Text preview for : ReVox_A77_serv_man complete.pdf part of Studer ReVox A77 ReVox A77 reel tape recording machine.
Complete service manual incl amendments, all descriptions, circuit diagrams
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1. CONTENTS
2.
GENERAL 2.1. Front Panel Rear Panel
Page 4
5
3.
DISMANTLING 3.1. Removal of Housing 3.2. Removal of Cover Panel 3.3. Removal of Front Panel 3.4. Removal of Power Switch 3.5. Removal of Brake Unit 3.6. Removal of Reel Motors 3.7. Removal of Capstan Motor 3.8. Removal of Control Board 3.9. Removal of Power Transformer 3.1 0. Removal of Amplifier Cards 3.1 1. Removal of Potentiometer 3.12. Removal of Switch Board 3.13. Removal of Frame ( Removal of Rotary Switches)
4.
MECHANICS 4.1. Headblock 4.1.1. Tape Guides 4.1.2. Head Mounting 4.2. Tape Tension 4.3. Brakes ( Stop 4.3.1. Brake Torque Measurement 4.3.2. Brake Adjustment 4.4. Pressure Roller 4.4.1. Pressure Measurement 4.4.2. Pressure Solenoid Readjustment 4.4.3. Exchange of Pressure Roller 4.4.4. Pressure Lever Readjustment 4.5. Capstan Motor 4.5.1. Removal of Capstan Axis, Ball Bearings Exchange of Reel Motor Bearings 4.6. 4.7. Lubrication 4.8. End-of-Tape Switch ELECTRONICS Switch Board and VU-Meter Board 5.1. 5.2. Input Amplifier 5.3. Record Amplifier 5.4. Oscillator 5.5. Record Relay 5.6. Playback Amplifier Power Amplifier ( Loudspeaker Amplifier) 5.7. 5.8. Power Supply 5.9. Drive Control 5.9.1. Photoelectric End-of-Tape Switch 5.1 0. Speed Regulation, Capstan Motor
5.
6.
ELECTRICAL ADJUSTMENTS AND MEASUREMENTS 6.1. Demagnetizing 6.2. Tape Speed 6.2.1. Pick-up Head - Adjustment 6.2.2. Tacho Adjustment 6.2.3. Tacho Adjustment with Cathode-Ray Oscilloscope
6.3.
6.4.
6.5.
6.6.
6.7. 6.8.
Playback Adjustment 6.3.1. Azimuth Adjustment, Playback Head, Coarse (Max Level ) 6.3.2. Azimuth Adjustment, Playback Head, Fine ( Phase Method) 6.3.3. Playback Level from Test Tape 6.3.4. Frequency Characteristic, Playback ( from Test Tape ) Oscillator and RF-Adjustment 6.4.1. RF-Voltages and Frequency Checking 6.4.2. Dummy Load 6.4.3. RF-Traps, Record 6.4.4. RF-Traps, Playback Record - Adjustments 6.5.1. Azimuth Adjustment, Record Head, Coarse 6.5.2. RF-Bias 6.5.3. Azimuth Adjustment, Record Head, Fine 6.5.4. Record Level 6.5.5. Record Equalization 6.5.6. Frequency Characteristic via Tape Distortion Factor Measurement 6.6.1. Distortion Factor (via Tape ), VU-Meter Calibration 6.6.2. Noise Voltage ( and External Voltage ) via Tape 6.6.3. Noise Voltage, External Voltage " Before Tape" ( Check) 6.6.4. Erase Attenuation 6.6.5. Crosstalk, Mono 6.6.6. Crosstalk, Stereo Output Voltage Check Wow and Flutter
26 27 27 27 27 28 28 28 28 29 29 29 29 30 30 30 30 30 30 31 31 32 32 32 33 33
7.
ACCESSORIES 7.1. Remote Control 7.2. Timing Switch Operation MOD1FlCATlONS 8.1. Rewind 8.2. Switch Noise 8.3. RFI 8.4. Transfer Play Sensitivity 8.5. Replacement of Capstan Motor 8.6. Capstan Motor with Sleeve Bearings 8.6.1. Removal of Capstan Shaft and low-friction Thrust Washer TROUBLE SHOOTING 9.1. Faults in the Drive 9.2. Faults in the Circuitry DIAGRAMS Tape Drive VU-Meter Board Switch Board Input Amplifier Record Amplifier Oscillator Record Relay Playback Amplifier Loudspeaker Amplifier Speed Control REPLACEMENT PARTS LIST SPECIAL VERSION 12.1. Revox A77 - DOLBY Diag. 1 Diag. 2 Diag. 3 Diag. 3 Diag. 4 Diag. 5 Diag. 6 a Diag. 7 Diag. 8 Diag. 9 Diag. 10
8.
9.
10.
11. 12.
2. GENERAL
The Stereo-Recorder can be obtained as CHASSIS, WALNUT CABINET, and CARRYING CASE models. Here are the applicable codes ( order numbers
With 2 Output Ampl. Wood Cabinet Wood Cabinet Carrying Case Chassis Chassis
With 2x2 Loudspeakers
Codes 2-Track 4-Track 1102 1122 1222 1302 1322 1104 1124 1224 1304 1324
X X
X
X
Outline and Installation Dimensions, see : S 1 Following codes apply to accessories only :
Output Amplifier ( per Channel ) Walnut Cabinet Carrying case, incl. Cover and 2x2 Loudspeakers
1900 1950 1960
The basic configuration i s identical for all models. A pressure cast aluminum alloy chassis supports the 3-motor drive, one is the electronically regulated capstan motor. All amplifiers are plug-in modules.
An exchange service is organized for the circuit cards. Faulty cards will be exchanged at minimum charge by factory representatives in the respective country. The same applies to etched circuit boards with connectors ( control board, regulator, motor control, switch board ). This permits a very efficient service, limiting,in most cases, repair work t o finding the faulty module.
2.1.
Front Panel, Rear Panel
( Numbering corresponds t o REVOX
manual )
A
Push buttons
<< >>
PLAY STOP REC
Fast rewlnd Fast forward Playback Stops all operating functions Record (depress simultaneously PLAY )
Fig. 2.1-1
B
VU-Meters, record pre-selector buttons Record CH I ( upper track ) : Depress left record pre-selector button Record CH 2 ( lower track ) : Depress right record pre-selector button Record Stereo ( both tracks 1 : Depress both record pre-selector buttons
Power switch, tape speed, tape tension Headphone socket ( 200 - 600 Ohm ) Microphone socket,
11
Fig.
CH 1 CH 2
I \2 1
13
/ \
14
15
I
\
16
/
17
\
18
10 11
Microphone socket, Playback mode switch Balance control
Playback volume control
12 2.1-2
13
Before-and-after tape switch Record volume control, CH 1 lnput selector, CH 1 Record volume control, CH 2 lnput selector, CH 2
I
25
Fig. 2.1-3
1
26
I
27
28 29
30
I
31
29 30 31
RADIO, Dl N connection: lnput 2,5 m V Output 1,2 V OUTPUT ( 2.5 V 1 6 0 0 Ohm ) Socket for power cable
TECHNICAL DETAILS Measured with REVOX 601 tape Tape transport Tape speeds 'Now and flutter : I weighted i Tape slip : Tdpe spool d~amcter Operating posit~on Ampl~fters 3 - motor deck. Electronically governed caElfan motor. Electronic speed change 3 314 and 7 112 ips %at 7 112 ips. max. i .1 % a t 3 3/4 IPS. m;lx.
+ .OB
i .2 '%
less than max.
.2 %
105" veitlcai
Hor~zontal or
Equipped wlth sillcon translrtors throughout. Plug-in pr~nted circu~t cards 30 Hz - 20 kHz 50 Hz - 15 kHz 30 Hz - 16 kHz 50 Hz - 10 kHz
Frequency response via tape
+2 I 3 i 1.5
:; }
}
at
ips.
+ 2 1 -~3 dB
r 1.5
dB
at
3314
Ips
D~stortian tape. a t 1 IkHr vra peak lpvel and at 0 VU respectively Equaiizalion
7 112 Ips. max. 2 '%or 0 6 % rerp. 3 314 ips: max. 3 % o r 1.0 % resp. Record Playback . NAB NAB and IEC si,~,itchable)
Slgnal to noise ratlo. "la tape. we~ghted per ASA A ds Cross talk at 1 kHz : General Measurement Conditions : ( f o r voltages in rectangular frames 1 Osclllvtor frequency Jack Cinch I
7 112 ips mln. 66 dB ( 4 track mtn. 62 dB) 3 314 IPS. mln. 63 dB 14 track mln. 59 d B )
Mono better than 60 dB,
stereo better than 45 dB
120 kHz, push pull osc~llatur
D.C. Voltages . vertical letters e . 9 . P Meter ~nternal resistance 20 kOhm 1V mln. A.F. Voltages: slant l etters e.g. Meter: Vac, rube or transistorvoltmeter 1 MOhm min.
Inputs per channel
Microphone, swltchable LOIHI
5 -pole DIN Cinch
Markings an Tantalum Elecfrolytte Capacttors
LOW: HIGH: RADIO: AUX'
50 600S2 upto lOOkn 33 k n 1 MS2
.15 mV 2.5 mV 2.5 mV mV 35 600 n 2 5 kc1
Red rio'
it, i i
Outputs per channel : Cinch 5pole DIN Jack Remote control
OUTPUT max. 2.5 V 1R s RADIO max. 1.2 V I Rs PHONES 200 600x2
Color dot ~ndlcates+ and multlplter
Fully electilc for all operating functions
IV Output power I 8 load 1 Output impedance Butit in loudspeakers : (portable model 1 Tiana~stors,etc. Two loudspeakers per channel Muslc power 20 W ( 10 W per channel 1 Continuous power 16 W ( 8 W per channel 1 D~stottion better than 1 %
A
Iautamat~callydisconnected when
Color (pink*() black brown
red
1st digit
Worklng voltage IV--10
a plug is inserted Into the DIN loudzpeaker sockets)
-
v
Power supply
fdlalnn voltages
54 trans~tors, 32 diodes, 4 s~licon rectifiers 1 photo resistor, 4 relays Electron~cally stabilized 110. 130. 150, 220, 240, 250 V-I 50 - 60 Hz Without output amplif~err 70 W With o i ~ t p u t amplifters approx. 7 0 100 W
orange yellow green blue violet gray white
35 V " * 6V 15V 20 v
Power consumption
Mans fuses
* **
possibly missihg on model B 35 V on model A p ~ n k
We reserve the right to make techn~cal alterations In the lnterefs of techn~calImDrovements
Dimensions Walnut Cabinet
Dimensions Carrying Case
Dimensions Chassis
Color Code :
red org ye1 grn blu
= red
= orange = yellow
= green = blue
- rouge - orange - jaune - vert
- bleu
vio brn grY blk wht
= violet = brown
- violet
= gray = black = white
- brun - gris - noir
- blanc
3.DISMANTLING
3.2.
-
Removal of Cover Panel
Tilt access lid down. Pull off head cover. - Undo screw A ( fig. 3.2 -4 ). Pull cover panel off ( Upper rim, 3 retainers ). Table of Wire Colors red org ye1 grn blu vio brn gry blk wht
=
= =
=
= = = = = =
red orange yellow green blue violet brown gray black white
rouge orange jaune vert bleu violet brun gris noir blanc
Rot Orange Gelb Grun Blau Violett Braun Grau Schwarz Weiss
Fig. 3.2-4
3.3.
-
Removal of Front Panel
3.1.
-
Removal of Housing
Undo screws B ( fig. 3.2 -4 ). Pull out power switch knob as well as all rotary knobs and discs. Save retaining ring of power switch. - Pull up monitor panel ( 4 retainers).
Set instrument face down on soft basis. Remove remote control dummy plug. - Remove housing fasteners. Pull housing carefully upward. Disconnect loudspeaker connectors on reaulator card ( fig. 3.9 -13 ) in the carrying case. - Reinsert remote control plug. - Bridge power disconnect jack ( 2-pole protective disconnector ) with two insulated banana plugs.
-
3.4.
Removal of Power Switch
- Disassemble retaining ring of slide switch ( equalization switch ) - Unfasten 3 screws. Remove power switch carefully. - Take off plug connectors.
brn CD 1 blu CD 2
blu
red CF 1 wht red
blk
Fig. 3.4
Fig. 3.5-6
3.5.
-
Removal of Brake Unit
3.6.
Removal of Reel Motors
Remove cover panel per 3.2. - Remove reel plates ( 3 screws each ). - Brake drums: Undo center screws A ( fig. 3.5 -6 ), loosen brakes and lift drums carefully upward. Be careful not to kink brake bands. Don't touch brake linings, Grease traces reduce braking effect. - Remove connections 5 ( fig. 3.5 -6 ). - Separate cable bundle ( shielded wires) at G ( fig. 3.5 -6 ) - Remove 3 chassis screws D ( fig 3.5 -6 ) and lift chassis carefully out.
- Remove brake drums per 3.5. - Remove frame screws E ( fig. 3.5-6 ). - Unplug output amplifiers ( if present ). - Unplug motor cable connectors; right reel motor, regulator card ( fig. 3.6-7 ); left reel motor, control card ( fig. 3.6-8 ).
Fig. 3.6-8
Left Reel Motor
Fig.
- Remove 4 reel motor screws F each ( fig. 3.5 -6 ) and lower motors carefully.
3.7.
-
Removal of Capstan Motor
Remove output amplifiers ( if present ). Disconnect capstan-motor and pick-up cables; connections are on control card ( fig. 3.7 -9 ).
E2 nn
Note: For improved signal to noise performance, the capstan motor connections may be reversed on some recorders in the following manner: E3 = gry, E4 = yel, E5 = grn. Carefully note wire colors before disassembling.
Capstan Pick-up
Undo cable clamps A (fig. 3.7 - 9 ) . Remove cover and monitor panels per 3.2. and 3.3. - Unscrew motor fasteners B (fig. 3.7 - 10) on headblock. The other screws on headblock shall not be touched as they retain the headblock itself. - Remove capstan motor carefully downward. Guard absolutely against bumping (axis run-out i s better than .001 mm = 40 micro - inch 1 )
-
Fig. 3.7-9
3.8.
Removal of Control Board
- Remove cover and front panels per 3.2. and 3.3. - Undo screws A ( fig. 3.8-11). Pull control board down -
ward. Remove connectors a needed. s Fig . 3.7-10
A
Remote Control
gry F68
wht FG9 brn FG1
blk FGlO vio FG7
grn F H l Photoelectric End-of-Tape Switch grn FH2 vio D F 4
ye1 D F 2
CID
I I I
) blu FM2
Fig. 3.8-1 1
Left Reel Motor
8
3.9.
-
Removal of Power Transformer
- Remove output amplifiers ( if present ).
Disconnect brake solenoid cables ( unsolder ) per fig. 3.5 -6, B. Disengage cable to right-hand reel motor on regulator board ( fig. 3.6 -7 ). Disengage cable to capstan motor and pick-up on motor control board ( fig. 3.7 -9 ).
N
-
-
Note:
For improved signal to noise performance, the capstan motor connections may be reversed on some recorders in the following manner: E 3 = gry, E4 = yel, E 5 = grn. Carefully note wire colors before disassembling.
, n
- % '
w
w w n S a w
F
-
r
N
m
"
U
a
n
m
E
Z > .
b
r
r
= c z b m 3
"
m
a
m
w
3 n
w
Capstan Motor
Right Reel Motor
Switch Speakers Off
b
ye1 D l 3 grn D l 4 blu (grn/blk) D l 5 brn (yellblk) D l 6 . ye1 u I I
4
grn DG3
blk DG1
I
- a-
org DK3 /
red DG2
ye1 D l 0 red D l 1 grn D9 brn D l 2
I
Speakers Output
I wht D4 0 gry Dl. I wht D3 0 gry 0 2 0
L
r r * N
Fig. 3.9-13
Built-~n Loudspeaker
2 2 :
6
y . g . 2 ~= a z c 7 J = > 23j b?2 > . .
::5$s:
NhlNNFC
5 ' s
-
Unscrews transformer fasteners and remove entire assembly carefully downward. Pull off circuit cards and corresponding connectors as needed (fig. 3.9 - 12 and 3.9 - 13).
3.10.
-
Removal of Amplifier Cards
Mark record and playback amplifiers before removing. The amplifiers have to be reinserted in their respective places to maintain correct level settings. - Remove cover panel on the front side and pull amplifier cards.
Fig. 3.10-14
3.11.
Removal of Potentiometer
( fig. 3.1 1 --15)
- Unsolder wires. - Unscrew fasteners from below
VOLUME
BALANCE
LEVEL
ye1 or9
P 304 CH I I P 303 CH I
ye1
blk
blk brn org red blk red org
red grn
Fig. 3.11-15
3.12.
Removal of Switch Board ( fig. 3.12 -16
- Remove plug-in amplifiers ( fig. 3.10 ). - Remove pusher mechanism ( screws A ). - Remove shield ( screws B ). - Remove reset spring C ( tape lift lever 1. - Connectors: disengage headblock-VU-meter board.
vio HB7,
~ I rise U
grn HB5 ye1 HB4 org HB3 red HB2 brn HB1
--------
-___ uI Ii
FI
=
Fig. 3.12-16
Playback Head CH II
Playback OUTPUT Head CH I
Fig. 3.12-17
Switch Speakers Off
Remove power switch retaining rings and fasteners D. Lower power switch carefully ( avoid linkage rod ). - Disconnect all terminals on the switch board ( fig. 3.12 -17 ). - Unscrews 5 fasteners E ( fig. 3.12 -16 ) and remove complete assembly forward. - Disengage remaining VU-meter connections.
-
Observe, furthermore, that pressure roller is in rest position ( trip lever of playback cut-off contact S 5, left of release lever ).
3.13.
-
Removal of Frame ( Removal of Rotary Switches )
Position of the equalizing slide switch has to be checked at reassembly. Adjust screws F (fig. 3.12 -16 ) if necessary ( see also 5.1. ).
Unscrew VU-meter carrier; l i f t o f f carefully ( observe playback cut-off contact S 5 behind VU-meter board ). - Pull connectors from Jacks. ( fig. 3.1 3-18 ). - Unscrew rotary switch fasteners from above. Disconnect ground strap ( brown ). Remove carrier.
red
bin rkd
Fig. 3.13-18
Phones
Mic I
Mic II
4. MECHANICS
The three-motor drive assures almost maintenance-free service of the mechanical section. Adjustments and measurements are limited to the few movable parts. Special tools needed : Retaining ring pliers Spring scales or contactors 200 g ( 7 oz. av ), 2000 g ( 4.4 Ib. av 1.
4.1.
Headblock
Tape guides
Azimuth Adjustment Record Head
Azimuth Adjustment Playback Head
Don't disturb !
Height Adjustment Fig. 4.1-19
4.1.1.
Tapeguides (fig4.1 -19)
4.1.2.
Head Mounting
( fig. 4.1 -20
- Clean tape guides; don't disturb tape guide A ! To remove tape guide A, unscrew only the fastener to the block ( near upper end of capstan axis ).
Record and playback heads are mounted on a common base plate which is fastened in turn to the headblock with 3 screws A. Don't disturb setscrews D (height adjustment). The heads can be removed while base plate i s off (fastening E). If height adjustment is required after change, the respective setscrews D are turned by a like amount front and back.
/ -
-
B = C =
Azimuth adjustment, record head Azimuth adjustment, playback head
(per 6.5.1.) (per 6.3.1.)
\
----. -
Fig. 4.1-20
12
Once adjustments are made on the headblock, the loosened screws must be resecured with lacquer. Note: For improved signal to noise performance the connections to both playback head channels may be reversed on some recorders from the wiring shown in Diag. 3, in other words the colored conductors will be soldered to the right-hand terminal. When replacing heads, re-wire in the same manner.
Check operating voltages of reel motors and phase shift capacitors if these values aren't attained; see table 5.9 -46 and section " Modifications " per 8.1.( Rewind ).
4.3.
-
Brakes
( Stop )
The stop brakes are effective with solenoid de-energized. Push STOP button.
4.2.
Tape Tension
4.3.1. Brake Torque Measurement
Preparation for measurement per 4.2. Correctly set brakes have following torques:
- Cover light at the optical end-of-tape switch. Measurement values are taken on a core of diameter 115 mm ( 4 , 5 " ). - Load and lock empty reel.. - Wind several turns of thread on empty reel and pull thread off slowly in the sense indicated, resulting in the following values:
@
115 rnrn
L
-------1
Fig.
Fig. 4.3-23
Function 7.5 ips or 3.75 ips
A
B
/ 1
PLAY PLAY
1 1
tape tension, high tape tension, low
I 70gri
( 2.5 oz.av
( 3 oz.av ) 85gr
I
4.3.2.
Brake Adjustment
about 20 gr
Check brake system if above mentioned torques are not reached. Brake linings and bands must be absolutely clean and free of grease. Brake bands must be devoid of kinks and lay up full-width on lining. Details on the modified brake system (brake return spring attached to both ends of the brake-band) are shown on page PL 7a of the parts list. Brake mechanism and solenoid stroke are reset after exchanging band and/or linings.
Table 4.2-22
Fig. 4.3-24
I
- Loosen brake manually ( push in solenoid core ). - Check if both brakes clear simultaneously; if not unscrew the 3 chassis fasteners partly, slide chassis around till both bands are clear. - I f necessary, bend one brake adjustment lever.
The solenoid has to be energized for adjustment. - Cover light at the optical end-of-tape switch. - Depress " Reel Motors off " ( 42 ), depress button < < ( fast rewind ). - Loosen fastening of solenoid and reset so that the bands clear rollers by from .I -.2 mm ( 040" to . 080" ) - Secure solenoid during this adjustment. Braking torque can be varied by hooking springs at different places on the brake adjustment lever.
4.4.2.
Pressure Solenoid Readiustment
.
- Switch instrument to PLAY. I f no tape is loaded, cover light at optical end-of-tape switch. - Slide pressure solenoid to the right gap B (fig. 4.4-25) is .3 mm ( ,012 " ) - Block pressure solenoid. - Check if .solenoid core is in end position. The core shall not move if the lever is pulled slightly from the capstan axis. - Secure fasteners of solenoid with a drop of lacquer. - Check pressure, reset screw C if necessary.
4.4.3.
Exchange of Pressure Roller
4.4.
Pressure Roller
The pressure lever is actuated electromechanically. Pressure is set by the variable spring force ( fig. 4.4 -25 ).
- Hold pressure roller axis at groove from above ( fig. 4.4 -25 ) and remove bolt fastening E to the side. - Pull pressure roller axis up and roller to the side. Reassembly is explained in the replacement parts list.
Make sure that no cleaning fluid gets to the sintered bearing while cleaning the roller.
4.4.1.
-
Pressure Measurement
Load tape with 1 kHz record. - Switch on PLAY. - Tie nylon thread to pressure roller axis ( or to a pin affixed thereto ) and pull with a spring scale ( or contactor) in sense A till sound volume drops noticeably. The spring scale must show 1.5 kg ( 3.3 Ib. av ). - Screw C sets pressure force.
I
4.4.4.
Pressure Lever Readjustment
After exchanging the pressure lever, it is necessary to readjust i t with respect to lever F ( fig. 4.4 -25 ). When the lever is stopped ( solenoid core fully out ), the distance between capstan axis and pressure roller shall be 10 mm ( .4 " ).
---
--
Fig. 4.4-25
A
1.5 kg ( 3.3 Ib.av )
B
0 3 mrn .
( 012" )
( Mobil
Fig. 4.5-26
ATTENTION Capstan Motor with Sleeve Bearings Modification effective from serial Nr. S 60483 G 78003 see section 8.6.lpage 35 4.5. Capstan Motor (with Ball Bearing) Fig. 4.5.-26 (Control circuitry see 5.10 & 6.2. ) The capstan axis goes cornplere:y through the motor. I t is held by a sintered bronze bearing ( D ) and below by a ball bearing. Both bearings are lubricated for their life and should normally require no service. Capstan axis and ball bearing can be exchanged very easily. A defective sintered bearing is to be sent to the nearest factory representative. ( Disassembly see para 3.7. )
-
- Unfasten securing clip A. Lower capstan rotor. The axis can be taken out through the top if the tape guide between playback head and capstan axis has been screwed off ( don't disturb guide setting ). - If the retaining ring B is removed, the capstan axis can be lowered with bearing C.
Bearing C is a special tight tolerance part and shall be exchanged only with an original bearing. Special care must be taken with handling the capstan axis and bearings to avoid damage or entry of dust into the precision parts ( run-out better than 1/1000,mm = 40 micro - inch ! ).
4.5.1. Removal of Capstan Axis, Ball Bearings The capstan motor need not be removed to get axis and bearing out.
Instructions for installation of the new no-turn device A in conjunction with old rotors are given on page PL 9 of the parts list.
4.6.
Exchange of Reel Motor Bearings
- Remove reel motor per 3.6. - Remove brass sleve A. Open clip B and retaining ring C with retaining pliers, open only wide enough t o pull them away. Lower rotor with axis out of motor frame.
The belleville springs (see parts list PL 8) remain on the shaft.
Fig. 4.5-27
In addition to sleeves A there are washers D for height adjustment of the brake drum ( reel plate ). Be sure t o put these parts on the same motor axis at assembly. The reel motor ball bearings shall exchanged only with original bearings.
4.7.
Lubrication
All bearings are lubricated for their life and should normally require no service. They shall be exchanged only with original bearings, in case of malfunction. I f the capstan axis is exchanged, the upper felt washer of sintered bearing D ( fig. 4.5 -26 ) is to be lubricated with some drops MOB1L DTE extra heavy.
4.8.
End-of-Tape Switch
( Operation: per 5.9.1. )
The light source of the optical end-of-tape switch can be removed by lifting it upward.
5. ELECTRONICS
Plug-in Output Arnpl.
Regulator
Power Supply
The electronic circuitry is divided into groups, plug-in modules for the most part. There are etched circuit card plug-in modules for :
-
Input amplifier, record amplifier, playback amplifier, oscillator, and record relay. Output amplifier.
There are several etched circuit boards, rigidly mounted but with plug-on connectors for:
- Regulator - Drive control with photoelectric - Capstan motor control.
end-of-tape switch.
Plug-in Arnpl.
/
Capstan Motor Control
I
Drive Control
I
Block Diagram
( Amplifiers
Fig. 5.-28
The block diagram shows the relationships between the plug- in amplifiers.
INPUT NAB
CH I
SPEMLRS
Volume
CHll
OFF
5.1.
Switch Board and VU-Meter Board
( Diagram No. 1.077.435 & 1.077.480 )
( Removal per 3.12 )
'The switch board carries plug-in amplifiers ( without output amplifiers ), control switches and potentiometers for inputs, balance and volume. The shielded inputs can be plugged on the switch board ( below, left-hand ). Inputs for playback amplifiers as well as outputs for OUTPUT and output amplifiers can also be plugged in ( right-hand 1. The equalization slide switch i s controled through the power switch. I t has to be readjusted in case of exchange. This i s done with screws F ( fig. 3.12 -16 1. The s ~ ~ l t c l i termlnal coritdct areds for tripui selector, beforeand-dfter tdpe swltcli, and playback functions are pr lnted dlrectly on the board. The rotary sw~tches are encased and indexed agacnsl rrilsortentatlon. Check flg 5.1 -32 for case and contact conf~gurat~ons Assembly lnformcltlon I S ~n the spare parts list.
7 - i
__.
1
-
--
Fig. 5.1-30
Inputs
CH ll
Inputs CH I
iz
a m -
.s
y l
Lamp, end-of-tape switch
g2
Playback Head CH I I Playback OUTPUT Head CH I
-
7
>
r
N
+
Switch Speakers Off
Fig. 5.1-31
Before / After Tape switch ( Playback selector Fig. 5.1-32
Playback Mode Switch
lnput selector
The VU-meter board is linked to the switch board by connectors. It carries the preselector buttons for CH 1 and CH 2; they switch the record-erase signals. ( Note that the audio signal has to be switched inversely on the record amplifier when neither button i s depressed ! )
*blu -gn ,r --ye1
I
vio HB7 HB6 HB5 HB4 HB3 "red HB2 I 'brn HB1
I
+erg
I
1
1
CH I CH II
( 1.077.700 )
-I
Resistor R 406 / R 426 ( lOOK ) i s bridged or reduced by parallel resistors for this purpose. If R 406 / R 426 is shorted,amplification of the whole stage i s A = 460 approx with 1K in parallel A = 20 approx, and without parallel resistor A = 1.2 approximately. Parallel resitors R 316 / R 317 ( CH 1 ) and R 321 / R 322 ( CH 2 ) are on switch board 1.077.435. The output stage configuration has the advantage that the supply voltage can be fully modulated. Output voltage i s nominally 50 mVac, but it can deliver up to 6 Vac undistorted. This corresponds to an overmodulation stability of more than 40 dB. Aside from the overmodulation stability, sensitivity matching of the input stage through feedback has the advantage in that input noise i s not worsened by the series-connected voltage divider.
Fig. 5.1-33
5.2.
Input Amplifier
5.3.
Record Amplifier
( 1.077.705 )
Fig. 5.234
Fig. 5.335
The input amplifier card contains the pre-amplifiers for both channels. Input sensitivity is matched through a stepped variable feedback (d.c. feedback fixed) at the signal source voltages AUXILIARY ( 35 m V ) , track transfer ( 8 mV ), RADIO ( 2,5 mV 1, MICROPHONE high (2,5 mV 1, MICROPHONE low ( .15 mV ).
The record amplifier cards contain an equalization preamplifier ( Q 501, Q 502 1, a VU-meter amplifier ( 503 ), and a driver amplifier ( Q 504, Q 505 ). A t the input of the equalization preamplifier is a bus voltage level of about 25 mV at 1 kHz and nominal input signal, record regulator fully opened ).
Recording is equalized per NAB standard. Lows equalization ( 3180 ysec ) i s accomplished by feedback through series-connected C 504 and trimpotentiometers P 501 and P 502. Highs equalization can be set separately for both speeds; P 502 for 7.5ips, P501 for 3.75ips. Trimpot P 503 serves for voltage balance. The driver amplifiers are laid out for high overmodulation stability. Transistor Q 505 supplies the necessary collector d.c. to Q 504 for modulation. Q 505 represents high impedance for AF which furnishes the entire output a.c. for modulating the record head. Modulation reserve i s -better than 15 dB. A tank circuit with a resonant frequency of 38 IkHz causes current depending feedback in the emitter circuit of the driver stage ( L 502 I 514 1 for pilot carrier remainders which could C interfere with the erase frequency. Between the decoupling point and record head is another tank circuit for the bias of 120 kHz ( L 501 1 C 517 1. The decoupling point is shorted by the record relay during playback. Amplification of the VU-meter stage can be calibrated on P 504. To protect the VU-meter indicators a9ains.t RFl ( radio frequency interference 1, resulting in misindication, the stage is decoupled for R F with C 508.
5.5.
Record Relay
( 1.077.7 15 )
Fig. 5.5-37
Purpose of the record relay with an electronic switch i s to turn on the oscillator " softly ". T o get an integral curve of the switching voltage, Q 601 ( switching transistor ) is delayed by an RC - network ( R 603, C 602 ).
5.4.
Oscillator
( 1.077.710 )
Fig. 5.5.-38
C 602 is discharged at the start and the base of Q 601 is at OV. If contacts 213, 516 of record relay REL 601 close, bias voltage rises with the charge o n C 602 till saturation. Wihen contacts 213, 516 open, C 602 discharges over R 602. The head compensation coil has two winding halves acting as dummy load for the inactive half o f the erase head during mono-operation. The compensation coil balances out inductive strays of the erase head. Resistor R 604 corrects 0 - factor and assures minimum voltage jump between monaural and binaural operation ( exchange of erase head may require resetting ).
Fig. 5.4-36
The push-pull collector circuit guarantees minimum odd harmonics. Symmetry of sinusoidal waves is assured and interfering d.c. components can't arise. Erase and bias of 120 kHz is high enough to prevent their interfering. The erase frequency is symmetrically decoupled. In mono-operation, load i s held constant by the compensation coil ( para 5.5. ) which proves advantageous for voltage and frequency stability. Bias current can be set with trimpots P 707 to P 710 separately for CH 1 and CH 2 as well as for both tape speeds.
5.6.
Playback Amplifier
( 1.077.720 )
CH I I Fig. 5.6-39
CHI
Playback amplifier cards each contain one playback ( pre- ) amplifier and one drive amplifier. The playback head is d.c. coupled to the input stage ( Q 801 ). D.c. feedback from the emitter voltage divider of stage ( Q 802 ) goes over the playback head to base ( Q 801 ) and stabilizes its quiescent point. The feedback current i s less than 1 p A which avoids magnetization of the playback head. AF-components of the feedback are shunted through C 803. Its capacitive resistance becomes effective at very low frequencies ( less than 20 Hz ) so that these frequencies are fed back. Playback equalization i s switchable NAB I EC ( CCl R ). The equalization circuit is in the feedback branch collector Q 802 / emitter Q 801. The RC-member R 808 / C 805 / takes care of the lows equalization (3180 psec 1. Basic time constants of equalization are obtained by shorting the partial resistors of the circuit. For : 7.5 ips 3.75 ips NAB I EC NAB / IEC
( 50 psec ) ( 70 psec )
( 90 psec )
The power amplifier cards have separate rectifiers and filters for each channel. The power transformer has two separate windings ( 32 Vac ) for the power amplifiers. The entire amplifier i s d.c. coupled and works with a singleended push-pull output stage. The loudspeaker is, practically free of d.c., in the diagonal o f a bridge formed by Q 905 and Q 906 as well a the electrolytic capacitors s C 907 and C 908. Q 901 and Q 902 operate as voltage amplifiers. Series connected D 901, R 91 1, D 902 are used t o keep the no-load current of the output transistors constant, independent of temperature. By strong d.c. depending feedback ( 100 % ), collector Q 906 errlitter O 901, the zero point of the loudspeaker output is held constant. AF-amplification is set by the voltage ratio R 905 to R 906.
3 3
-
4 - 5 4 4 - 5
5.8.
Power Supply
( Diagram Tape Drive 1.077.100, No. 1.077.540) ( Removal, per 3.9. )
A t the pre-stage exit i s a 120 kHz tank circuit for the bias frequency and trimpot P 801 for setting the level of the bus voltage. The signal is conducted over the beforeand - after - tape switch, volume control, and playback mode switch (channel selector ) to the drive amplifier. The drive amplifier is three-stage d.c. coupled. I t amplifies the signal to the level of the terminals OUTPUT, headphones, as well as for the modulation of the plug-in power amplifiers. D.c. feedback, emitter voltage divider Q 804 / base Q 803 stabilizes the quiescent points of all three stages. Balance regulation is accomplished with potentiometers P 303, P 304 ( coupled ) in feedback branch emitter Q 805 / emitter Q 803. In STOP position, when the pressure lever is at rest, output of the playback pre-amplifier ( 13 ) is shorted through contact S 5 ( switch board 1.077.435 ).
Both lines of the power supply can be switched off ( MicroSwitches ). In addition there are two break-contacts which disconnect upon removal of the housing. The sectional tape core power transformer has five windings for following units : Capstan and reel motors: Relay control : Amplifier supply : 130 Vac 22 Vac 24 Vac (150 Vac) with 4 taps
( supply voltage 27 Vdc) ( supply voltage 21 Vdc,
regulated ) Output amplifier : Output amplifier : 32 Vac 32Vac (CH 1 ) (CH2)
5.7.
Power Amplifier
( 1.077.850 )
Fig. 5.7-40
Fig. 5.8-41
Power supply board 1.077.540 carries the output amplifier connectors. The electronically regulated voltage (21 V ) for amplifiers (and oscillator) is adjusted at P 106. The transistor Q 102 acts as a series regulator, whose conductivity i s controlled by Q 101. The zenerdiode D 104 provides a 12 V reference for the emitter of this latter transistor. Diode D 103 protects the base-emitter diode of transistor Q 101 from overload in case of possible short circuit in the amalifier section.
5.9.
Drive Control
m
PHOTO-ELECTRICAL END-OF-TAPE SWITCH
( 1.077.370, Diagram Tape Drive 1.077.1 00 )
( Removal per 3.8. )
@5
Fig. 5.9-43
L
-
If button << is depressed, relay A i s shorted and drops off. Simultaneously relay B i s energized and holds itself over self-holding contact b 6/10. Self-holding can be interrupted by the STOP button or by the photoelectric end-of-tape switch. The following table indicates which relays and solenoids are energized for corresponding functions.
Table 5.9-44
Fig. 5.9-42
The drive push buttons operate contacts on control board 1.077.370. Remote control contacts can be paralleled to these contacts ( remote control contacts F3 to F10 ). To have a minimum of relays, their control i s locked by diodes. The principle of their control i s explained by an example for better understanding. In the circuit of fig. 5.9 -43, relay A is energized and contact a 8/12 ( self-holding ) is closed. This corresponds to mode PLAY. Relay B i s without current, contact b 6/10 is open.
To avoid loose tape loops at record and playback starts, the right-hand reel motor receives elevated voltage for about 0.3 sec ( winding reversal voltage 105 V ). Relay C must be energized a short period for this, accomplished by the following circuit :
ROLLER SOLENOID BRAKE SOLENOID
Fig. 5.9-45
22
If the instrument is in the STOP mode, relay A i s without current and contacts a 12 and a 11 are in rest position ( fig. 5.9 -45 ). If relay A is energized ( PLAY mode ), i t will hold over self-holding contact a 8/12. Contact a 7111 closes. A charging current to capacitor C 11 1 flows over the relay. This energizes relay C and switches the right-hand reel motor to 105 V over contact c 519 ( self-holding relay C i s interrupted by contact a 12 ). The charging current falls with increasing charge on C 111 and relay C drops off. When switching back to STOP mode, contact a 7111 opens and capacitor C 11 1 discharges over the windings of brake and roller solenoids.
The process is accelerated by the falling emitter voltage on R 119 (feedback ), so that a pulse-type transcient occurs despite the gliding resistance change of R 155 ( sensitivity inertia ). The trigger conditions light - dark, generate the following voltages at collector 0 11 1: light, 1 V; dark about 22 V. To check the photoresistor, for light and dark values, it must be disconnected from the circuit. Connections F H I / FH2 ( green ) on switch board ( fig. 3.8 -1 1 ) have to be pulled for this. The resistances are: light, less than 2 kOhm; dark more than 20 k0hm. ( Don't solder at the soldering terminal of the photoresistor, it i s heat sensitive ).
The following table summarizes motor voltages for the drive modes.
5.10.
Speed Regulation, Capstan Motor ( 7.077.725 )
( Removal per 3.9. )
I
Mode
1
Motor Voltages in Vac Rewind Motor
I
Winding Motor
The electronically regulated tape drive of REVOX A77 uses a method unknown so far in tape recording. That is why this technology of regulation is described here rather detailed. Checks and adjustment of the regulation electronics are done per 6.2.
Table 5.9-46
5.9.1.
Photoelectric End-of-Tape Switch
The working current loop of the relays is closed over the self-holding contacts, the STOP button and the collectoremitter path of switching transistor Q 112. Triggering the end-of-tape switch ( Schmitt-trigger ) does the same thing as depressing the STOP button. As soon as light falls on photoelement R 155, its resistance drops and base voltage at 0 111 rises. Collector voltage at Q 111 drops and cuts off Q 112.
Fig. 5.10-48
+27V
TO RELAYS A, B AND C SELF-HOLDING CONTACTS
r-!
The capstan motor speed is electronically measured and continously regulated. The driving element is a robust and unpretentious asynchronous motor, whose homogeneous outer rotor generates a minimum of torque pulses, reflected in scant wow or flutter. To measure the speed, a 120-teeth high-precision gear is cut into the outside surface of the rotor. They are inductively counted by a special pick-up head. The speed is then transformed into a proportional frequency which is analyzed for momentary value in an electric circuit. Any deviation from the nominal, 1600 Hz f o r 7.5 ips and 800 Hz for 3.75 ips, is detected as to magnitude and sign, and changes the voltage applied to the motor. The actually regulating network ( fig. 5.10-49 ) consists of a bridge rectifier in series with the supply, whose diagonal is loaded more or less by a power transistor. A power transistor with nearly constant base current doesn't show a genuine resistance characteristic ( I - V ), for it acts as current control element.
Fig. 5.9.-47
= &
130 V- (150 V-)
The series potentiometer P 201 allows detuning the resonant frequency slightly. This permits calibration of the speed separately. The high speed is set by adjusting primarily the circuit's inductivity. Fig. 5.10 -50 shows the voltage characteristic as a function of frequency for the whole discriminator. The operating range of the following d.c. amplifier is given for clarification. The discriminator is temperature compensated along with the entire circuitry. Fig. 5.10 -51 shows the typical thermal characteristic of the whole system, measured inside the climatic chamber while motor was running.
3
CAPSTAN
MOTOR
I
ti?
I
ov-
1604
I
T---
Fig. 5.1 0-49
Circuit 1.077.725 consists of tachometer signal amplifier
( Q 201 to Q 205 ), the discriminator, and d.c. amplifier with power stage ( Q 206 to Q 209 ). The tachometer
signal amplifier amplifies, makes symmetrical and limits the pick-up frequency to supply square wave pulses to the discriminator. D.c. dependent feedback stabilizes the quiescent points of the amplifier stages. The discriminator consists of an LC-series-resonance circuit of utmost constancy due to type of circuit and components used. Best drift characteristics are essential to guarantee the required maximum speed variation of .2 % !
Fig. 5.10-51
The discriminator frequency can be changed from 1600 Hz t o 800 Hz by switching in capacitor C 207. In addition, diode D 201 is polarized in conductive direction, thus requiring at the control side but one low current contact, it also decouples the control line ideally.
v
The signal, delivered from the discriminator, i s stripped of a.c. components from the tachometer frequency by integration ( C 210 & C 21 1 ). The R 215 - C 209 member corrects phase error in the control circuit and improves stability. D.c. amplifier Q 206 - Q 207, whose operating range is shown in the discriminator characteristic, has an amplification of 40 dB. I t brings the signal t a the value needed for power amplifier Q 209. The phasb inversion stage Q 208 has little amplification. Power stage Q 209 consists of a transistor which resists those peak voltages that can occur during cut-off and i s able to conduct the power loss, generated during operation, onto the heat sink.
Operating Range
F
Some interesting system data :
1. Steepness of the discriminator and amplification factor of the following amplifier cause the motor voltage to traverse from 0 Vac to the maximum value 130 Vac within 3 Hz frequency deviation at the 1600 Hz tachometer signal frequency. This means that the motor receives full or no voltage for a percentage deviation of +.I%.
Fig. 5.10-50
2. Line voltage variations of 20 % cause a deviation in speed of the order of k .04 %. 3. Variations k 10 % in operating voltage 21 V, cause a deviation of speed by +.I % ( operating voltage is additionally regulated 1.
4. Changing the supply frequency from 50 to 60 Hz varies motor speed by less than .05 %. Point 4 shows that the supply can be alternated between 50 and 60 Hz with absolutely no changes in circuitry. The new motor is considerably lighter than synchronous motors were to date. I t has neither flywheel mass nor a soft clutch. The capstan axis is rigidly fixed to the rotor, making interchanges very easy. The relatively low speeds of the capstan motor ( 400 and 800 rpm ) provide a large diameter capstan axis.
Notes
6. ELECTRICAL ADJUSTMENTS AND MEASUREMENTS
6.2.3.
Tacho Adjustment with Cathode-Ray Oscilloscope
Measurement Instruments and Aids
If need be, adjustments can be made with an oscilloscope referenced to the 50 Hz network frequency test point D ( diagram 1.077.725 ) there is ( closed to OV ) an a.c. signal of 100 Hz of the following shape :
-
Demagnetizing coil AF-millivolt meter or VTVM ( vacuum tube voltmeter ) AF - generator Distortionfactor meter Oscilloscope or digital counter Wow and flutter meter
- Test Tapes
( Reference Tape )
Test tapes per NAB ( 1965 ), and DIN Heimton 7.5 ips ( 1966 ) and 3.75 ips ( 1967 ) are equalized alike for respective speeds. 7.5 ips
= 3180 psec, 50 psec test tape DIN 45513
/ 19 H
/9
( f r o m AGFA or BASF ) or NAB 7.5 ips. 3.75 ips
= 3180 psec, 90 psec test tape D l N 45513
( f r o m AGFA or BASF ) or NAB 3.75 ips ( 90 psec ).
The superposed frequency comes from the regulating system and is 1600 Hz for 7.5 ips, 800 Hz respectively for 3.75 ips. Measurement i 5 accomplished in the PLAY mode with tape in place. The superposed frequency must remain standing with respect to the base frequency ( a t 50 Hz network frequency ). ( Adjustment procedure per 6.2.2. )
- Adjustment Tape 4 - track ( .25
"
)
for height adjustment of the magnetic head on 4-track instruments. A l l AF and R F measurements are to be talcen with shielded cables.
6.3.
Playback Adjustment
Preparation : Check regulated supply voltage ( 21 V ). Apply corrections t o P 106 t Power Supply Card 1.077.540 ).
6.1.
Demagnetizing
- Magnetic heads and tape guides are to be demagnetized before any measurement or adjustment with running tape.
Strong d.c. - magnetization disimproves signal-to-noise ratio and frequency response. I t can also permanently damage the test tapes.
Check of Balance Adjustment :
- Connect AF-generator to AUX-input. - Parallel the signal voltage on both inputs by bridging the solder terminals of the AUX cinch-connectors with alligator clamp. - Set controls per fig. 6.3-52
,HAN.,LL 8
6
6.2. 6.2.1.
Tape Speed Pick
( Regulator Card 7.077.725 )
- up Head -
Adjustment
,,ANNr,
8,
The air-gap between pick-up head and rotor shall be .3 .4 mm ( .012" - .016" ). Adjustment is correct when a 35 50 mV tachometer signal voltage i s measured ( at 3.75 ips ) on connections blu E2 and brn E l of the regulator card.
RECORD
6.2.2.
Tacho Adjustment
Exact adjustment of the discriminator, respectively of the capstan motor speed, can be accomplished only with a digital counter.
- Connect digital counter t o blu E2, brn E l . - Switch recorder to PLAY ( with tape in place ). - For 7.5 ips, the frequency must be 1600 to 1601 Hz. Measurement time 10 sec. minimum. Apply corrections to core of discriminator coil T 201. - For 3.75 ips, the frequency must be 800 to 801 Hz ( 7.5 ips adjustment has to be made first ! ) - Apply corrections to trimpot P 201.
Fig. 6.3-52
- Measure
- Supply about 30 mV / 1000 Hz. signal voltages at the OUTPUT ( 2 V approx ). Both outputs shall have same signal voltages. Apply correction with the balance control for voltage differences at less than 3 dB at the outputs. Check the amplifier channels if the voltage differences are larger. - Don't readjust the balance control. .
6.3.1. Azimuth Adjustment, Playback Head, Coarse
( Max. Level )
( Assembly and coarse adjustment after head exchange per 4.1.2. ) Check of gap centering with respect to polished face :
Switch t o PLAY and set output voltage to a maximum ( sharp ) with screw C. - Secure screw C with a drop of lacquer.
-
- Mark polished face with grease pencil. Let tape run short time. The gap must be in center of worn area. - Set controls per fig. 6.3 -53.
6.3.3. Playback Level from Test Tape
-
Set controls per fig. 6.3 -56.
MONITOR
CH 8
MA0
SECOPD
Fig. 6.3-53
Fig. 6.3-56
Load 7.5" test tape and advance t o azimuth adjustment portion ( 10 kHz ). - Connect AF-millivoltmeter to an OUTPUT terminal. - Switch t o PLAY and set output voltage to a maximum with screw C ( fig. 6.3 -54 ).
-
- AF-millivoltmeter remains connected to one output ( 3 V range ). - Advance test tape to level portion. - Set playback mode switch to CH 1. - Set output voltage 2 V with trirnpot REPR LEVEL CHI ( fig. 6.3 -57 ).
Fig. 6.3-57
Set playback mode switch to CH 2. - Set output voltage 2 V with trimpot REPR LEVEL CH 2.
-
Fig. 6.3-54
6.3.2.
-
Azimuth Adjustment, Playback Head, Fine ( Phase Method )
6.3.4. Frequency Characteristic, Playback
( from Test Tape )
Set controls per fig. 6.3-55.
- Set controls per fig. 6.3.-58.
MONITOR
RECORD
Fig. 6.3-55
Fig. 6.3-58
- I t is absolutely essential to accomplish the coarse adjustment per 6.3.1. before using this method to avoid phase errors larger than 90".
Advance to frequency run portion of DIN or NAB test band. - AF-millivoltmeter, range 300 rnV ( -20 dB 1. Both channels can be measured simultaneously by changing back or forth between each frequency section ( CH 1 / CH 2 1.
-
6.4. 6.4.1.
Oscillator and RF - Adjustments RF - Voltages and Frequency Checking
- Set controls per fig. 6.4 -59
MONlTDR
C",
'"8, W'B
RECORD
Fig. 6.4--61
Fig. 6.4-59
-
Load tape and switch to RECORD ( STE RE0 ).
A. - Measure erase head voltage against ground with VTVM at VU-meter board ( fig. 6.4 -60 ) orange HB3 ( CH 2 ) and blue HB6 ( CH 1 ).
- Depress record pre-selector CH 2 and disengage CH 1. Connect oscilloscope or digital counter t o orange HB3. - Correct DUMMY LOAD if necessary.
2 4 -
Track Track
= =
21 Vac each
16 Vac each
- Repeat adjustment procedure until any remaining frequency deviations are symmetrical around the nominal frequency ( e.g. CH 1 + 1 kHz, CH 2 - 1 kHz ).
1 1 1
blu HB6
org HB3
-
6
1 1 1 1
_ s . l
-..?--3
1 1 1
n
u
6.4.3.
RF - Traps, Record
- Set controls per fig. 6.4 -62
I
MONITOR
RECORD
Fig. 6.4-60
6. Oscillator Frequency - Load tape, switch t o RECORD ( STEREO 1. Pull out lamp at optical end-of-tape switch if measuring without tape. - Oscillator frequency is measured with digital counter or oscilloscope. The frequency is 120 kHz ( + 5 kHz ) and is measured at orange HB3 and blue HB6 (fig. 6.4 -60 ) against ground. ( Oscilloscope: 12 oscillations per 100 psec ).
Fig. 6.4-62
-
Load tape, switch to RECORD ( STEREO ). Connect VTVM t o test point C 515 of the respective record amplifier ( fig. 6.4 -63 ), see also diagram 1.077. 705.
6.4.2.
Dummv Load
The dummy load compensation is needed only when the erase head is replaced (balance of inductive strays from the erase head during MONO - operation ).
-
Record Amplifier
1.077.705
Load tape, switch t o RECORD. Connect digital counter or oscilloscope to blue HB6 ( fig. 6.4 -60 ).
CHANNEL,
8 HaNN-8
,,
- Measure RF-frequency in stereo mode. - Disengage record pre-selector CH 2 and balance DUMMY LOAD till same frequency is reached as in stereo mode.
Fig. 6.4.-63
-
Set minimum voltage at BlAS TRAP CH 1 and CH 2: Less than < 300 mV ( fig. 6.4 -64 1.
- Set AF-generator to 10 kHz ( see 6.5. preparations ). - Load tape and switch to RECORD. - Adjust for maximum signal w i t h screw B ( fig. 6.5 -67 ), ( turn slowly - indication delay ! ).
.m e.
CHI
. L
.
L
:EEL
C ..O )
C" 2
13
C"2
RECORD IMP111
RFOSODUCr & l P L i i l S P
a
E
: %
)
i - - Playback I --
a
,*- (>I
r :
0 13;: 0 :
:EEL
: :, b'
Record
Fig. 6.4-64
6.4.4.
RF - Traps,
Playback
- Under same conditions as 6.4.3. but, connect VTVM to OUTPUT terminals CH 1 and CH 2 and set BlAS TRAP of playback amplifier to a voltage minimum : Less than < 50 mV ( fig. 6.4 -64 ).
Fig. 6.5-67 6.5.2. RF - Bias
6.5.
Record - Adjustments
Preparations : Following measurements ( 6.5.1. to 6.5.6. ) are to be taken with a record level of - 20 dB below full modulation level. ( To avoid over-modulating high frequencies ).
-
Set controls per fig. 6.5 -65.
Since the high frequency playback voltage is bias dependent in a curve with distinct maximum, a relationship which can be used t o determine the operating point ( fig. 6.5 -69 ). The measurement is per 6.5.1. ( 10 kHz, -20 dB 1. Controls OSCILLATOR CH 1 and CH 2, 3.75 and 7.5 ( fig 6.5 -68 ) are turned from the left limit in clockwise fashion until maximum AF output voltage is reached ( playback mode switch by choice CH 1 / CH 2 ).
MONlTO*
,W*"T
RECORD
Fig. 6.5-65
- Connect AF-millivoltmeter to OUTPUT terminal. - 300 mV range - Adjust AF-generator ( 3 - 4 mV ) at 1000 Hz to obtain 200 mV at the OUTPUT terminal ( voltage as for playback from test tape per 6.3.3, but 20 dB lower ).
Fig. 6.5-68 Note the pointer deflection at the maximum and continue turning in the same sense till AF-output voltage has dropped by the amount ( AV ) shown in the following table.
. .
6.5.1.
Azimuth Adjustment, Record Head, Coarse
10 kHz
I
max
- Set controls per fig. 6.5 -66.
MONITOR
RECORD
Fig. 6.5-66
Fig. 6.5-69
29
-
-
Load tape, switch to RECORD ( Stereo ). Before-and-after-tape switch to I NP. Supply 1000 Hz from AF-generator, set generator level such that OUTPUT terminal voltage is 200 mV. Switch to NAB and adjust REC LEVEL trimpots ( fig. 6.5-72 ) to obtain 200 mV at OUTPUT terminal, playback mode switch to CH 1 or CH 2 respectively.
ASF PES 35 (LH COTCH 202 2
Table 6.5-69
6.5.3.
Azimuth Adjustment, Record Head, Fine
Set controls per fig. 6.5 -70 Fig. 6.5-72
RECORD
6.5.5.
Record Equalization
- Switch AF-generator at samevoltage (-20 dB) to 12 kHz.
-
Set controls per fig. 6.5 -71 ( NAB
1.
Fig. 6.5-70
The balance regulator must be set accurately ( per 6.3, preparations ). - Other conditions as up to now ( Record, Stereo, 10 kHz, - 20 dB ). - Set output voltage t o a maximum ( sharp ) with screw B ( fig. 6.5 -67 ) turn slowly - indication delay ! ). - I t is absolutely essential to accomplish the coarse adjustment per 6.5.1. before using this method t o avoid phase errors larger than 90".
-
Fig. 6.5-73
-
Control possibility :
Pass through lower frequencies with sound generator. Output voltage shall remain constant. - Secure setscrew with a drop of lacquer.
Adjust output voltage from 0 to + 1 dB with trimpots EQUALIZ. ( 0 dB = 200 mV / 1000 Hz per 6.5.4 ). Playback mode switch CH 1 both speeds, likewise CH 2 both speeds.
6.5.4.
-
Record level
6.5.6.
Frequency Characteristic via Tape
Set controls per fig. 6.5 -71
RECORD
- Set controls per fig. 6.5 -71 ( NAB ) . - Calibrate AF-millivoltmeter ( change slightly the signal voltage till 0 dB or even-numbered indication is reached ). - Measure frequency characteristics 7.5 ips and 3.75 ips ( by changing playback function switch CH 1 / CH 2, both channels can be measured, one after the other ).
@
MIX
6.6.
Distortion Factor Measurements VU-Meter Calibration Noise Measurement Erase Attenuation Crosstalk Attenuation
Fig. 6.5-71
- Playback level ( per 6.3.3. ) and balance adjustment ( per 6.3. preparations ) must be set. - AF-generator to AUX-input (connect in parallel ). - AF-millivoltmeter to one OUTPUT terminal, range 300 rnV.
6.6.1.
Distortion Factor ( via Tape ), VU-Meter Calibration
- Set controls per fig. 6.6 -74.
Effective values (weighted, CClF filter) of the noise and external voltages can be seen for the REVOX 601 tape in the following table:
MONITOR
RECORD
2 Track 7.5 ips 3.75 ips
1
4 Track
7.5 ips
(
3.75 ips
Noise Voltage Ext. Voltage
Fig. 6.6-74
> 66 dB > 63 dB > 62 dB > 59 dB > 58 dB > 57 d B > 56 dB > 54 dB
Table 6.6-77
- AF-generator ( 500 Hz ). Switch 20 dB higher with respect t o previous setting ( input voltage about 40 m V )
Connect distortion factor meter to an OUTPUT terminal. Load tape, switch to RECORD ( Stereo) 7.5 ips. - Measure distortion factor ( CH 1 and CH 2 ). - Set input level so that the distortion factor is 2 % on the worse channel a t 7.5 ips. - Repeat procedure with 3.75 ips. Distortion factor may be 3 %. In case of higher values, reduce input level till 3 % distortion factor is achieved. - Distortion factor control " Before-tape '? Set before-and after-rape switch to INP. Distortion factor shall be 1 % maximum ! - Switch back to NAB lower input level by 6 dB. - Adjust METER CALlB ( fig. 6.6 -75 ) with trimpots CH 1 and CH 2, VU-meter indication 0 dB ( 100 % ).
-
If these noise and external voltage separations are not attained, the tape guide elements and magnetic heads are, once more, to be demagnetized carefully.
6.6.3.
-
Noise Voltage, External Voltage " Before-Tape " ( Check )
Switch recorder to STOP. Before-and-after-tape switch t o INP ( fig. 6.6 -78 ).
RECORD
Fig. 6.6-78
The noise and external voltage separation shall be more than 75 dB, referred to full-modulation.
Fig 6.6-75
Check of Input Amplifier :
- Set controls per fig. 6.6 -79
6.6.2.
-
Noise Voltage ( and External Voltage ) via Tape
-
Noise voltage measurements refer to full-modulation ( distortion factor 2 % at 7.5 ips, 3 % a t 3.75 ips resp. per 6.6.1. ) To avoid RF-interference errors, a tape erased on the recorder i s measured in the PLAYBACK mode.
- To avoid hum interference during this procedure, the microphone inputs ( jacks or cinch connectors are to be terminated with 200 ohm.
MONITOR
C" 1
CM,,
,N*",
n
CWAWNEL,
CMANnEL t,
RECORD
MONiTOR
@
RECORD
Fig. 6.6-76
@
Fig. 6.6-79
MAX
The noise and external voltage separations shall be more than 45 dB referred to full-modulation.
6.6.4.
Erase Attenuation
Following Measurements: Erase attenuation, crosstalk, mono and stereo ( 6.6.4 - 6.6.6. ) can be taken with a selective VTVNl ( band width less than 100 Hz ). To measure erase attenuation, a frequency of about 1000 Hz is recorded and consecutively erased. The record remaining on the tape is then measured. - Set controls per fig. 6.6 -80 - Record 1000 Hz, full-modulation.
Set playback function switch to CH 2, measure the crosstalk separation 1 - 2 and bring with crosstalk compensation trimmer ( fig. 6.6 -83 ) to best value ( more than 60 dB ).
Fig. 6 . 6 8 0
Fig. 6.6-83
-
STOP, rewind tape. Close record volume controls (fig. 6.6-81 ).
- Advance tape to recording on channel 2. - Set playback function switch to CH 1, measure crosstalk separation 2 - 1, correct P 305 i f necessary. For strong corrections, repeat crosstalk 1 - 2 measurement and adjust for mean value.
6.6.6.
Crosstalk,
Stereo
( selective 6.6.4. )
Measure and if necessary adjust mono crosstalk attenuation per 6.6.5. before checking the stereo crosstalk attenuation. Don't disturb P 305 compensation trimmer during the following measurements.
Fig. 6.6-81
-
-
The generator is switched in parallel on the AUX-inputs while measuring stereo crosstalk attenuation. Close the input to the channel to be measured. Set controls per fig. 6.6 -84.
- Switch recorder to Record and measure the erase attenuation. The remainders on the tape shall be better than 75 dB under the level of full-modulation.
RECORD
6.6.5.
Crosstalk, k'lono
( selective per 6.6.4. ) Fig. 6.6-84
----C
A mono-recording 1000 Hz full modulation is appropriately taken 1 min on CH 1 and afterwards 1 min on CH 2 for this measurement on a factory-tape. Note that the record butt on the unused channel is disengaged.
-
1-11
+11-
I
-
AF-generator 1000 Hz, full modulation, record stereo.
Set controls per fig. 6.6 -82. Measurement 1 - 2 :
-
AF frequency millivoltmeter at output CH 2, record volume control CH 1 fully open ( a t right limit ), record volume control CH 2 fully closed ( left limit ).
RECORD
MAX
Fig. 6.6-82
- AF frequency millivoltmeter at output CH 1, record volume control CH 2 fully open ( a t right limit ), record volume control CH 1 fully closed ( left limit ). - Crosstalk attenuation shall be better than 4 5 dB.
6.7.
Output Voltage Check
- Set controls per fig. 6.7 -85
Fig. 6.7-85
-
Load tape, switch to Record ( Stereo). AF-generator 500 Hz, full modulation. - AF frequency millivoltmeter a t output CH 1 or CH 2. Output voltage shall remain constant( 1 dB ),when the before-and-after-tape switch I NP / NAB / I EC and the playback mode switch STEREO / CH 1 / CH 2 / MONO i s switched around. If the output voltage doesn't stay within the indicated tolerance, proceed per 6.5.4.
-
*
6.8.
Wow
and Flutter
The values given in the technical data are measured with a wow and flutter meter per Std DIN 45507. Values obtained by a different standard can't be compared.
7.ACCESSORIES
7.1.
Remote Control
All push button functions can be accomplished by REMOTE CONTROL. The remote control cable needs no shielding and its length is not critical. The remote control unit circuitry is per fig. 7.1-86.
1
I
<
> >
PLAY
STOP
REC
1
REMOTE CONTROL PLUG
Fig. 7.1-86
( HIRSCHMANN WlST 10 )
The 27 Vdc on terminal 7 i s for use with slide projectors (load 150 mA maximum). The dummy connector must be inserted for operation without the REMOTE CONTROL unit (this dummy connector shorts terminals 1 & 2).
7.2.
Operation with a Timing Clock
The timing device is to be wired into the electric power feed in a manner which will provide electric current to the REVOX A77 during predetermined intervals only. For operation with a timing clock, the power switch and speed selector remains continuously in the position of the desired tape speed.
8. MODIFICATIONS
8.1. Rewind 8.6. Capstan Motor with Sleeve Bearings Modification effective from serial Nr. S 60483 and G 78003 for illustration see parkslist page E 10. The capstan shaft extends through the full length of the motor and is supported by two sintered-bronze bearings. The lower bearing is designed to restrict the axial movement of the shaft by means of a plastic coated thrust (low-friction) washer. All bearings are lubricated for their life and will normaly not require any service. Capstan shaft and low-friction washer may be replaced in the field. If a bronze bearing has become defective, the motor must be sent to the nearest factory service-center. (For disassembly instructions see section 3.7.)
For bad rewind with 18 cm ( 7" ) reels : Replace resistor R 125 ( 820 Ohm ) by resistor 1.2 kOhm, 9 Watt ( drive control 1.077.370 ).
8.2.
Switch Noise
The following change can improve the situation where operation of the STOP button out of RECORD and PLAY modes causes clicks : Ground connection brn ( fig. 3.13 -18 ) is unsoldered from the printed side and resoldered to the ground conductor at playback switch 55 ( switch board 1.077.435 1. Another improvement results from replacing the diode D 601 ( record relay card ) by an RC-network: C = 50 yF / 30 V, R = 100 Ohm / 118 W ( series connected, observe polarity ).
8.6.1. Removal of Capstan Shaft and low-friction Thrust Washer
8.3.
RFI
Removal of capstan shaft and low-friction washer is possible while the motor remains installed in the recorder.
-
Interference from strong radio an TV transmitters can be removed by the following measures : Solder 1500 - 5000 pF ceramic capacitors from ground connection shield ( shielded cable ) to chassis ( tubular rivet of connector fastening ) at the disturbed inputs ( see example C 154 OUTPUT terminal ).
Carefully remove shaft lock A b y pulling i t sideways with a pair of angled pliers. DANGER! Do no: attend to pry the lock loose with a screw-driver etc. because i t will fly off quite forcefully. Slide off the rotor portion of the capstan motor. After removal of the tape quide between the playback head and the capstan shaft, the shaft can be pulled up and out of the motor. (Take care not to disturb the setting of the adjusting nut on the tape quide.) To remove the low-friction washer take out the circlip B with the aid of special pliers. The bearing parts can now be disassembled in the following order: Springwasher E, low-friction washer F and thrust bearing G. The capstan shaft may now be removed by pulling i t downwards and out of the motor. When re-assembling the lower bearing, apply one dror, of lsoflex PDP65 oil to the low-friction washer.
Powerful UHF television transmitters may be picked up by the playback head cables. I f an interfering buzz occurs, the following change should be effected in the playback amplifier: Connect a capacitor of 100 pF (maximum 220 pF) from base to emitter of Q 803 (similar to C 803 on Q 801).
-
-
8.4. Transfer Play Sensitivity
Resistor R 316 and R 321 are 10 kOhm in recorders of lot 1. Substitution with 3.3 kOhm resistors ups recording sensitivity (gain 10 dB approx).
-
When handling shaft and bearing, extreme care must be exercised, so as to avoid damaging them and t o prevent any dust particles from entering the precision bearings. (runout accuracy 1/1000 mm).
8.5.
Replacement of Capstan Motor
Starting with Serial Nos. S15500 and G 16150 a new type of Capstan-Motor was installed which operates on a 20 V higher supply voltage and therefore requires a modified power-transformer. The voltage appearing at point E8 blu (speed control board 2.077.725) now measures 150 V. When using an old motor in conjunction with a new transformer, a type 40318 transistor must be used in position Q 209 on the speed control board.
9. TROUBLE SHOOTING
Pre - Check :
Check network voltage. Allowable deviation ( also for short periods ) at respective settings of the voltage selector :
110 Vac : 130 Vac : 150 Vac : 220 Vac : 240 Vac : 250 Vac :
rnin rnin rnin rnin min rnin
96 Vac, 112 Vac, 130 Vac, 190 Vac, 210 Vac, 225 Vac,
max max rnax max rnax max
125 145 165 245 270 290
Vac Vac Vac Vac Vac Vac
Use a regulator if the deviations are higher. Note that regulators have a marked leakage field ( keep far from recorder ). Check of regulated supply voltage 21 Vdc. Adjust on P 106 or replace diode D 104, if necessary.
9.1.
Faults in the Drive Check motor capacitor C 151. Check regulation electronics, test points ( diagram 1.077. 725 ). I f the capstan motor does not start by itself after manual stopping, the regulator preamplifier is oscillating. Exchange R 206 ( 100 Ohm) against 330 Ohm. Check capstan bearings, exchange ball bearings against factory - new original ones.
Capstan Motor fails t o run :
Capstan motor rumbles :
Exchange bearings against factory - new original ones.
Capstan motor whistles :
Check gap rotor t o pick-up ( per 6.2.1 ). Put a strip of rubber or equivalent between pick-up and its mounting surface for vibration isolation. Unpotted pick-ups are t o be exchanged f o r potted ones.
Tape Speed too low :
Check pick-up separation. Measure pick-up frequency ( per 6.2.2 ). Check regulation electronics, test points.
36
Wow and Flutter :
Mechanical causes : Periodic wow and flutter whose origin i s in a defective pressure roller or whipping capstan axis can be recognized by observing the rotating element's rythm ( pressure roller or capstan axis might be marked with felt tip pen ). Pressure roller, see also 4.4.1. If rythm of wow i s identical with the rotation of the lefthand reel motor, the origin may be either mechanical or electrical. The mechanical cause may be defective bearing or misadjusted brake.
Electrical causes : Overly strong counter torque of left-hand reel motor can be cause for wow; check motor voltages, see table 5.9 -46. If wow occurs only at 3.75 ips, it may have i t s origin in too large a distance of pick-up or in the regulation circuit,(see
6.2.1 1.
Wow at both speeds may be caused by a defective capacitor in the RC-network R 21 5 .C209 in the regulation circuit. 1 Replace capacitor.
Inadequate Starting Behavior, Slow Rewind :
1" Reels smaller than 60 mm ( 2 - 3 8 ) should not be used if at all possible.
Optimum behavior can be expected only at nominal line voltage. Check reel motors with loosened brakes for light run (axial 2" play of reel motors .2 to .3 mm ( .008to .0J ). Increase R 125 to 1 or 1.2 kOhm.
Push Buttons Don't Hold :
Dummy connector REMOTE CONTROL is missing. End-of-tape switch i s defectife, see 5.9.1, or strong light i s incident on photoresistor. Check relay operating voltage ( 27 Vdc ).
End-of-Tape Switch Doesn't Function :
Lamp defective. Check photoresistor and trigger, see 5.9.1.
37
Pressure Solenoid Doesn't Function :
Check drive control, relay contacts, and diode.
Brake Solenoid Doesn't Function :
Check solenoid coil. Clean core. Check relay operating voltage ( 27 Vdc ).
Brakes (STOP too weak, too strong, irregular :
Check brake bands, check brake lining. Clean and degrease. Measure brake tension per 4.3.
9 2 . Faults in Circuitry ..
Pre-Check :
See Pre-Check 9.
Playback Amplifier Hums :
Break in playback head windings. Flap shield doesn't close ade