Bell 501-165-117 Service Manual

BELLSYSTEMPRACTICES SECTION 501- 165-117
AT&_ Standard Issue2, September 1982

72-TYPE STATION DIALS

IDENTIFICATION, CONNECTIONS, AND MAINTENANCE

1. GENERAL

1.01 This section contains information on the f

72C3A manufacture discontinued (MD),

72D3A (MD), and 72E3A (MD), 72H3A, 72J3A, and
72K3A dials (Fig. 1, 2, 3, and 4).

i.02 The reasons for reissuing this section are

listed below. Revision arrows are used to em-

phasize the more significant changes.

• Add information on 72H3A, 72J3A, and
72K3A dials

• Show 72C3A, 72D3A, and 72E3A dials MD.

1.03 The 72C3A (MD) dial replaces the 35A3A, t

35Y3A, and 35Y3D dials used in 2500- and "

2554-type telephone sets. The 72D3A (MD) dial re .... ,_

places the 35AH3D dial used in some DESIGN LINE*
decorator telephones. The 72E3A (MD) dial replaces

the 35BB3D dial used in TELSTAR* telephone (DE- Fig. 1--1_72C3A (MD) Dial, Front View4
SIGN LINE decorator telephone).

/

1.04 SThe 72H3A, 72J3A, and 72K3A dials replace

a 72-type dial, determine if a polar- (MD) dials, respectively. These dials are similar ex-

ity guard has been installed in con- cept for the mounting brackets, switch plate, and
Before replacing a 35-type dial with the 72C3A (MD), 72D3A (MD), and 72E3A

junction with the 35-type dial. printed circuit board materials used in

Where no polarity guard exists, re- manufactureAI

move the 3g-type dial and refer to

Table A for 72-type dial connections
and handset cord jack lead connec- A. Purpose

tions. If a polarity guard exists, it

must be removed and the telephone 2.01 The 72-type dial is an electronically switched

set wiring arranged to agree with 12-button TOUCH-TONEr telephone dial. Ten
the factory wiring before a polarity of the pushbuttons are used for number or number
guard was installed. Refer to appro- and letter calling and two pushbuttons designated *

priate telephone set connection sec- and # are for special services.

tion in Division 502 for 2500- and
2554-type telephone sets and Divi- B. Ordering Guide

sion 503 for DESIGN LINE decora-
tor telephone. 2.02 Order dial as follows:

•Registered Trademark of American Telephone and Telegraph
Company.

Not for use or disclosure outside the

Bell System except under written agreement

Printed in U.S.A. Page 1

2. IDENTIFICATION

_.Trademark of American Telephoneand Telegraph Company.

NOTICE

SECTION501- 165-117

TERM NAL D .],:I

• -_ f ,/ .......'

TERMINAL

Fig. 4--$72H3A Dial, Rear View41

Fig. 2--072C3A (MD) Dial, Rear View(I • Dial, $72H3A0 (buttons and coverplate are

gray, button graphics are white)

• Dial, $72J3A¢ (buttons and coverplate are

.........

white, button graphics are black)

• Dial, $72K3AII (buttons and coverplate are

black, button graphics are white).

C. Design Features

2.03 Each of the pushbuttons, when operated, gen-
erates a dual tone multifrequency signal dis-

......................................................... frequencies for each button. Both the signaling and

tinctive to that button. Figure 5 indicates the
common switch functions are provided by the 677F

(Fig. 6) hybrid integrated circuit (HIC).

I_z A feature that is recognizable to the

short travel button which operates a

_ _ user of this dial is the "feel" of the

cIick disc switch similar to that used

Fig. 3--$72H3A Dial, Front View_l on many calculators.

2.04 The 72-type dial contains a polarity guard

eliminating the possibility of improper opera-

tion due to line reversals.

2.05 Each dial has eight spade-tipped leads (Fig. 6)

for connections to the telephone set network

and one screw terminal (D) located on the back side

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