Figure 5-13.--Sound-powered telephone head set-chestset transmitter circuit.

Sound-powered handsets are usually repaired on

location because they are permanently connected. When

trouble develops in a sound-powered headset-chestset,

the usual procedure is for the operator to bring it to the

IC shop and exchange it for a good one. This procedure

provides each station with properly operating sets at all

times. The IC shop should maintain a log of all sets

turned in; this will aid in locating faulty circuits or

identifying operators who continually abuse their sets.

PRECAUTIONS.-- When repairing sound-

powered telephones, you should observe the following

precautions:

Figure 5-13.--Sound-powered telephone head set-chestset

Do not repair telephones on a dirty workbench.

transmitter circuit.

The magnets in the units may attract iron filings,

A short circuit in a single sound-powered

which are difficult to remove.

transmitter or receiver unit will render an entire circuit

Before disassembling a set, make a wiring

inoperative because all sound-powered telephones on

diagram showing the color coding, polarity, or

the circuit are connected in parallel. Operation of

terminal numbers of the lead connections.

Never alter the internal wiring of sets.

Always replace parts exactly as they were before

disassembly.

INSPECTION.-- You should make a routine in-

spection of sets before you begin to repair the sets to deter-

mine whether you should replace physically defective

parts. Many troubles may be located by inspecting the

set for damaged cord or insulation; cord pulled out of

units; loose units; defective or broken pushbuttons; and

broken or damaged parts, such as unit covers, neck strap,

chestplate, junction box, plug, and headband.

TRANSMITTER AND RECEIVER UNITS.--

Transmitter and receiver units are not repairable. If these

units become defective, they must be replaced. Both of

these items are standard stock items.

OPEN AND SHORT CIRCUITS.-- When testing

the units for open and short circuits, you should use a

low-voltage ohmmeter to avoid damage to the sound-

powered transmitter and receiving units. Continuity

tests may be made from the chestplate junction box on

sound-powered headset-chestsets. Figure 5-13 is an

illustration of the transmitter circuit of a sound-powered

telephone headset-chestset. Figure 5-14 is an illustration

of the receiver circuits. When testing the plug cable or

tinsel cords of a sound-powered headset-chestset, you

should disconnect them from the junction box. The

normal dc resistances of the sound-powered transmitter

and receiver units are 10 ohms and 62 ohms

respectively. If the plug cable and tinsel cords test out

Figure 5-14.--Sound-powwed telephone headset-chestset

recelver circuits.

satisfactorily, then you should check the capacitors.

5-15