckitsresponsebefore hand to know how different it is in response from the previous tape NOTES L L L TheproceduresinthissectionapplytotheamplifiercircuitsoftheModelTT00 ln adjusting the amplifier i cuits following the instructions in this section the tapes belowlisted should be used 1 When adiusting the playback circuits lt...

Page 16: ... PARTS LOCATION ArvrP P c B PCM 4464 BrAS OSC P C B PCM 4138 REC PAUSE P C B PCM 3978 1gcm 7 112 ips IP7 TP8 oo oo o L 401 o BIAS OSC ADJ TP 4 O TP s O L601 o L 03 S L 602 S c 06 M c 604 ffi o Fis 6 1 BIAS TRIMMER 13 ...

Page 17: ...e as shown Fig 6 5 on page20 3 When the azimuth adjustment is completed paint lock the azimuth screw h Note Since head azimuth is already adjusted before the deck leaves our Dokorder factory normally azimuth adjust ment is unnecessary it is necessary only when heads are replaced 2 2 PLAYBACK a Specification 1 0 dB r0 5 dB of the line output iacks b Adjustment Adjust the semi fixed resistors VR 106...

Page 18: ...lay the test tape DTT 5102 and check the output level is within the range of 10 dB 3 dB 5 dB in reference to the level 700 Hz 10 dB 4 Change the tape speed switch to the 9 5 cm s position then play the test tape DTT 3110 and adjust the semi fixed resistors VR 104 and VR 204 on the AMP PC Board so that the line output levels may be 10 dB 11 0 dB in reference to the level 500 Hz 10 dB 5 When the ste...

Page 19: ... when the tape deck is placed horizontally or in a slanted position be sure to undertake the adjustment with the tape deck placed vertically 2 6 BIAS FREOUENCY Specif ication 130 KHz 11 KHz Adjustment Adjust the oscillator coil L 40 l 1139 Reference Refer to Fig 6 1 d Test tape special tools and instruments required Frequency counter e Test point Connect the frequency counter across the test point...

Page 20: ...ss than 30 dB b Adjustment Adjust the bias trap coils L 1O2 and L 2O2 c Reference Refer to Fig 6 1 d Test tape special tools and instruments required Blank tape and VTVM e Test point Connect the VTVM to the line output jacks f Mode of switch 1 Monitor SW TAPE Record SW ON 21 P B level controls MAX Record level controls MlN g Procedure 1 Aftertheaboveconnectioniscompleted loadtheblanktapeonthedecka...

Page 21: ...rew c Reference Refer to Fig 6 3 Fig 6 5 or section 2 on page M 20 d Test tape special tools and instruments required Blank tape Scotch 212 t oscilloscope signal generator and VTVM e Test point Connect the VTVM and oscilloscope to the line output jacks f Mode of switch 1 Tape speed SW 19 cm s Monitor SW TAPE Equalizer SW NORMAL Record SW ON 2 P B level controls MAX Record level controls MAX g Proc...

Page 22: ...utput level of the frequencies between 500 Hz and 10 KHz is in the range of 3 dB in reference to the level 500 Hz 10 KHz 10 dB t2 dB and also that the line output level of the frequencies between 500 Hz and 35 Hz is in the range of t3 dB in reference to the level 500 Hz 35 Hz 10 dB 13 dB v 2 12 OVERALL FREOUENCY RESPONSE 19cm a SPecification TOOHz0dB 10d8 21 KHz 2 d8 30 Hz13dB b Adjustment Adiust ...

Page 23: ...ed load the blank tape Scotch 212il on the deck and push the record and play buttons simultaneously to enter the record mode By sweeping the frequency from 7OO Hz to 20 KHz with the signal generator check that the line output level is flat across the specified frequencies Then set the frequency to 20 KHz 3 Set the left record switch OFF to record only in the right channel Then record only in the l...

Page 24: ...ne on the pulleys and flywheel where belts are in constant contact so clean pulley and flywheel carefully Dirt deteriorates the wow characteristic of the deck 7 2 LUBRICATION We suggest you lubricate parts only after running the deck for one hour or two for by then the rotating parts will have warmed up enough to facilitate lubrication a Motor Apply one or two drops of oil each to its motor bearin...

Page 25: ...r solenoid and brake solenoid Then the pinch roller solenoid and brake solenoid draw and pinch roller pressurizes the capstan and releasing the brake Within 150 m sec to 300 m sec the Time Delay switch is automatlcally turned to the Vr 15 V position so that the pinch roller sotenoid and brake solenoid are both set to operate at a reduced voltage This condition is then maintained throuqhout the PLA...

Page 26: ...drive circuits are omitted Based on Fig 8 3 the operation of the circuit in individual modes will be illustrated with figures and brief descriptions 1 STOP mode 4 Switching from STOP to REC mode Fig 8 3 on this page Fig 8 6 on page 25 2 Switching from STOPto PLAY mode 5 Turning PAUSE switch ON OFF in REC mode Fig 8 4 on page 24 Fig 8 7 on page 2b 3 Switching from STOP to FF or REW mode 6 Turning A...

Page 27: ...1 ir e t O 50i t Jrrr O 5 l olf f i p Tr th lhF N r r e hPs sn r de r t q Ze net d d t l i L i t a l i n p oen a s n r 3 tvatld at tr s me l orf 5i i r i se o oFF nu D l lrip Fig 8 4 REC SIGNAL MUTE a rJ I i STOP to FFlREW mode SOLENOID Fig 8 5 24 ...

Page 28: ... to REC mode Charglng cunsnl pases th o qh C 503a dcs04tolqqe O501 EIAS OSC POWER SUPPLY REC SIGNAL MUTE MUTING N raq 6FFl Fig 8 6 I I i I I REC to pause ON OFF mode BIAS OSC POWER SUPPLY REC SIGNAL MUTE 25 ...

Page 29: ...ure of DC motors however have introduced compact but high performance DC motors ln addition supported by the development of servo techniques to drive and control DC motors low cost compact and low power consumption motors have become available that combine the advantages of the DC motor and servo control circuit This combination ensures sufficiently stable motor speed s and prom i nent wow f I utt...

Page 30: ... 2 B Operation Principle of Circuit Blocks in PPL Control Section 1 PLL Control Circuit O Motor design The torque required of the capstan motor is determined by the load applied to the tape deck The motor s output torque and supply voltage are determined so that the motor torque required for the permitted over or under voltage condition 110 may be obtained in each operation mode when the FG output...

Page 31: ...he inertial moment with the motor rotating at a frequency slightly lower than the synchronization frequency ln order to avoid setting flip flop FFs when Nr 2 and accelerating the motor flip flop FFg is forced to reset by time constant T3 for the period from when the PLL control is started to when Nr Nv 1 is established Nr 2 Nvz 2 Acceteration f oo Synchronization Rise Characteristic of Fv from zer...

Page 32: ...hese prohrlems 1fl_ 680K 512H2 o oo39 0 0012 I c 1M 10K lrl PUT OSC Voltage conversion 1 2 frequencv d ivider Fis 8 12 ln the above figure the oscillating frequency is given by 1 i _ Josc a ln 1_ nl Substituting for constants a ffi o R1 R1 R2 stand off ratio 1 6 8X 10s X 5 1 X 10 e t t 544H2 t J osc Max fosc Min f r fif 1 474H2 Thusthel00kSrpotentiometercanvarytheosciltatingfrequencyintherangefrom...

Page 33: ...otive force to the base emitter of transistor 01 a feedback is provided to maintain the motor speed against load variations and power voltage fluctuations lf Bz increases the voltage drop across Oz will increase to keep the motor voltage constant while the pulse width will also be kept constant Figs 8 15 and 8 16 The motor is also driven to the rated speed against variations in the load torque so ...

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