TM 11-6625-1633-45
b. Replace the thermistor as follows:
NOTE
Do not tighten the two set screws holding
(1) Form the shape and size of the loop as noted in
the driver gear.
a(11) above.
(2) Rotate the center frequency selector handwheel
(2) Solder the new thermistor and assemble the
until the 600-1850 MC FREQUENCY MC counter indi-
probe.
cates the lowest possible frequency.
(3) Insert the thermistor probe into the coupling in
(3) Use the multimeter as an ohmmeter and connect
the position noted in a(8) above.
the leads between pins 2 and 3 of the potentiometer.
(4) Tighten the two set screws.
(4) Rotate the potentiometer drive shaft until the
(5) Solder the center conductor to the capacitor.
multimeter indicates approximately 50ohms.
(6) Replace the coupling cover.
(5) Tighten the two set screws holding the driver
(7) Slide the coupling into the yoke leaf springs.
gear, without shifting the potentiometer drive shaft.
(8) Assemble the thermistor yoke to the rf oscillator
(6) Disconnect the multimeter.
section.
(7) Assemble the tracking subassembly to the rf os-
cillator section (para 4-2).
CAUTION
(8) Perform the adjustment and alignment proce-
Be careful not to distort the loop by pushing
dures given in paragraphs 4-16, 4-17, 4-18 and 5-8.
the yoke all the way into the cavity.
4-5. Removal and Replacement of Thermis-
4-6. Removal and Replacement of
tor A4RT2 and A4RT3
Attenuator Probes
a. To remove either thermistor, proceed as follows:
a. To remove the low or high frequency attenuator
(1) Remove the rf oscillator section (para 4 - 2).
probes Z1 and Z2 proceed as follows:
(2) Remove the two screws holding the rack guide.
(1) Remove the rf oscillator section (para 4-2).
(3) Lift the rack and ease the thermistor yoke away
(2) Loosen the two set screws on the coupling.
from the rf oscillator section.
(3) Lift the attenuator probe up.
(4) Note the position of the thermistor loop relative
to the cavity.
b. Replace the attenuator probes as follows:
(5) Note the position of the leaf spring which holds
(1) Insert the attenuator probe in the coupling.
the thermistor coupling pressed against the yoke.
(2) Rotate the probe until the vertical scribe mark
(6) Slide the thermistor coupling out of the yoke.
faces the rear of the rf oscillator section.
(7) Remove the two cover screws and the coupling
(3) Tighten the coupling setscrews.
cover.
(8) Note the position of the thermistor loop with re-
4-7. Removal and Replacement of
spect to capacitors A4C2 and A4C3.
Microswitch A4S1 and A4S2
(9) Unsolder the connection between the center
conductor and the capacitor.
a. To remove either microswitch, proceed as follows:
(10) Loosen the two set screws holding the coupling
and pull the coupling away from the thermistor probe.
(1) Rotate the center frequency selector handwheel
(11) Note the exact shape and size of the loop.
to set the 600-1850 MC FREQUENCY MC
counter at 600 MHz
(12) Unsolder and remove the thermistor.
4-3
