Waveform Analysis

TM 11-6625-1702-35

b. TUNE

INDICATOR b. Wiring defective ------- b. Perform continuity checks

to locate defect, and re-

does not extinguish

place or repair as re-

and coupler does not

quired.

stop tuning when FR

is removed.

Wiring to Z1 or to S3 de- Perform continuity checks to

5 RF wattmeter test Power indications

fective Z1 defective.

incorrect.

locate defects in wiring.

(para 4-9).

Repair or replace as re-

quired. If no defects are

located in wiring, replace

Z1.

2-6. Waveform Analysis

u r e m e n t s are presented in the chart in (2)

a. T h e t u n i n g s i g n a l f r o m t h e a n t e n n a

below. Use these measurements and the

coupler may be monitored at MOTOR PULS-

s c h e m a t i c diagram (fig. 53) to isolate trou-

ING SIGNAL jack J1 of the test set with an

bles.

oscilloscope.

T h e normal waveform obtained

Caution: When measuring voltages, use

at the test jack is shown in figure 44,

tape or sleeving (spaghetti) to insulate the

b. Since the antenna coupler used in testing

entire test prod, except for the extreme tip. A

the test set is known to be working properly,

momentary short circuit can ruin a transistor.

a departure from the normal waveform in-

(1) The voltage readings will always be

dicates that trouble exists in the test set. Check

obtained as given in (a) through (d) b e l o w .

a l l wiring between the point at which the

(a) Make voltage measurements using

waveform is observed and the antenna coupler.

Multimeter ME-26B/U or equivalent.

(b) M a k e a l l v o l t a g e m e a s u r e m e n t s

2-7. Isolating Troubles

with respect to chassis ground.

a. General. Once a trouble has been localized

(c) M a k e a l l v o l t a g e m e a s u r e m e n t s

to a functional circuit in the test set, it may

with dc power (28 volts) applied. Do not c o n -

be necessary to perform further tests to isolate

nect any other test equipment such as the fm

the trouble to a particular component. When a

transmitter or the antenna coupler.

trouble has been localized to a functional cir-

(d) M a k e a l l v o l t a g e m e a s u r e m e n t s

cuit, review the principles of operation of that

with the MANUAL TUNE switch and the

circuit (paras 1-8 through 112 ). Then per-

METER FUNCTION switch set to OFF.

form resistance and continuity checks ( b

( 2 ) Resistance measurements are made

b e l o w ) and voltage resistance measurements

with power disconnected from the test set. Use

(c below) as required.

a multimeter, and make all resistance measure-

Caution: Do not make resistance and con-

ments with respect to chassis ground.

tinuity checks with power applied to the test

set. DO not make any measurements that would

Transistor

Resistance

DC voltage

place the multimeter across test set meter M1.

31.6K

12.9

26K

b. Resistance and Continuity Checks. W h e n -

13.0

13.2

25.9K

e v e r required, perform resistance and con-

t i n u i t y checks on resistors, capacitors, and

0.2

15K

wiring with a multimeter.

19.9K

0.2

c. Voltage and Resistance Measurements.

When required, voltage and resistance meas-

0.2

19.9K

1 meg.

urements are taken at the emitters, bases, and

collectors of Q1, Q2, and Q3. The normal meas-

2-6