SECTION 5 REPAIR

TM 11-6625-3017-14

SECTION 5

REPAIR

(iii) Systematic calibration, which can be used to locate

5.1 INTRODUCTION

a fault for which methods (i) and (ii) are inadequate

- see Sect. 5.4.

This chapter contains information for the

localization and repair of faults. Performance limits

quoted are for guidance only and should not be taken as

5.2.1

Test equipment required

guaranteed performance specifications unless they are

also quoted in the Data Summary section.

See Table 5.1.

CAUTION

See Maintenance, Sect. 4.1, for

precautions in handling semiconductors and for

5.2.2

Front panel checks

advice on screw fasteners.

In the case of any difficulty, please write to or phone

As a first step in fault finding, the three following

the Marconi Instruments Service Division (see address

tests will help you to verify nearly all the circuits of the

on back cover) or nearest representative, quoting the

modulation meter and to localize the fault to certain

type and serial number on the data plate at the rear of

areas. These tests can be performed without removing

the instrument. If the instrument is being returned for

the cover. Failure of all three tests may indicate a faulty

repair, please indicate clearly the nature of the fault or

power supply, in which case first check the fuses on the

the work you require to be done.

rear panel.

(1)

Turn the Function switch to SET CAL. If the meter

reads SET, the calibrator (A12) and the

5.2 FAULT LOCATION

discriminator, 1st and 2nd 1. f. amplifier, peak

reading voltmeter and associated circuits (A5 to

General procedure

A10) are working. If there is no meter indication,

but the 2 kHz calibrator square wave can be seen

Methodical fault location can be performed at the

with an oscilloscope at the OUTPUT terminals, then

following three levels:

the peak reading voltmeter circuit, (A10), is faulty.

(i)

Front panel functional checks for

general

(2)

Turn the Function switch to TUNE OSCILLATOR

localization of a fault - see Sect. 5.2.2..

AND ADJUST LEVEL. Connect a signal to the R.

F. IN socket and check that, by adjusting the

(ii)

Internal checks for more detailed localization -see

TABLE 5.1

Sect. 5.2.3 and figures 4.1, 4.2, and 5.5 through 5-

17.

Table 5.1

Test Equipment Required for Fault Location

Item

Type

Minimum specification

Recommended model

Signal

Frequency: .1.5 MHz and between

TF 995B2,

generator

4 and 1000 MHz

TF 2006

Output: c. w., up to 100 mV.

Multimeter

20 V d. c. at 20 kS/V

Hewlett-Packard

250 V a.c.

HP410A

Measuring

Bandwidth:5 MHz

Hewlett-Packard

oscilloscope Sensitivity: 20 mV/cm

HP 1700B

5-1