Historical Document · 1953
The primary theory of operation: keyboard, RO base, typing unit (clutches, selector, code bars, type box positioning incl. Fig. 2-43, printing, spacing, functions), motors, cabinet, ESU; 60/75/100 wpm; 20/60 mA. 61 pp
Copyricur 1953 sy TELETY IN ALL COUNTRIES PARTICIPATING IN INTERNATIONAL AND PAN AMERICAN CONVENTIONS, ALL RIGHTS RESERVED INCLUDING RIGHTS OF TRANSLATIONS INTO ALL LANGUAGES, BULLETIN NO. 2168 TELETYPE PRINTING TELEGRAPH SYSTEMS BULLETIN NO. 216B GENERAL DESCRIPTION AND THEORY OF OPERATION MODEL 28 PRINTER Aaa. Ue MMT. OFF CORPORATION SUBSIDIARY OF Western Electric Company CHICAGO, US am [TELETYPE | PE CORPORATION tn UNITED STATES, Printed in U.S.A. 2168 LIST OF EFFECTIVE PAGES JUNE, 1953 PAGE CHANGE PAGE CHANGE NUMBERS IN EFFECT NUMBERS IN EFFECT A To C ORIGINAL l-1 TO 1-3 | ORIGINAL 2-0 TO 2-17} ORIGINAL 3-0 TO 355| ORIGINAL The above list indicates the effective pages as of the date of issue. When a change takes place in any of the following pages this page likewise changes. ORIGINAL Paragraph 216B TABLE OF CONTENTS SECTION 1 GENERAL DESCRIPTION 1. General, ........0.20.. 2. Description of Components. eso we a. Keyboard. ..... oe ewe b. Receiving-Only Base. ...... c. Typing Unit....4....4... d, Motor Units. ........ oe (1) Synchronous Motor Unit. ee (2) Governed Motor Unit. . oe e. Cabinet. ......... 0846 f. Electrical Service Unit. .. oe 3. Electrical Characteristics... . , SECTION 1. General. ........., ee ee 2. Signaling Code. ....... eo ee 3. Keyboard. ......... oe ee a. General. ..... «2 6 «© 2 © b. Intermediate Shaft Assembly, oe c. Code Bar Mechanism. ...... d. Signal Generator Mechanism... e. Local Carriage Return Mechanisn. f. Local Line Feed. ....., oe §- Break Mechanism ........ h, Repeat Mechanism. ....... i. Keyboard Lock Mechanism .... j. Keyboard Unlock Mechanism. .. . k. Margin Indicator Mechanism. . . 1. Time Delay Mechanism... . , . m, Repeat-On-Space Mechanism. ... 4. Receiving-Only Base. ....... ° 5. Typing Unit. ......0eee. . a. General, ......0-. sce eco b. Main Shaft. ......0.2.-eec6 c. Selecting Mechanism. ...... d. Orientation, ......... ° e. Printing Mechanism. ...... (1) Code Bar Mechanism .... (a) General. ....... (b) Code Bar Positioning . (c) Arrangement of Code Bars (2) Type Box and Type Box Carriage. , (a) General... 2.0.4, (b) Positioning. toes . oo (3) Printing Hammer and Printing Carriage (a) General. ........ (b) Positioning. ... . (c) Printing. ...... f. Spacing. ......0.+.s.e6. . (1) General. .... so (2) Spacing Suppression oe eo ORIGINAL ° * o 8 © Page 1-1 1-1 1-1 1-2 1-2 1~2 1-2 1-2 2-0 2-0 2-0 2+0 2-0 2~1 2-2 2-2 2-2 2-2 2-2 2-3 2-3 2-3 2-3 2-4 9A an 2-4 2-4 2-5 2-5 2-5 2-5 2-5 2-6 2-6 2-6 2-7 2-8 2-8 2-8 2-8 2-9 2-9 2-9 Paragraph g. Margin Indicator . . «6. «4. +» h. Ribbon Mechanism. ..... . ° . se ee (1) Positioning . . «6 «2 © es © © » os oo (2) Feeding... 6 2 so ee we eee oo 6 i. Functions. .... 2 «+ +2 © © © © © © oe oe * (1) General... 46 + © © oo + we we © oo ew (2) Letters and Figures Shift Function. eee (3) Spacing Function. ... 2» ++ «+s oe ewe (a) Spacing. . .. oo ++ ee es soe ee (b) Unshift on Space. .... - oe ee o (4) Carriage Return Function. . «+ « « cee oe (5) Line Feed Function. . ... + +e ee cee (6) Automatic Carriage Return - Line Feed Function. (7) Signal Bell Function. ... ++ «+ 2 0 (8) Blank Function. . »- . + +o ++ oe» eee ee (9) Motor Stop Function. ...+-++ + oe eo ee Motor Units. . . 2. oo « « «© «© © © © © © # © e+ oe a. Synchronous Motor Unit... +++e«-++ > oe ow b. Governed Motor Unit. . . - «6 «© + + © @ « oe oe Cabinet and Electrical Service Unit. ... - os ee a. General. . 1... 0 + e+ s+ © ee @ © © 22 8 coco ee b. Basic Electrical Service Unit. . .- +. -s oo oo c. Electrical Motor Control Mechanism... eo eo ee (1) Stop Position. ...+..+s-++eee-e oe we (2) Open Line Position, . . . « « «© © « oe oe (3) Start Position. ....-++« +s -s owe oe (4) Stop Position... ++so-+-+8e-s eo eco SECTION 3 FIGURES FOR SECTIONS 1 AND Page - 2-9 . 2-9 . 2-9 2 2-10 . 2-10 . 2-10 ° 2-11 2 2@-ll . 2-11 . 2-12 . 2-12 ~ 2-12 . 2-13 . 2-13 » 2-13 . 2-14 . 2-14 . 2-14 » 2-15 . 2-15 . 2-16 . 2-16 2 2-17 . 2-17 ~ 6 217 ORIGINAL 216B SECTION 1 GENERAL DESCRIPTION 1. GENERAL a. The Model 28 Printer described herein is used to exchange typewritten page messages be- tween two or more distant points when connected by a_ telegraph channel. The operating speeds are in the order of 368 opm (60 wpm), 460 opm (75 wpm), and 600 opm (100 wpm) as desired. Sets of gears for the various speeds are sup-~ plied as optional components. Signaling be- tween Stations is accomplished electrically by use of the five-unit start-stop permutation code. b. The equipment is wired at the factory for operation on 0.060 ampere signal line current but, by making a convenient wiring change in the Electrical Service Unit and readjusting the selector armature spring, it may be adapted for operation on 0.020 ampere signal line current. c. Messages are ordinarily typed on single- copy paper eight and one-half inches wide. However, multiple copy paper or paper of lesser varying widths (minimum three inches) may be used. 2. DESCRIPTION OF COMPONENTS a. KEYBOARD. (See figure 1-2.)~ The Key- board supports the Motor Unit and the Typing Unit and incorporates code selecting and signal generating mechanisms, Signal line and power line circuits are also included. A time delay mechanism which (when used in conjunction with a motor control mechanism in the Electrical Service Unit) will stop the Motor on extended idle periods of the signal line may be supplied as an optional feature. The keys are positioned in the conventional three-bank arrangement with numerals, punctuation marks, and special sym- bois available in upper case positions (figure 1-2). Special keys for line break, keyboard lock and unlock, repeat operation, and local carriage return and line feed are located di- rectly above the lower three rows of standard keys for facility of operation. A repeat~on- space mechanism is included when required. The Keyboard with the Typing Unit and Motor Unit mounted in position is placed upon a cradle within the Cabinet. The front of the Keyboard protrudes beyond the Cabinet and is fitted with a rubber pad that seals the edges of the aper- ture for a silencing effect. Motive force for activating the Keyboard is derived from the Motor by way of the Typing Unit. b. RECEIVING-ONLY BASE. (See Figure 1-3.) - The Receiving-Only Base is used in place of the Keyboard when receiving facilities only are re- quired. It supports the Motor Unit and the ORIGINAL Typing Unit and provides for local carriage re~ turn and local line feed operation of the Typ- ing Unit. It does not incorporate code select- ing and signal generating mechanisms. A time delay mechanism may be included if required. c. TYPING UNIT. (See figures 1-4 and 1~5.) (1) The Typing Unit incorporates’ the necessary electrical and mechanical features for translating the code signals into mechan- ical action in order to record the message and nerform the usual functions incident thereto. (2) Code signals are applied to a_ two- coil magnet associated with a selecting mechan-~- ism which interprets the signals and controls the motions involved in typing a character or performing a required function. Means are pro- vided for orienting the selector to the re- ceived signal. The Motor is geared to the main shaft of the Typing Unit which, in turn, ex- tends motion to the keyboard mechanism. The typing and various functional sections of the Typing Unit are activated by individual clutches that completely disengage at the term- ination of each operating cycle and thus reduce the motor load to the minimum when idling. (3) For friction feeding, the paper feeds from a five inch diameter roll mounted on the Typing Unit and passes around a_ stationary platen. However, the Typing Unit may be equipped with a sprocket feed mechanism to ac- commodate fan-fold forms. Paper spindle latches may be provided as an optional feature. Interchanging of Typing Unit sub-assemblies in- volves the minimum in readjusting procedure (figures 1-6, 1-7 and 1-8). Type pallets are arranged in a compact, lightweight type box which may be readily detached for cleaning or for replacement by another type box. In opera- tion, the type box keeps step with a printing carriage and presents the proper type pallets to the printing hammer to receive its strokes as the printing carriage advances along the line. Combined automatic carriage return and line feed functions operate to return the carriages and advance the paper to prevent overprinting at the end of a line should the carriage return combination not be received in time, Motor stop contacis may be provided as an optional feature. (4) In addition to the conventional functions common to printing telegraph equip- ment, built-in facilities permit the addition of selective station call or recognition func- tions with electrical circuits associated therewith available for remote extension. In such applications the Typing Unit may be 1-3 stripped of all typing and paper feeding mech- anisms and utilized for circuit switching or Similar applications. (5) The type box and function box are features that will vary with the type and func- tion arrangements desired. d. MOTOR UNITS. - The Motor Units are self- contained components that mount on the rear of the Keyboard or Receiving-Only Base and have characteristics adaptable to standard power supplies. (1) SYNCHRONOUS MOTOR UNIT. 1-9.) (See figure (a) The Synchronous Motor Unit con- tains a wound stator, two pole, single phase, capacitor start, motor. A combination hand- wheel and fan is mounted on one end of the motor shaft. A motor-starting relay and ca- pacitor, together with a thermal cutout switch, are mounted in a compartment on the underside of the Motor Unit. The thermal cutout switch (manually reset) serves to protect the motor windings from excessive heating. (b) The motor proper is supported by a cradle to which it is held by straps at each end. Resilient mounts on the hubs of the motor end bells reduce transmission of vibration to the Keyboard or Receiving-Only Base. (2) GOVERNED MOTOR 1-10.) UNIT. (See figure (a) The governed motor is series wound and is similar to the synchronous motor in its mounting arrangement. (b) A combined governor and fan are positioned on the motor shaft extension, The fan draws cooling air through the motor as an aid in controlling the temperature rise. A target for speed-checking purposes is painted on the governor cover. The cover also serves to protect the governor mechanism. A screw- driver opening is provided in the cover to fa- cilitate speed adjustment. Brush filter capacitors are provided within the motor end bells. A compartment on the underside of the motor unit houses the governor resistor and capacitor, as well as a power leads electrical noise suppressor, e. CABINET. (See figure 1-1.) cabinet is of sheet metal construction and is finished internally and externally in baked enamel, It is approx~ imately 40 inches high, 203 inches wide, and 183 inches deep. The upper portion forms a compartment for housing the mechanical units and the Electrical Service Unit. A shelf (1) GENERAL. The 1-2 216B located in the lower section may be used to support a Rectifier (not furnished as part of the Model 28 Printer). The top of the Cabinet the rear. The push button and is a mechanism that aids in raising it and then supports it in the open position. A copyholder is attached to the front of the dome. A window through which the message may be read while being printed is located in the upper portion of the dome. This window is in a nearly horizontal position to avoid reflection from ceiling lights. A hinged door in the dome is unlatched by a push button to permit access to the printed copy. The copy is illuminated by a copy light located under the dome. Rubber sealing strips are applied to the edges of both the dome and the door for Silencing purposes. A rubber mounted cradle includes a tilting arrangement which permits the assembled Keyboard, Motor, and Typing Units to be tilted forward and supported when the dome is open (figure 1-11). This provides maximum accessibility to the mechanism while servicing. Terminal boards for power and sig- nal line connections are located on the inner rear wall (figure 1-12). The Electrical Service Unit is located to the rear of the Key- board. Its power switch is controllable from a switch lever at the front of the Cabinet. The Cabinet may be equipped with the following features to meet the customers requirements. forms a dome that is hinged at dome is unlatched by a counterbalanced by (a) <A signal bell. (b) A margin indicator lamp. (c) Two electrical noise which minimize electromagnetic the power and signal lines Cabinet. suppressors radiation from | external to the (d) A combination lower compartment cover panel and maintenance plate. This panel, which normally is snapped in place in front of the rectifier shelf in the lower portion of the Cabinet, may be installed horizontally in the upper part of the Cabinet with its inside surface facing upward. In this position the panel serves as a work shelf upon which the Typing Unit may be placed for servicing. f. ELECTRICAL SERVICE UNIT. (See figure 1-13.) - The Electrical Service Unit is located in the upper compartment of the Cabinet. It incorporates receptacles, fuses, switches, etc., which are associated with the power and signal line circuits. The unit may include any of the following optional features: (1) Motor control mechanism. (2) Signal line relay mounting assembly. (3) 0.100 ampere rectifier assembly. ORIGINAL 216B (4) Current limiting resistors for oper- (b) Phase: Single phase. ation of the Model 28 Printer on DC. (c) Frequency: 60 cycles $0.75 per (5) Line test key assembly. cent. 3. ELECTRICAL CHARACTERISTICS. (d) Input current: a. The SIGNALING FREQUENCY of the output Starting. ....... . .9 amps. telegraph signal is expressed in maximum dot cycles (one cycle is one current impulse fol- Running ....... . 1.85 amps. lowed by one no-current impulse) per second: (e} Power Factor. .... . 0.30 Speed Frequency (f) Wattage ........ . 65 watts 60 words per minute - 22.8 cycles (g) Heat Dissipation. . .. . 50 watts 75 words per minute - 28.5 cycles 100 words per minute ~ 37.1 cycles (2) GOVERNED MOTOR UNIT. — This data for Governed Motor Unit used without current limit- b. The selector magnet responds to marking ing resistors in Electrical Service Unit. and spacing start-stop signals and may be con- nected for either 0.020 ampere or 0.060 ampere line current. (a) Input voltage: 115 volts = 10 per cent a-c. Note (b) Phase: Single phase. The rectifier, when incorporated in the Electrical Service Unit, has sufficient (c) Frequency: 50 to 60 cycles. output (0.100 ampere, 115 VDC) to supply the selector magnet and the relay bias (d) Input current: winding circuits. However,this rectifier does not have sufficient output to also Starting. ..... . . 1.75 amps. supply the signal line current. Running . .....se-. 1 amp. c. POWER SUPPLY REQUIREMENTS. (e) Power Factor. .... . 0.83 (1) SYNCHRONOUS MOTOR UNIT. (f) Wattage... ...2e 95 watts (a) Input voltage: 115 volts + 10 per cent a-c. (g) Heat Dissipation. ... 75 watts ORIGINAL 1-3 216B SECTION 2 THEORY OF OPERATION 1. GENERAL. a. This section covers the operating prin- Ciples and circuit descriptions of the Model 28 Printer. This equipment serves as a sending and receiving (or receiving only) page-type printing telegraph set when connected to the terminal facilities of a wire or radio tele- graph circuit, and will operate on signal line current of either 20 or 60 milliamperes without a line relay. The signals received by the Model 28 Printer are of the start-stop type. The equipment is wired at the factory to trans- mit neutral signals but is readily adaptable to transmit polar signals by wiring changes. The equipment is designed to operate at speeds of 368, 460, or 600 operations per minute (opm). Conversion from one speed to another is made by changing gears. Synchronous Motors require a power supply of 115 volts (plus or minus 10 per cent) 60 cycle, single phase alternating cur- rent. To avoid loss in receiving margin with this type of motor, the frequency regulation must be within plus or minus 0.75 per cent. Governed motors require a like power supply ex- cept that the frequency may be from 50 to 60 cycles. b. The electrical and mechanical relation- ships of the units which make up the Model 28 Printer, when equipped with a motor control mechanism as an accessory, are shown in a func- tional block diagram (figure 2-1). 2. SIGNALING CODE. The signaling code is a five unit start-stop code of current and no-current intervals. In- tervals during which the selector magnet is en- ergized are known as marking impulses, and those during which the magnet is not energized are known as spacing intervals. Each group of five selecting intervals is preceded by a start interval (no-current) and is followed by a stop impulse (current) both of which are used to maintain synchronism between the transmitting and receiving apparatus. Figure 2-2 shows, graphically, the code used. 3. KEYBOARD. a. GENERAL. ~ The Keyboard embodies a sheet metal structure on which an intermediate shaft assembly, a code bar mechanism with keylevers, and a signal generator mechanism are mounted. It also contains a margin indicator switch mechanism, and provides mounting facilities for a Typing Unit and a Motor Unit. At the time a Keyboard is installed in its Cabinet, a plug on the end of a plastic covered cable that extends from the left end of the Electrical Service 2-0 Unit (figure 1-13), is plugged into a connector mounted on the top left rear corner of the Key- board (figures 1-2 and 1-11). See figure 2-3 for schematic wiring. In operation, the motor drives the intermediate shaft assembly which furnishes motive force to the typing unit main shaft (figures 1-5 and 1-7). This, in turn, drives the signal generator helical driven gear which is connected to the keyboard clutch drum by a sleeve. Thus, the keyboard clutch drum is caused to rotate continually while the motor is running. The transmitting cam-clutch assembly of the signal generator mechanism remains sta- tionary except when motion is extended to it from the keyboard clutch drun, Engagement of the clutch is brought about by the operation of any key in the lower three rows, or the space bar,and a transmitting cycle 1s then initiated. b. INTERMEDIATE SHAFT ASSEMBLY. - The inter- mediate shaft assembly, located in the rear central portion of the Keyboard (figure 1-2), supports two helical gears (one with an over- load clutch) and an eccentric cam. When the Motor Unit and the Typing Unit are in place on the Keyboard, the intermediate shaft helical driving gear on the motor engages with and drives the intermediate helical driven gear and its attached intermediate shaft assembly. This Shaft assembly includes the overload clutch and helical gear assembly which transfers the motive force to the typing unit main shaft, and when required, the eccentric bushing which drives the eccentric follower pawl on the time delay mechanism accessory. The gear ratio be- tween the intermediate shaft helical driving gear on the motor, and the helical driven gear on the intermediate shaft, determines the max- imum speed (operations per minute) at which the equipment will operate. These gears are read- ily replaceable with gears which will furnish other operating speeds. The overload clutch lever disengages its notch in the main. shaft helical driving gear if the Typing Unit or the Keyboard become jammed. This removes all driv- ing torque from these units to prevent damage to the equipment. The clacking sound made by the overload clutch lever as it strikes its notch with each revolution of the intermediate shaft serves as an audible alarm. To re-engage the overload clutch, the power must be removed from the Motor Unit and the motor must be turned over by hand until the overload clutch lever falls into its notch. If the trouble in the equipment is not cleared before the Motor Unit is re-energized, the clutch will immedi-~ ately disengage again. c. CODE BAR MECHANISM. - The code bar mech- anism is located in the front underside portion of the Keyboard. Each keylever in the lower ORIGINAL three rows and the space bar is connected to a code lever and each keylever in the upper row is connected to a function lever. The code and function levers pivot about points near their midportions (figure 2~4), Located above the rear half of the code levers and running par- allel with the front of the Keyboard are, from rear to front, the clutch trip bar, the upstop bar, the numbers 1, 2, 3, 4, and 5 code bars, and the lock bar. The rear portion of each code or function lever normally is held down- ward by a spring so that the front end, with its attached keylever, is held upward, A lock- ing wedge is mounted on the projection of the lower front portion of all code levers, the local line feed function lever, and the local carriage return function lever (figures 2-4 and 2-5). If one of these levers is operated, its locking wedge moves downward between the lock balls in the lock ball channel, and crowds them together. This prevents any other lever with a locking wedge from being operated at the same time, With the keyboard shaft in its stop position, the clutch trip bar and the five code bars are held toward the left (front view), against the tension of their springs, by the latched-up code bar bail. When any keylever in the three lower rows or the space bar is de- pressed, the rear end of the associated code lever engages and lifts the front edge of the code lever bail (figure 2-6). An extension on the code lever bail disengages the code lever bail latch lever and permits it to drop. As the front edge of the code lever bail rises, the back edge rotates around the rear end of the operated code lever and locks it in posi- tion. As the code lever bail latch lever drops, it depresses the code bar bail latch lever and releases the code bar bail (figure 2-7). Upon being freed, the code bar bail, the clutch trip bar, and the five code bars are pulled toward the right by their springs, until the code bar bail strikes its bumper. As the five code bars shift, code projections on un- selected code bars engage the operated code lever (figure 2-8). Code bars which are per- mitted to move to the extreme right become selected and carry with them their respective transfer levers. By means of the clutch trip bail and the clutch stop lever, the clutch trip bar releases the keyboard cam-clutch which ro- tates on the shaft. During the time in which the cam-clutch makes a revolution, an eccentric cam and its follower cause the code bar bail, the five code bars, and the clutch trip bar to be returned to their original positions (fig- ures 2-9 and 2-10). As the code bar bail moves to the left, it carries with it the non-repeat lever (figure 2-11). This in turn rotates the non-repeat bell crank about its pivot point until it lifts the code lever bail latch lever out of engagement with the code lever bail ex- tension, While a spring then returns the code lever bail to its normal position, the code lever bail extension drops on the non-repeat lever to disengage it from the code bar bail. ORIGINAL 216B The spring then resets the non-repeat mechanism, As the code lever bail returns to its normal position, it releases the operated code lever and its keylever. As the cam-clutch nears the end of its revolution, the clutch shoe lever strikes the stop lever, and the inertia of the cam disk assembly causes it to continue to turn until its lug makes contact with the lug on the clutch shoe lever. At this point the latch lever drops into the indent in the cam disk and the clutch is held disengaged until the stop lever is again operated (figure 2-12). For de- tailed information on the operation of the clutch shoes, see paragraph 5.b.(3) of this section. d. SIGNAL GENERATOR MECHANISM. - The Signal generator mechanism is located on the top front part of the keyboard base. As was shown in paragraph 3.c., each of the five code bars op- erates its own transfer lever (figure 2-13). In addition to these five transfer levers, there are two others which are not associated with code bars and which are used to originate the start and stop pulses. The stop pulse transfer lever (seventh from the rear and located next to the fifth pulse transfer lever) is permanently positioned so that its upper end, and its associated selector lever are toward the left or selected position, The start pulse transfer lever (third from rear and located between the second and third pulse transfer levers) is permanently positioned so that its upper end, and its associated selector lever are to the right or unselected position, When a code bar is unselected, the upper end of its transfer lever and its associated selector lever are positioned toward the right (figure 2-13). When a code bar is selected, the upper end of its transfer lever and its associated selector lever are positioned toward the left (figure 2-14). After the code bars have posi- tioned their transfer levers and selector lev- ers, the locking bail which is operated by a cam on the keyboard cam-clutch assembly drops downward between the lock projections on the upper ends of the transfer levers (figure 2-15). When the selected code bars are reset by the code bar bail, the upper end of their transfer levers are held toward the left by the locking bail. The slotted bearings at their pivot points permit the transfer levers to shift to the left without disturbing the selection set up on the selector levers. Each of the seven selector levers is associated with a cam on the cam-clutch assembly. These cams push the levers upward briefly in the order: start, 1, 2, 3, 4, 5, and stop. A rocker bail is located above the selector levers and is actuated by them. A rocker bail detent holds the bail in either of the two positions it can assume. When a se- lector lever which is in the unselected position (toward the right) is pushed upward by its cam, it rotates the rocker bail clockwise (fig- ure 2-13). When a selector lever which is in the selected position (toward the left) is 2-1 216B pushed upward by its cam, it rotates the rocker bail counterclockwise (figure 2-15), An ex- tension on the rocker bail is moved downward or upward respectively with clockwise or counter~ clockwise rotation of the bail. On the rear Side of the signal generator mechanism are 1lo- cated the upper or spacing intermediate lever, the lower or marking intermediate lever, the oscillating lever, the flutter lever, the de- tent toggle, and the detent lever. In the stop position, the rocker extension holds the mark- ing intermediate lever downward and out of en- gagement with the flutter lever (figure 2-16). As the flutter cam on the keyboard cam-clutch assembly rotates, it moves the flutter lever and the spacing intermediate lever toward the left as viewed from the rear (figure 2-17). The spacing intermediate lever bears on the upper part of the oscillating lever and rotates it counterclockwise so that the detent toggle is shifted toward the left where it is held by the detent lever. The detent toggle moves the toggle extension in the contact assembly (on the top side of the signal generator mechan- ism), toward the left and causes the contact toggle to pivot on the spacing contact and break the marking contact (figure 2~18). This breaks the line circuit which passes through the contact toggle and the marking contact and originates a start or spacing interval of the Signaling code. When the rocker extension is in its upward position, it holds the spacing intermediate lever upward out of engagement with the flutter lever and the marking inter- mediate lever toward the left. The marking intermediate lever bears on the lower part of the oscillating lever and rotates it clockwise so that the detent toggle is shifted to the right where again it is held by the detent lever. The detent toggle moves the toggle ex~ tension in the contact assembly toward the right and causes the contact toggle to close with the marking contact and pivot on it (fig- ure 2-20). This closes the line circuit and originates a marking impulse of the signaling code. The electrical noise suppressor is in the line circuit to aid in the suppression of undesirable radiation when the circuit is broken. e. LOCAL CARRIAGE RETURN MECHANISM. - Opera- tion of the local carriage return keylever causes its function lever to raise the forward end of the local carriage return bail (figure 2-21). The bail rotates about its pivot point until the upper end engages the carriage return lever on the Typing Unit. Thus, the carriage return mechanism on the local Typing Unit is made to operate without disturbing the other Typing Units on the same line circuit, The carriage return mechanism is fully described in paragraph 5.i. (4) of this section. f. LOCAL LINE FEED. - Operation of the local line feed keylever causes its function lever to 2-2 raise the forward end of the local line feed bail (figure 2-22). The bail rotates about its pivot point and the upper end pushes the trip link until the link engages the line feed clutch trip lever on the Typing Unit. Thus, the line feed mechanism on the local Typing Unit is made to operate without disturbing the other Typing Units on the same line circuit. The line feed mechanism is fully described in paragraph 5.i. (5) of this section. g. BREAK MECHANISM. ~ Operation of the break keylever causes its function lever to raise the break rod and shift the break bail (figure 2-23). As the break bail moves upward, its lower end engages the lower end of the oscil- lating lever to rotate the lever counterclock- wise as viewed from the rear (figure 2-24). The oscillating lever shifts the detent toggle toward the left where it is held by the detent lever. The detent toggle moves the toggle ex- tension in the contact assembly toward the left and causes the contact toggle to pivot on the spacing contact and break the marking contact (figure 2-18). This breaks the line circuit until the break keylever is released. When the keylever is released, a spring on the break bail moves it downward. The upper end of the bail engages the upper end of the oscillating lever to rotate it clockwise and close the marking contacts in the contact assembly. h, REPEAT MECHANISM. - Operation of the re- peat keylever simultaneously with one of the keylevers in the three lower rows or the space bar disables the non-repeat mechanism and causes the character or function selected to be repeated as long as the repeat keylever is held operated. The operated repeat keylever causes its function lever to raise the right end of the non-repeat lever (figures 2-11 and 2-25), and rotate it about its pivot point. In this position, the non~repeat keylever cannot be en- gaged and operated by the code bar bail. Therefore, the non-repeat bell crank will not reset the operated code lever bail latch lever which then maintains both the code lever bail and the code bar bail latch lever in their operated positions until the repeat keylever is released, i. KEYBOARD LOCK MECHANISM. - Operation of the keyboard lock keylever causes its function lever to raise the keyboard lock bar pawl (fig- ure 2-26). As described in paragraph 5.i. (8) of this section, the reception of two consecu- tive blank code signals by the Typing Unit re- sults in its driving its keyboard lock lever downward, The lock lever makes contact with the lock plunger on the Keyboard and also pushes it downward. As the plunger moves, it exerts pressure on the yield spring which con- nects it with the keyboard lock bail. The bail rotates about its pivot point to engage the Keyboard lock function lever and causes. the ORIGINAL lever to raise the lock bar pawl. Thus, the pawl may be raised either by local operation of the keyboard lock keylever, or by operation of the blank or break keylevers, on any Keyboard in the line circuit. In its upper position, the pawl releases the keyboard lock bar and a spring pulls the bar toward the right (figure 2-28). In this position, projections on the lower side of the bar block the upward move~ ment of any code lever and the repeat function lever. j. KEYBOARD UNLOCK MECHANISM. ~ Operation of the keyboard unlock keylever causes its func- tion lever to rise against a camming surface on the keyboard lock bar and drive the bar toward the left until the lock bar pawl drops into a notch in the lock bar (figures 2-27 and 2-28). In this position, the projections on the lock bar lie between the code levers and offer no interference with their operation. k. MARGIN INDICATOR MECHANISM. - The margin indicator cam disk on the typing unit spring drum rotates with the drum as printing or spac- ing occurs. See paragraph 5.g. (1) of this section. As the end of each line is approached, the cam surface of the disk makes contact with the margin indicator contact lever and rotates it clockwise about its pivot point (figure 2-29). When the contact lever leaves’ the switch plunger, the margin indicator switch op- erates and closes the circuit to a margin in- dicator light in the Cabinet (figures 2-3 and 2-79). A carriage return cycle returns the cam disk to its starting position and the margin indicator switch opens. 1. TIME DELAY MECHANISM - As shown in para~ graph 7.c. of this section if an electrical motor control mechanism is furnished with the Electrical Service Unit, it must receive an electrical pulse to stop the motor. Such a pulse may be supplied by a time delay mechan-~ ism on the Keyboard. This mechanism contains two ratchet wheels - one with 27 teeth, and one with 28 teeth, A reciprocating eccentric fol- lower pawl, powered by the intermediate shaft, drives the ratchet wheels one tooth at a time (figure 2-30). Therefore, the ratchet wheel with 27 teeth turns a little faster than the one with 28 teeth. The latch pawl rides the inside flanges of the ratchet wheels. The con- tact pawl is held away from the flanges by the contact pawl latching lever which is controlled by the latch pawl. Each ratchet wheel has an identation in its inside flange. After a max- imum of 756 revolutions of the intermediate shaft, these indentations are adjacent for nearly one revolution. When the adjacent in- dentations pass over the latch pawl, it drops into them briefly and disengages the contact pawl latching lever from the contact pawl. ORIGINAL 216B This allows the contact pawl to ride the flanges of the ratchet wheels until either one of two things occur (figure 2~31). If a line signal is received before 756 revolutions of the intermediate shaft have taken place, the main bail drive bracket extension on the Typing Unit engages the upper end of the contact pawl and causes it to again be latched by the con- tact pawl latching lever. If a line signal is not received before 756 revolutions of the intermediate shaft occur, the identations in the flanges of the ratchet wheels again become adjacent so as to permit the contact pawl to drop into them briefly and pulse the motor stop switch (figure 2-32), This pulse is applied to the electrical motor control mechanism in the Electrical Service Unit to shut down the motor. The time lapse between the reception of the last line signal and the stopping of the motor varies from 86 to 172 seconds for 60 words per minute operation, and from 53 to 106 seconds for 100 words per minute operation, If it is not desirable to have the motor shut down auto- matically, the time delay mechanism may be dis- abled. To accomplish this, loosen the nut on the pilot screw, raise it to the top of its slot, and tighten the nut. When the pilot screw is in this position, the eccentric fol- lower pawl is held out of engagement with the ratchet wheels. m. REPEAT-ON-SPACE MECHANISM. ~ When a Key~- board is equipped with a repeat-on-space mech- anism (dashed outline, figures 2-7 and 2-9), it will automatically transmit the space function as long as the space bar is held operated. When the space bar is depressed, the rear por- tion of the space code lever engages and lifts the lower end of the space repeat lever. As the space repeat lever turns clockwise (viewed from front of Keyboard) its frontward projec- tion engages the lower projection on the code bar bail latch lever. Thus, the code bar bail latch lever is made to drop downward (figure 2-7) in which position it is held until the space bar is released. 4, RECEIVING-ONLY BASE. (See figure 1-3.) The Receiving-Only Base is a sheet metal structure which supports an intermediate shaft assembly (paragraph 3.b.) and provides mounting facilities for a Typing Unit and a Motor Unit. On the front of the base two off-line function keylevers, local carriage return and local line feed (paragraphs 3.e. and 3.f.), are mounted. At the time a Receiving-Only Base is installed in its Cabinet, a plug on the end of a plastic covered cable that extends from the left end of the Electrical Service Unit (figure 1-13) is plugged into a connector mounted on the top left rear corner of the Receiving-Only Base. 2-3 216B 3. TYPING UNIT. a. GENERAL. (1) The receiving circuit of the Typing Unit (figure 2-33) consists of two 132 ohm selector magnet coils wired to a connector which is mounted on the typing unit right frame (figure 1-4). At the time the Typing Unit is installed in its Cabinet, a plug on the end of a plastic covered cable that extends from the right end of the Electrical Service Unit (fig- ure 1-13) is plugged into this connector. A selector magnet terminal board in the Electric- al Service Unit provides for the connection of the selector magnet coils in series for 0.020 ampere line current operation, or in parallel for 0.060 ampere line current operation. (2) The Typing Unit also has a set of electrical contacts which are wired to the con- nector on its right frame. These contacts are used to pulse a signal bell when it is in- stalled in the Cabinet and are operated by a mechanism described in paragraph 5.i.(7). b. MAIN SHAFT. (See figure 2-34.) (1) The main shaft is located in the lower rear portion of the Typing Unit and ex- tends the full length of the unit. It is sup- ported by ball type bearings mounted in each side frame. (2) At the time the Typing Unit is mounted on a Keyboard, the keyboard helical driving gear on its main shaft meshes with the Signal generator helical driven gear. The main shaft helical driven gear meshes with the main shaft helical driving gear on the motor driven intermediate shaft on the Keyboard. Thus, motive force is extended from the motor to the main shaft which in turn drives the keyboard mechanism. (3) The main shaft includes six clutches each of which, when tripped, drives its as- sociated mechanism. These clutches have two shoes which bear against the inside surface of a drum which, in turn, is keyed to the main shaft. They operate as follows: (a) Figure 2-35 shows a clutch dis- engaged, Disengagement is accomplished by bringing together lug A on the clutch cam disk, and the lower end of clutch shoe lever B. The upper end of lever B pivots about its ear C and allows its other ear D to move toward theright. The upper spring then pulls the two shoes. to- gether and away from the drum, (b) Figure 2-36 shows the same clutch engaged. This is accomplished by re- leasing lug A and the lower end of lever B. The upper end of lever B pivots about its ear C 27-4 (which bears against the upper end of the sec- ondary shoe) and moves its ear D, and the upper end of the primary shoe, toward the left until the shoe makes contact with the drum at point gE. As the drum turns counterclockwise, it drives the primary shoe downward so that it again makes contact with the drum, this time at point F. There, the combined forc