TM 11-6625-2629-14&P
b. Band Switching Difficulty.
indicate a defective part, check the alignment of
the if and limiter stages (para 7-23 and 7-24).
(1) If the FREQUENCY RANGE-MC
switch does not operate properly, the trouble may
circuits and isolate the faulty component.
be with the detent mechanism (fig. FO-4). The
detent is properly positioned when it locks into
7-18. Additonal Troubleshooting Data
the notch on the rotor while all rotor contacts are
The items listed below will help the repairman
fully engaged in the mating contacts on the
troubleshoot the modulation meter.
tuning capacitor and output block.
a Dc Resistances of Tranuformers anti Coils.
( 2 ) If the FREQUENCY RANGE-MC
The dc resistances of the transformer windings in
switch rotates freely, check the setscrews (fig.
the modulation meter are Wed in table 7-5.
shutter to the shaft. They may have become
.
loose.
Section III. MAINTENANCE, ALIGNMENT, AND CALIBRATION
b. Replacement.
7-14. General Parts Replacement Techniques
(1) Place the oscillator unit on the chassis in
Most of the parts of the modulation meter can be
its approximate location.
reached and replaced easily without special tools
(2) Use the four screws removed in a (6)
or procedure. Observe the following precautions:
above to l hold the oscillator unit to the chassis
use a pair of pliers or some other device which will
(3) Replace tubes Vll, V12, and V18 and
act as a heat sink on the wire between the
their shields.
soldering iron and the diode. This protects the
(4) Reconnect P3 to J4. Connect the if cable
diode from excessive heat.
to the mixer housing (fig. 7-l).
b. Remove the cover to replace parts in the
(5) Place the FREQUENCY RANGE-MC
discriminator circuit (contained in T9, fig. 7-1). It
knob on the rotor shaft and replace the cross
may be necessary to remove the entire assembly
recessed screw. Be sure that the pointer is in the
from the chassis. When replacing the cover, be
correct position.
sure that the connections on C73 do not touch the
(6) Place the TUNING knob on the tuning
can. These connections are at high potentials to
shaft and tighten the setscrews.
ground.
7-16. Disassembly and Reassembly of Local
7-15. Removal of Oscillator Unit
Oscillator
a Removal.
(1) Loosen the setscrews on the TUNING
To replace any part of the oscillator remove the
knob and pull off the knob.
oscillator unit from the chassis (para 7-15).
(2) Remove the cross receesed screw from
a. Disassembly.
the FREQUENCY RANGE-MC knob and pull off
NOTE
the knob.
Disamemble the oscillator unit only as far
(3) Disconnect P3 from J4 by unscrewing
as needed to replace a worn or broken
P9. Disconnect the if cable from the mixer
component.
housing (fig. 7-l).
(1) Rotate the rotor (23) to a position be-
(4) Remove the shielde and tubee Vll, V12,
tween two bands, to disengage the contacts at-
and V13.
tached to the tubeholder assembly (17) and
(5) Hold oscillator assembly and remove the
capacitor contact assembly (28). This will prevent
four screws on the underside of the chaeeia that
damaging them.
hold the omillator unit to the chassis. (fig. 7-3).
hub (2) Loosen the setscrews (24) in the rotor
(6) Carefully lift the oscillator unit from the
.
.
chassis.
7-12
