Instruction manual

TM 11-6625-3017-14
SECTION 5
REPAIR
5.1 INTRODUCTION
This chapter contains information for the
localization and repair of faults. Performance limits
quoted are for guidance only and should not be taken as
guaranteed performance specifications unless they are
also quoted in the Data Summary section.
CAUTION See Maintenance, Sect. 4.1, for
precautions in handling semiconductors and for
advice on screw fasteners.
In the case of any difficulty, please write to or phone
the Marconi Instruments Service Division (see address
on back cover) or nearest representative, quoting the
type and serial number on the data plate at the rear of
the instrument. If the instrument is being returned for
repair, please indicate clearly the nature of the fault or
the work you require to be done.
5.2 FAULT LOCATION
General procedure
Methodical fault location can be performed at the
following three levels:
(i) Front panel functional checks for general
localization of a fault - see Sect. 5.2.2..
(ii) Internal checks for more detailed localization -see
Sect. 5.2.3 and figures 4.1, 4.2, and 5.5 through 5-
17.
(iii) Systematic calibration, which can be used to locate
a fault for which methods (i) and (ii) are inadequate
- see Sect. 5.4.
5.2.1 Test equipment required
See Table 5.1.
5.2.2 Front panel checks
As a first step in fault finding, the three following
tests will help you to verify nearly all the circuits of the
modulation meter and to localize the fault to certain
areas. These tests can be performed without removing
the cover. Failure of all three tests may indicate a faulty
power supply, in which case first check the fuses on the
rear panel.
(1) Turn the Function switch to SET CAL. If the meter
reads SET, the calibrator (A12) and the
discriminator, 1st and 2nd 1. f. amplifier, peak
reading voltmeter and associated circuits (A5 to
A10) are working. If there is no meter indication,
but the 2 kHz calibrator square wave can be seen
with an oscilloscope at the OUTPUT terminals, then
the peak reading voltmeter circuit, (A10), is faulty.
(2) Turn the Function switch to TUNE OSCILLATOR
AND ADJUST LEVEL. Connect a signal to the R.
F. IN socket and check that, by adjusting the
TABLE 5.1
Table 5.1
Test Equipment Required for Fault Location
Item Type Minimum specification Recommended model
a Signal Frequency: .1.5 MHz and between TF 995B2,
generator 4 and 1000 MHz TF 2006
Output: c. w., up to 100 mV.
b Multimeter 20 V d. c. at 20 kS/V Hewlett-Packard
250 V a.c. HP410A
c Measuring Bandwidth:5 MHz Hewlett-Packard
oscilloscope Sensitivity: 20 mV/cm HP 1700B
5-1