TM 11-6625-1514-15
Section V
Paragraphs 5-1 to 5-8
SECTION V
MAINTENANCE
5-1. SCOPE.
procedures. If an adjustment or replacement of parts
5-2. This section contains complete instructions for
is made without following instructions or understanding
the effects, further trouble shooting may be complicated.
repairing and calibrating the voltmeter. This material
is covered in the following groups of paragraphs: b. Do not remove tubes when the voltmeter is turned
on. Before replacing tubes refer to paragraph 5-10.
Lead
Paragraph
Topic
5-5. TEST EQUIPMENT REQUIRED.
5-3.
Precautions
5-6. The test equipment required for complete testing
5-5.
Test Equipment Required
5-7.
of the voltmeter is listed in figure 5-1. Equivalent
Meter Zero Adjustment
5-9.
instruments may be substituted for those listed.
Cabinet Removal
5-10.
Tube Replacement
5-7. METER ZERO ADJUSTMENT.
5-13.
Replacement of Special Parts
5-17. Trouble Shooting
5-8. The meter is properly zero-set when its pointer
5-20. Testing the Power Supply
5-22.
rests over the zero calibration mark on the meter scale
Testing Voltmeter Performance
5-24.
when the instrument is 1) at normal operating tempera-
Calibration and Frequency Response
ture, 2) in its normal operating position, and 3) turned
Adjustments
off. Adjust the zero-set if necessary, as follows:
5-3. PRECAUTIONS.
a. Allow the voltmeter to operate for 20 minutes so
that the meter movement will reach normal operating
5-4. Observe the following precautions:
temperature.
a. Make no adjustments and replace no parts in the
b. Turn the voltmeter off and allow one minute for all
voltmeter except as described in one of the following
capacitors to discharge.
INSTRUMENT TYPE
REQUIRED CHARACTERISTICS
USE
DESIGNATION
Electronic
0 to 300 a-c and d-c volts;
Voltage and resistance ME -26 B/U or
Multimeter
accuracy of ±3% or better;
measurement.
H-P 410B
input impedance 100 megohms.
Oscillator 10 cps to 300 kc; 3 volts
Signal source for
output into 50-ohm load. testing and calibration
H-P 200S
Voltmeter Calibrator
400-cps output voltage;
Calibrating voltmeter
(Precision Voltage 0.001 to 300 volts at mid-frequencies.
H-P 738BR
Source)
in 10-db steps ±0.2%; 0.1 to
1.0 volt in 0.1 volt steps ±0.2%.
Frequency 300-kc to 4-mc range;
Calibrating voltmeter
Response 3 volts output into 50-ohm load; frequency response.
H-P 739A
Test Set 10-db steps, 0 to 70 db.
Oscilloscope or
10-cps to 4-mc range.
Trouble shooting by
AC Voltmeter
H-P 160B or
signal tracing.
H-P 400D
Variable Adjust line voltage between 103
Checking voltmeter
Transformer and 127V ac with 1-amp load.
operation with
CN-16/U or
varying line
Ohmite VT2
voltage.
D-C Current
Clip-on type measurement;
Checking load on
Test Set
current range up to 100 ma. power supply.
H-P 428B
(Milliammeter)
Figure 5-1. Test Equipment Required
00102-3
5-1
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