Section II. MAINTENANCE OF TEST SET, ELECTRONIC CIRCUIT PLUG-IN UNIT AN/ARM-87

11-6625-467-34

the exact conditions under which the normal wave-

3-8. Oscilloscope Waveforms

forms were taken are duplicated.

c. A departure from the normal waveform indi-

a. The test set is composed mainly of oscillators

cates trouble between the point at which the wave-

and amplifiers which are most easily checked by the

form is observed to be normal and the point where

use of voltage level measurements. However, if it is

the abnormal waveform is observed. For example, if

more desirable to use an oscilloscope for signal trac-

the output of a transistor appears normal, and the

ing, refer to the schematic diagrams and check the

drive at the base of the second transistor is normal,

various test points in the circuit for the presence or

but no signal appears at the collector of the second

absence of a signal waveform. The 800 Hz inverter

transistor, it is an indication of trouble in the second

circuit (fig. FO-2) and the 500 kHz (fig. 3-35) and 30

MHz (fig. 3-44) switch circuits are most easily ana-

transistor stage. First check the transistor by the

use of the transistor tester (TS-1836/U) and replace

lyzed by the use of an oscilloscope. Figure 3-25

t h e transistor, if faulty. If the transistor checks

shows the waveforms a various points in these cir-

good, continue troubleshooting the circuit by the

cuits.

b. Use Oscilloscope UN/USM-182 to obtain the

use of table 3-2, voltage and resistance readings. Do

not overlook the fact that a short circuit in a follow-

waveforms. Before comparing the waveforms with

ing stage may reflect back and give the same indica-

the normal waveforms shown, carefully read the

tion.

notes on the waveform illustrations and insure that

Section II. MAINTENANCE OF TEST SET, ELECTRONIC CIRCUIT PLUG-IN UNIT AN/ARM-87

d. Switch Replacement. When replacing a multi-

3-9. General Parts Replacement Techniques

c o n t a c t rotary switch, always identify the wires

a. Replacement of Circuit Cards. The circuit

before removing them from the switch terminals.

cards in the test set are slot-coded to prevent insert-

White adhesive tape or masking tape marked with

ing a card in the wrong plug. Be very careful when

the switch terminal number works ideally. If it is

removing and replacing circuit cards in the card

necessary to remove cable lacing during the replace-

cage. Do not use excessive force or the cards may

ment of a switch, always replace the lacing alter the

become damaged. After a circuit card is repaired or

new switch is installed.

r e p l a c e d , always perform the adjustment proce-

dures applicable to that circuit card before return-

3-10. Printed Circuit Card Repair

ing the equipment to the user. Refer to paragraph

Parts mounted on printed circuit cards are bonded

3-10 for details on printed circuit card repair. Table

to the cards to protect the parts from humidity and

3-3 below lists the 13 circuit cards and the power

moisture. This bonding, or postcoating, also pro-

d e t e c t o r assembly. Listed adjacent to the circuit

tects the parts against excessive vibration in serv-

cards is the applicable adjustment procedure loca-

ice. If the repair process requires that a part be

tion. Some cards have more than one adjustment

p r o c e d u r e ; perform all the specified procedures

after a repair operation even if the repair did not

Table 3-3. Circuit Card Adjustment Procedures

affect the other circuits on the circuit card.

Adjustment

b. Soldering. Use a pencil-type iron with a capaci-

Ref

procedure

Circuit card name

ty of 20 or 25 watts. Check to see that the iron tip is

desig

(para No.)

isolated from the ac line (para 3-3). Do not use a

Load/500-kHz filter HV7 . . . . . . . . . . . .

3-28

soldering gun; damaging voltages can be induced

150-Hz oscillator/counter HU8, . . . .

3-22

i n t o the equipment. Solder transistor and diode

l-kHz/10-khz oscillator HU9. . . . . .,

3-23

leads quickly; s e m i c o n d u c t o r devices are easily

500-kHz fm oscillator HV2 . . . . . . . . . .

3-24,

3-25

damaged by heat. Whenever possible, use a heat

Audio amplifier/detector HU7. . .

3-20,

3-29

+28-volt regulator HU4 . . . . .

3-18,

3-30

s i n k (such as a long-nosed pliers) between the

High voltage power supply HU5 ., .,

3-31

soldering iron and the component.

-28-volt regulator HUB,...,..

3-19

c. Parts Replacement. Alway replace defective

Load No. l HV5 . . . . . . . . . . . . . . . .

None

parts with identical good parts. For replacing parts

3.975-5.925-MHz

oscillator

HV4

3-26,

3-27

Al0

o n the printed circuit cards, refer to paragraph

30-MHz

oscillator

HV8

3-32

All

A12

68-MHz oscillator HW2 . . . . . . . . . . . .

3-33

3-10. When replacing wiring or components on the

A13

3-21

RF amplifier/detector/switch HV3

chassis, choose the new wires or components as

3-34

A14

Power

detector

assembly

nearly like the original as possible.

3-37