POWER AND RANGE SWITCHES

TM 11-6625-524-14-4

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Should a switch be suspected as being faulty, check the applicable contacts and

w i p e r ( s ) of the questionable switch section(s) for contact continuity. Also check

t h e wiring continuity between the suspected switch section (s) and their circuit

connection (s). Use the DC multimeter set to 1X ohms for continuity checks.

FEEDBACK, LINEARIZING AND CALIBRATION CONTROL NETWORK

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a. W i t h the voltmeter properly shielded (see paragraph 5-2) verify that all

l i n k s are connected to their original circuit board connections.

b. V e r i f y the RANGE switch is set to the 0.001V full scale position.

c. D i s c o n n e c t the oscillator from the probe. Adjust the SET REF control (volt-

meter) for a meter reading centered about the SET REF line.

d. R e c o n n e c t the oscillator to the probe. C o n n e c t the oscilloscope to amplifier

board terminal (3TP7). With 1mV applied to the probe, measure the waveshape and com-

pare to that as shown on the schematic diagram, figure F0-1. Should the level

g r e a t l y exceed that as shown, the network is probably faulty.

e . The following procedure may be used to troubleshoot the network:

f. Check the resistor and thermistor values, diode forward and reverse re-

sistances and the continuity of the network. Use a DC multimeter set to ohms.

g. Check the probe for resistance measurements as shown in. Table 5-1. Use the DC

multimeter set to ohms.

h. Disconnect the equipment as shown in figure 5-1.

SECTION III MAINTENANCE

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PROBE AND DIODE CARTRIDGE

T h e probe and diode cartridge are factory sealed and their disassembly is not re-

c o m m e n d e d . If defective, replace.

NOTE

Warranty on the probe and diode cartridge is void if tampered with.

I f the voltmeter fails to respond to RF signals and all other checks of the trouble

shooting sections have been made, t h e probe and/or diode cartridge may be at fault.

U s e the following procedure to verify the probe and diode cartridge's condition:

W i t h the voltmeter either in its cabinet or properly shielded (see paragraph 5-2)

e n e r g i z e and switch to the 0.001V full scale range position. Attach the probe,

terminate with the 50-ohm termination adapter but do not connect to a signal

source.

R o t a t e the SET REF control fully clock-wise, a normally operating voltmeter will

read between 50% and 100% of full scale. Disconnect the probe from the voltmeter,

a normal response is for the meter indicator to drift off-scale in either

direction.

S w i t c h to the 0.03V full scale range position.

The voltmeter should recover

r a p i d l y with the indicator returning to the SET REF position. These tests will

v e r i f y that the voltmeter is operating normally. The probe and/or probe diode

c a r t r i d g e is then at fault and should be individually tested as follows:

Change

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