Section II. DIRECT SUPPORT TROUBLESHOOTING

TM 11-5820-509-35

Section II. DIRECT SUPPORT TROUBLESHOOTING

3-4. Troubleshooting Radio Receiver-Transmitter

3-3. Overall

RT-671/PRC-47 (A8)

a. General. When a malfunction of the radio set

CAUTION

occurs, the first step in correcting the deficiency is to

Do not apply power to the receiver-

sectionalize the cause to a specific functional area in the

equipment. The tests at operational and organizational-

transmitter

unless

operational

level have undoubtedly isolated the malfunction to

trouble symptoms are known and are

circuits within Radio Receiver-Transmitter RT-671/PRC-

of such a nature as to eliminate the

47. The sectionalizing tests listed below are arranged in

possibility of further damage when

an order of increasing circuit complexity and mechanical

the power is applied.

disassembly requirements within four major functional

a. Testing for Shorts.

areas of the radio set. These areas contain the power

(1) When to Check.

When any of the

supply, frequency generation, receiver-transmitter, and

following conditions apply, check for short circuits and

relay circuits. When performed in the order listed, these

repair any existing deficiency before applying power to

tests provide the maintenance technician with an orderly

the receiver-transmitter.

approach to the isolation of defective circuits and

(a) When the receiver-transmitter is

modules

within

the

interrelated

transceiver

being serviced and the fault symptoms are unknown.

subassembly. Test jacks are installed in the top of each

(b) When an inspection of fuses F1

module that permit connection of test instruments to

through F5 shows that a fuse has blown.

these circuits so that evaluation can be made of the

signals and voltage levels. Similar test points and jacks

(2) Conditions for Tests.

are accessible from the bottom of the main chassis that

(a) Disconnect all cables from the front

permit connection of test instruments to the power

panel of the receiver-transmitter.

amplifier and selected primary power circuits.

(b) Remove the dust cover from the

b. Use of Charts. The voltage and resistance

receiver-transmitter using the procedure of paragraph 3-

charts and the waveform diagrams shown in this section

11.

provide the maintenance technician with a go/no-go

(3) Measurements.

Using the multitester,

criteria that will assist him in locating the circuit

make the resistance measurements shown in the chart

deficiency and permit him to restore the circuit

below. Unless otherwise indicated in the point of

parameters) to values within the tolerances specified.

measurement column of this chart, all resistance

Before proceeding to any chart, the technician must

measurements are made from the test point shown to

establish the conditions for the test that are indicated,

chassis ground. The normal indication shown is an

must perform the initial equipment connections, and

average value and may vary from one unit to another

establish the radio set operating conditions called for in

and from one multitester to another. Any reading that

the procedure. Using this approach, the technician may

disagrees widely from the value shown will cause the

enter the chart at any functional area and proceed

maintenance technician to proceed to the isolating

through only that portion of the procedures that are

procedure indicated. Location of a defective part must

required to correct the deficiency.

initiate the repair procedure shown in section IV.

(4) Short Circuit Test.

Point of

measurement

Normal indication

Isolating procedure

Between A5J1 (fig. 3-4, 3-111 and

40.000 ohms (Will depend on setting of A5R4). Very low reading, improper

chassis ground,

adjustment of A5R4 or short at driver grid (A3C293). High

reading may indicate A5R4 open.

Between A5J2 and chassis ground.

50,000 ohms

(Will depend on setting of A5R3). Very low reading, shorted

feedthru C26 or inductor L122 in pa compartment. defective

XMTR PWR switch or shorted plate bypass C123. High

reading may indicate A5R3). open.

Between A5J3 and chassis ground.

10 ohms

Very low reading: shorted C208, C221, or C235 in FL2. shorted

primary at T3, or short in filament bypass C104. High reading

may indicate open winding at T1, defective tube V101, or

open hum balance control R121.

3-3