Sound-Powered Telephone Maintenance

Replacing Handset Cords.-- To replace the cord

switchboard or switchbox line cutout switches will

on a sound-powered handset, you should use the

allow isolation of a faulty unit. For string circuits, you

following procedure:

should disconnect each set in sequence to isolate the

faulty unit.

1. Remove the faulty cord by unscrewing the

bushing and disconnecting the wires from the terminals.

LOSS OF SENSITIVITY.-- Loss of sensitivity, or

weakening of the transmission sound, is a gradual

2. Place the threaded bushing, washer, and

process and seldom is reported until the set becomes

grommet on the new cord.

practically inoperative. When a sound-powered

3. Insert the cord into the handset and connect the

telephone is in good condition electrically yet the sound

wires to the terminals.

is weak you should replace the transmitter unit. If this

4. Screw the bushing into the handset tightly to

procedure does not remedy the trouble, then you should

secure the cable.

replace the receiver units.

5. Test the set for proper operation.

To test a headset for loss of sensitivity, you should

Replacing Tinsel Cords.-- To replace a tinsel cord

depress the talk switch and blow into the transmitter. If

on a sound-powered telephone headset-chestset, you

the set is operating properly, you will hear a hissing

should use the following procedure:

noise in the receiver units. You should listen to one

receiver unit and then the other. In most cases, the loss

1. Open each unit connected to the cord that is to

in sensitivity is in the transmitter unit and might be

be replaced.

caused by a displacement of the armature from the exact

2. Before disconnecting the cord, make a diagram

center of the air gap between the pole pieces.

showing the color coding of the wires.

To test a handset for loss of sensitivity, you should

3. Disconnect both ends of the cord.

blow air into the transmitter. It is not necessary to press

4. Remove the screw that holds the tie cord, or

the talk switch because the transmitter and receiver are

untie the cord if it is secured to an eyelet.

permanently connected in parallel. If no sound is heard,

5. Unscrew the entrance bushing, if provided, and

either the transmitter or the receiver is defective. The

pull the cord through the port.

easiest method to determine which unit is defective is to

have someone talk into another phone on the circuit

6. Place the threaded entrance bushing, metal

while you listen to both the transmitter and receiver of

washer, and rubber gasket on the new cord and insert

the cord into the entrance port. The cord should be long

the handset. If the talker's voice is heard on one of the

units but not the other, you should replace the unit on

enough to allow slack after it is connected.

which the voice is not heard because it is defective. If

7. Secure the tie cord so that it takes all the strain

the talker's voice cannot be heard on either unit, and the

off the connections; otherwise the wires might be pulled

telephone circuit being used is known to be good, the

from their terminals.

fault may be traced to the line cord, switch, or internal

8. Connect the wires to the terminals.

handset circuits.

9. Screw the entrance bushing on the entrance port,

REPLACING CORDS.-- When replacing cords,

drawing the bushing up tightly to secure the cable and

you should always use prepared cords, if possible.

to seal the port.

Handset cords fitted with terminals at both ends are

10. Close the unit after all connections have been

available through standard stock. Tinsel cord cut to the

visually checked.

proper lengths and fitted with terminals for use with the

11. Test the set for proper operation.

various types of headset-chestset transmitter and

receiver units are also standard stock items. DCOP 1 1/2

If prepared cords are not available for repairing

headset-chestsets, you can make them from bulk tinsel

cord is used between the junction box and the plug on a

cord using the following procedure:

sound-powered headset-chestset.

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