Hammarlund SP-600-JX-21 User manual

HANDBOOK
OVERHAUL INSTRUCTIONS
RADIO RECEIVER
MODEL SP-600-JX-21
(HAMMARLUND)
PUBLISHED UNDER AUTHORITY OF THE SECRETARY OF THE AIR FORCE
Air Force OC, 29 JUI 65-250-~eprint
15 JANUARY 1956

T.O. 31 R2-4-101-3
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LIST OF REVISED PAGES ISSUED
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T.O. 31R2-4101-3 Table of Contents
VII
VIII
TABLE OF CONTENTS
*n Page
INTRODUCTION ...................................................................................... 1
DESCRIPTION AND LEADING PARTICULARS ................................ 1
...
1.1 . General ............................................ ..................... .......... 1
1.3 . Pertinent Information ..................................................................... 1
1.5 . Difference Data Sheets ............................................................... 1
TEST EQUIPMENT AND SPECIAL TOOLS ........................................ 3
2.1 . TestEquipment ............................................................................. 3
2.3 . Special Tools .......................................................... , ............... 3
MAINTENANCE BEYOND CAPABILITIES OF FIELD
..................... 5
3.1 . General ........................................................................................ 5
3.5 . Specialized Maintenance Procedure ...................... ......................... 5
DISMANTLING AND DISASSEMBLY
............................................... 7
4.1 . Dismantling ................................................................................ 7
4.5 . Disassembly ................................................................................. 7
........................................... CLEANING ........................................ ..... .. 11
5.1 . Overall ............................................................................................ 11
.................................
. .............................................. 5.3 Electrical Parts , 11
................... 5.5 . Mechanical Parts ................................................. .... 11
........................................................ .
5.8 Preservation After Cleaning 11
............................................................................................. INSPECTION 11
..............................................................................................
. 6.1 General 11
6.5 . Chassis Assembly Inspection ....................................................... 12
6.8 . SubassemblyInspection .................................................................. 12
............................... .............................................
6.10 . Parts Inspection , 13
...
.......................................
. ........................................... 6.31 Servlce Llrn~ts , 15
REPAIR AND REPLACEMENT
............................................................. 17
7.1 . General .............................................................................................. 17
................................................
7.3 . Switch Base and Spring Assembly 17
. .
7.7 . Selectivity Switch .............................................................................. 17
...
7.9 . Retrop~cal~zation .............................................................................. 17
REASSEMBLY AND TESTING OF SUBASSEMBLIES AND
ASSEMBLIES
......................................................................................... 19
8.1 . General ........................................................... .. ............... , .. 19
8.3 . Reassembly of Tuning Unit Assembly ...................................... ...
19
8.5 . Resoldering and Retropicalization ............................ ... .............. 20
8.7 . Testing of Subassemblies and Assemblies .................................... 20
REASSEMBLY AND TESTING OF COMPONENTS
..........................
9.1 . General ............................................................................................
.....................
9.3 .
Reassembly of Chassis and Tuning Unit Assembly
9.5 . Reassemblyof Chassis and Panel Assembly ...................................
9.7 . Reassembly of R-f Tuners .............................. .......... ......................
9.9 .
Reassembly of Plug Connector Assemblies ....................................
9.11 . Reassembly of Radio Receiver .............................. ... ..................
9.13 . Testing .......................................................................................
................................................... ....................... FINAL REASSEMBLY .. 23
..................................
INSPECTION. TESTING. AND PACKAGING 23
11-1 . General ....................................................................................... 23
11-3
.
Minimum Performance and Test Values .................... .. .......... , . ,
23
. .......................................................................................
11-5 Packaging 23
DIFFERENCE DATA SHEETS
................................................................ 23

List of Illustrations
List of Tables
T.O. 31R2-4-101-3
LlST OF ILLUSTRATlONS
Figure Page
..
..............................................
1-1. Radio Receiver, Model SP-600-JX-21 11
.........................
2-1. Special Tools to Reassemble R-f Strip Assembly 3
...........
2-2. Special Tools to Reassemble Tuning Unit Shie!d Assembly 3
2-3. Special Tools to Reassemble Turret Rotor Assembly
......................... 4
2-4. SpecialTools to Reassemble Gear-train Assembly ............................. 4
4-1. Gear-train Assembly, Exploded View ................................................ 8
LlST OF TABLES
Table Page
I Special Tools Required for Overhaul ........................................... 3
I1 Identification of R-f Tuners ............................................... 22
Figure 1-1. Radio Receiver, Model SP-600-JX-21

T.O. 31R2-4,-101-3
Introduction
Section
I
INTRODUCTION
This handbook has been published to furnish maintenance depot personnel with
descriptive information and overhaul instructions for Radio Receiver, Model SP-600-
JX-21, manufactured by the Hammarlund Manufacturing Co., Inc., New York 1,N.Y.
The handbook has been prepared in accordance with Specification MIL-H-6814A
(ASG). Abbreviations used are in accordance with Air Force-Navy Aeronautical
Bulletin No. 261. Electrical and electronic symbols used in the schematic diagrams
conform to Standard JAN-STD-15.
For additional information on the radio receiver, the following publications
should be consulted:
Title Publication No.
Handbook Operation Instructions, Radio Receiver, T.O. 31R2-4-101-1
Model SP-600-JX-21
Handbook Service Instructions, Radio Receiver, T.O. 31R2-4-101-2
Model SP-600-JX-2 1
Illustrated Parts Breakdown, Radio Receiver, T.O. 31R2-4-101-4
Model SP-600-JX-2 1
SECTION I
DESCRIPTION AND LEADING PARTICULARS
1-1. GENERAL. that all possible precautions are taken at the factory to
hi^ publication comprises overhaul instructions provide each receiver for use in perfect condition, need-
for Radio Receiver, Model SP-600-JX-21 (figure 1-1), les~unsoldering and replacement of parts during over-
manufactured by the Hamrnarlund Manufacturing Co.,
'laul 'perations be avoided-
Inc., New York 1,N. Y.
1-5. DIFFERENCE DATA SHEETS.
Note
1-6. Sections I through XI of this handbook apply to
Refer to the applicable handbook of service Radio Receiver, Model SP-600-
JX-21. Additional models
instructions for a detailed description and lead- will be covered in Section XI1 by the use of Difference
ing particulars of the receiver. Data Sheets.
1-3. PERTINENT INFORMATION.
1-7. Overhaul instructions for any models to be in-
1-4. The receiver r-f coils, r-f chokes, and all soldered cluded in Section XI1 will be the same as the procedures
connections are treated with fungicidal varnish. All metal given in Sections I through XI, except for the specific
parts in contact conform to the electrochemical series so differences noted by the applicable Difference Data
that corrosion is kept to a minimum. In view of the fact Sheets.

T.O. 31 R2-4-101-3
Section II
Paragraphs 2-1 to 2-4
SECTION II
TEST EQUIPMENT AND SPECIAL TOOLS
2-1. TEST EQUIPMENT.
the work outlined in this publication are listed in table
2-2. No special test equipment is required to align, I. The table refers to the figure and index number of the
adjust, or final test the radio receiver. To facilitate the illustration
for each tool, the tool part number, and the
testing of the receiver a test position should be main-
tained, provided with the appropriate test equipment tool name. The application column in the table briefly
and fabricated cables described in the applicable hand- denotes the receiver subassembly or parts to which the
book of service instructions. respective tools are applied when the receiver is over-
2-3. SPECIAL TOOLS.
hauled. The manner of use and application of each tool
2-4. The special overhaul tools required to perform is outlined in detail in paragraphs 7-6 and 8-4.
TEST I. SPECIAL TOOLS REQUIRED FOR OVERHAUL
Figure 8
Index No. Port No. Nomenclature Use and Applicafion
2-l(1) T7982-5 Pin, locating R-f strip subassembly.
2-1 (2) T7982-6 Bar, line-up
2-1 (3) T7982-7 Pin, locating
2-2 (1) T8331-1 Swage Contact spring and partitions, tuning unit shield.
2-2 (2) T8331-2 Mounting, seat
2-3(1) T7644 Jig, fixture Turret rotor subassembly.
2-3(2) T8332 Rod Turret rotor and tuning unit shield, line-up.
2-3(3) T8333 Wrench, spanner Turret rotor subassembly nuts.
2-4(1) T8335
Jig
2-4(2) T8334 Pliers Band dial location.
"C" washers, crimping.
1. Locating pin
2. Line-up bar
3. Locating pin
1. Swage
2. Seat mounting
Figure 2-1. Special Tools to Reassemble R-f Figure
2-2. Special Tools to Reassemble Tuning
Strip Assembly Unit Shield Assembly

Section I1 T.O. 31R2-4101-3
Figure 2-3. Special Tools to Reassemble
Turret Rotor Assembly Figure
2-4. Special Tools to Reassemble
Gear-train Assembly

T.O. 31R2-4-101-3
Section Ill
Paragraphs 3-1 to 3-10
SECTION III
MAINTENANCE BEYOND CAPABILITIES OF FIELD
3-1. GENERAL.
3-2. The specialized maintenance and repair activities
within the scope of depot overhaul are based on receiver
trouble-shooting procedures supplementary to those pro-
vided in the applicable handbook of service instructions.
The data are useful in the step-by-step procedures used
to determine specific circuit failures.
3-3. Before resorting to the specialized maintenance and
repair procedures, ascertain whether the receiver fault
is due to any of the following causes:
a. Damage or miswiring.
b. Short circuits between parts or to ground, prior or
subsequent to the reassembly of the subassembly or part
to the receiver.
c. Faulty parts whose fault is only evident when the
part has been allowed to warm up by turning the
receiver on.
3-4. All of the receiver circuitry, apart from that con-
tained in the r-f strip, is accessible. When the receiver
fault is isolated to the r-f strip, the subassembly must be
L
removed from the receiver for repair or replacement. To
determine the specific cause of the r-f strip failure re-
quires part-by-part analysis to isolate the faulty part. The
r-f strip removed for repairs may be externally recon-
nected to the receiver through means of insulated test
clip leads, to render accessible its circuitry for purposes
of analysis. When this is done, do not attempt to recon-
nect the four-gang variable tuning capacitor unless it too
is external to the receiver. The r-f tuners for the fre-
quency band desired may be seated in the r-f strip steatite
base
"V" contacts.
I WARNING
Keep the receiver turned off when externally
reconnecting the r-f strip to the receiver.
3-5. SPECIALIZED MAINTENANCE PROCEDURE.
3-6. The specialized maintenance procedure outlined
in each of the following categories differs from that
outlined in the handbook of service instructions. The
- /
extent of difference is that the parts in subassemblies are
all analyzed while contained in the receiver which is
turned on and a1lowed.a warm-up period of at least five
minutes.
3-7. RESISTOR FAILURE. To determine whether a
resistor is normal, determine first its circuit function,
noting whether it is isolated or whether it has a d-c
voltage drop across it. If the former, determine first,
utilizing a volt-ohmmeter, that it has no d-cvoltage across
it, possibly due to the failure of its associated isolating
capacitor, and then measure its resistance. Turn the re-
ceiver off to measure the resistance of any resistor. To
measure the resistance of resistors R32, R33, R48, R53,
R60, R61, R66, R68, R93, R94, R95, R96, R97, R111,
and R112, unsolder one resistor lead to isolate the resis-
tor from the resistor network of which it is part.
3-8. CAPACITOR FAILURE. To determine whether
a capacitor is abnormal, i.e. open, shorted, or leaky,
determine first its circuit function, noting whether it is
used for d-c voltage isolating or filtering purposes, for
tuning purposes, or to provide a low-impedance series
or shunt path for the signal itself.
3-9. OPEN CAPACITOR. An open capacitor cannot
provide a low-impedance path for the signal, be used to
tune a circuit to resonance, or cannot provide filtering
action. However, it will keep a circuit isolated. In the
isolating instance, the capacitor usually carries the signal
or other a-c voltages across it so that an open capacitor
can always be analyzed with regard to its circuit function.
To do this, apply an appropriate signal to the applicable
test point so that the capacitor under consideration, if
normal, may perform its function; utilize an a-c vacuum-
tube voltmeter or a cathode-ray oscilloscope indication to
determine whether .the capacitor is open. Each of the
following circuit indications, as applicable, provides for
checking an open capacitor.
a. When the capacitor is in series with the signal path
of the receiver, but open, its input signal indication is
much higher than its output signal indication, to ground
in each instance.
b. When the capacitor provides a return path to
ground for the signal, but is open, its ungrounded ter-
minal is at an a-c voltage level above ground.
c. When. the capacitor is used to tune a circuit to
resonance, but is open, the circuit inductance cannot be
adjusted for resonance.
d. When the capacitor is used to provide audio filter-
ing action, but is open, its ungrounded terminal will
provide indication of excessive ripple, as compared to
when the open capacitor is shunted by a normal capacitor.
e. When the capacitor is used to provide decoupling
action in r-f circuits, but is open, more signal indication
may be observed across its terminals, as compared to
when the open decoupling capacitor is shunted by a
normal capacitor.
3-10. SHORTED CAPACITOR. A shorted capacitor
may be rapidly identified because it cannot have a d-c

Section Ill
Paragraph 3-1 1
T.O. 31 R2-4-101-3
or a-c voltage drop between its terminals. Each of the
following circuit indications, as applicable, provides for
checking a shorted capacitor.
a. When the capacitor circuit connection is such that
one of its terminals is normally at some d-c voltage above
ground, it cannot provide a d-c voltage indication to
ground when a volt-ohmmeter or d-c vacuum-tube volt-
meter is used to make the test.
b. When the capacitor circuit connection is such that
only an a-c voltage is normally effective at its terminals,
possibly due to the signal, and the capacitor is shorted,
no vacuum-tube voltmeter or oscillograph indication
across the capacitor results. In this instance, the signal
ltsually is not evident in the receiver circuitry immedi-
ately following the capacitor.
c. When the capacitor is used as a trimmer capacitor,
and is shorted, it has no trimmer effect on tuned cir-
cuits. In this instance and when the capacitor is used
to provide for the parallel resonance of adjustable core
tuned circuits, the signal is usually no longer evident
in the subsequent receiver circuitry.
d. When the capacitor is shunted by a resistor as is
the case in certain of the r-f tuners, and it is suspected
that the capacitor is shorted, the shunted resistor, meas-
ured for resistance as outlined in paragraph
3-7, will
determine whether the capacitor is shorted.
3-11. LEAKY CAPACITOR. When a capacitor is sus-
pected of being leaky, avoid having to unsolder one of
the capacitor terminals from the receiver by utilizing
every possible receiver switch and/or tube means to
isolate the capacitor terminal. To determine whether a
capacitor is leaky do the following:
a. Turn the receiver off.
b. Adjust the volt-ohmmeter to its highest ohmmeter
range and connect it across the capacitor. If the capacitor
is good the ohmmeter pointer will flick over slightly
--.-.
and gradually drop back to infinity.
c. Now reverse the test prods. Note that if the ohm-
meter deflection is twice that obtained in step b, with the
pointer then returning to the position indicating infinite
resistance, the capacitor is good. If the pointer does not
go back to infinite resistance indication, the capacitor is
leaky and should be replaced. This test is not reliable for
capacitors whose capacitance value is less than 0.05 uf.
Note
When the capacitor is an electrolytic type, one
reading will show low resistance and the other
much higher. If the higher resistance is not
over 100,000 ohms and comparable to that of a
spare capacitor, the electrolytic capacitor must
be replaced.
Make sure to turn the receiver on at least 15
minutes before making the test so that any
electrolytic capacitor dielectric film deteriora-
tion may be repaired by subjecting the capacitor
to its d-c working voltage. Turn the receiver
off, and discharge the capacitor before making
a resistance measurement.

T.O. 31R2-4-1Q1-3
Section IV
Paragraphs 4-1 to 4-7
SECTlQN IIV
DISMANTLING AND DISASSEMBLY
4-1. DISMANTLING.
4-2. PRELIMINARY PROCEDURE.
a. Remove the cartoned radio receiver from its
wooden shipping box and then unpack it completely.
b. Dismantle the radio receiver top cover and bottom
plate from the receiver chassis and panel assembly.
c. Dismantle the plug connector assemblies, the elec-
tron tube complement, the front panel controls, the
frequency control unit switch arm and eccentric drive
assembly, the front panel assembly, etc from the receiver
chassis and panel assembly.
d. Strip the main dial indicator and mounting, hoth
main and vernier dials, hoth side plates, etc from the
receiver chassis and tuning unit assembly.
4-3. DISMANTLING THE TUNING UNIT ASSEM-
BLY. To dismantle the tuning unit assembly from the
receiver chassis and tuning unit assembly, use the fol-
lowing step procedure:
<L
a. Unsolder two green/white leads, one each from
terminal strips El4 and E17.
b. Unsolder two blue/black leads from second mixer
transformer T2.
c. Unsolder white/black, red/white, blue/red, yellow/
black, and red/green leads from terminal strip E13.
d. Unsolder two red/green, one green/red, and one
yellow/red leads of the main wiring cable from con-
version switch S4.
e. Remove two No. 10-32 screws and one stud post
assembly, on either side of tuning unit assen~bly,which
screw into nut plate brackets through clearance holes in
gear-train plate and chassis proper.
f. Remove one No. 10-32 screw in angle bracket on
rear of tuning unit assembly, which passes through
clearance hole at back of chassis proper.
g. Lift out the tuning unit assembly.
4-4. The tuning unit assembly comprises several sub-
assemblies which may be dismantled from it and then
separately disassembled. These are the following:
. --,
a. The mixer plate coil assembly TI.
b. The r-f wiring assembly, i.e., the r-f strip.
c. The variable capacitor, i.e., the eight section, four-
gang tuning capacitor.
d. The gear-train assembly.
e. The 24 r-f subassemblies, i.e., the r-f tuners.
4-5. DISASSEMBLY.
4-6. DISASSEMBLY OF GEAR-TRAIN ASSEMBLY.
The gear-train assembly (figure 4-1) is disassembled in
accordance with the following step-by-step procedure.
a. Remove cam and hub assembly (1).
b. Remove slide spring (2), then remove four screws
(4) and four spacers (5) and remove the slide and roller
assembly (3).
c. Remove two detent springs (6) and lever and roller
assembly (7).
d. Remove screw (9) and two screws (10) used to
mount bearing plate (8). Then remove cam and hub
assembly (ll), shaft and gear assembly (12), flywheel
and shaft assembly (13), and idler (14).
e. Loosen nut (16) and remove bearing screw (15)
and ball bearing (17).
f. Remove two screws (19) and bearing plate (18).
g. Remove three screws (20) and then remove the
shaft and gear assembly comprised of hub (21), shaft
and gear assembly (23) and retaining ring (22). If
required, remove the retaining ring (22) and disassemble
the hub (21) from shaft and gear assembly (23).
h. Remove three screws (25) and three posts (24).
i. Remove dial, hub and gear assembly (26), gear and
hub assemblies (27 and 28), and main dial hub and gear
assembly (29) by removing the associated retaining rings
(30). Then remove gear and drive pin assembly (31)
and ball bearing (32).
j. Remove two screws (33) and then remove the gear
plate assembly comprised of two gears (34), two washers
(36), two retaining rings (35), and plate and pin assem-
bly (37).
k. Remove switch spring (38) and lever assembly (39).
1. Remove three screws (42) and three lockwashers
(43), and then remove gear (40) and gear (41). Remove
three screws (45) and three lockwashers (46), then
remove huh (44). Remove wavy washer (47), screw (49),
mounting disc and shaft assembly (48), and three con-
tact springs (50).
m. Remove three spider springs (51). Remove two
screws (53) and nut plate (52). Remove ten screws (55)
and disassemble base plate and spider assembly (54)
from tuning unit shield assembly (56).
4-7. DISASSEMBLY
OF CHASSIS. The chassis assem-
bly may be disassembled in any sequence desired subse-
quent to the removal of the three-section, four-pole,

I
1. Cam and hub assembly 27. Gear and hub assembly
2. Slide spring
28. Gear and hub assembly
i. Slide and roller assembly 29. Main dial hub and gear assembly
i. Screw 30. Retaining ring
5. Spacer 31. Gear and drive pin assembly
6. Detent spring
32. Ball bearing
-. Le~erand roller assembly
33. Screw
8. Bearing plate 34. Gear
9. Screw 35. Retaining ring
1~. Screw 36. Washer
11. Cam and hub assembly 37. Plate and pin assembly
12. Shaft and gear assembly 38. Switch spring
13. Fllnheel and shaft assembly
39. Lever assembly
14. Idler 40. Gear
15. Bearing screw 41. Gear
16. Nut 42. Screw
I-. Ball bearing 43. Lockwasher
18 Bearing plate 44. Hub
19. Screw 45. Screw
2fJ. Screw
21. Hub
22 Retaining ring
23. Shaft and gear assembly
24 Post
25. Screw
26. Dial, hub and gear assembly
52. Nut plate
46. Lockwasher
47. Wavy washer 53. Screw
49. Screw 55. Screw
50. Contact spring
48. Mounting disc and shaft assembly 54. Base plate and spider assembly
56. Tuning unit shield assembly
51. Spider spring
Figure 4-1. Gear-train Assembly, Exploded View

T.O. 31R2-4-101-3 Section
IV
Paragraphs 4-8 to 4-10
6-position rotary selectivity switch assembly, which is
removed first to get at all chassis wiring underneath it.
This switch assembly comprises rotary switch S5A, B, C,
three resistors, eight insulated electrical wires, five bare
electrical wires, and two pieces of vinylite tubing which
cover in part two of the bare electrical wires. The switch
assembly is removed in preference to removing the rotary
L-
switch proper to minimize the unsoldering during re-
moval.
4-8. Certain other subassemblies and parts of the chassis
assembly, likewise, may be removed in such a manner as
to minimize unsoldering during removal.
These are:
a. The audio output transformer, which is removed
with all the electrical wire leads and the one capacitor
that are soldered to it.
b. The antenna input socket, which is removed with
the black electrical wire that is soldered to it.
c. The meter a-f adjustment potentiometer, which is
removed with the electrical wire jumper that is soldered
to it.
d. Both the large octal sockets which are removed
with the electrical wire leads, resistors, and capacitors
that are soldered to them.
4-9. The r-f strip, i.e., the r-f wiring assembly, which
is contained
in the tuning unit assembly, has its tube
sockets removed with the bare electrical wires that are
soldered to certain of the tube sockets. Also, the isolan-
tite switch bases of the r-f strip are removed with the
bare electrical wires, certain resistors, and certain capaci-
tors soldered to them, which do not interfere with the
removal.
4-10. The frequency control unit and the audio filter
assembly, which are contained in the chassis and panel
assembly of the receiver, may be dismantled from the
receiver at any stage in the overall disassembly proce-
dure outlined. The frequency control unit socket and
selector switch are disassembled by unsoldering the bare
electrical wire leads soldered to them from the socket
and switch contact terminals; also, the bare electrical
wire common to the six crystal sockets is unsoldered
subsequent to the removal of the crystal socket plate
carrying the crystal sockets. The audio filter assembly is
disassembled subsequent to its dismantling as a unit.

T.O. 31R2-4-101-3
Sections V-VI
SECTION V
CLEANING
5-1. OVERALL.
5-2. Clean the radio receiver by blowing out with dry,
filtered compressed air at a pressure of approximately
100 psi. Accessible parts may be wiped with a clean cloth
or dusted with a small dry brush.
5-3. ELECTRICAL PARTS.
5-4. When the radio receiver is dismantled and its
subassemblies are disassembled, blow out, wipe, and dust
all wired electrical parts as outlined in paragraph 5-2
for the overall receiver. The air pressure at the subassem-
bly or part may be decreased by increasing the distance
between the air nozzle and the work.
WARNING
Wear goggles to protect eyes from dust.
5-5. MECHANICAL PARTS.
ii
5-6. Clean all mechanical parts such as the chassis, side
plates, shields, screws, etc by brushing with cleaning
solvent, Federal Specification P-S-661, or trichlorethylene,
Specification MIL-T-7003. To remove corrosion use No.
000 sandpaper as well, then wipe with a clean cloth.
5-7. Dirty gears are cleaned best with a pipe cleaner
or small brush dipped in any one of the cleaning fluids
mentioned in paragraph 5-6. The variable air trimmer
capacitors may be cleaned by soaking them bodily in
trichlorethylene, and then blowing them out. This applies
to the r-f trimmer capacitors even when assembled to
their isolantite bases, with r-f coils, resistors, and all
other fixed capacitors removed.
5-8. PRESERVATION AFTER CLEANING.
5-9. R-F COILS AND CHOKES. Tfeat all r-f coils and
chokes used in the radio receiver by dipping in bakelite
resin, fungicidal varnish conforming to Specification
MIL-V-173.
5-10. FOUR-GANG VARIABLE AIR CAPACITOR.
The four-gang variable air capacitor end bearings are
lubricated at the factory with lubricating grease, Specifi-
catior, MIL-L-7711. Relubricate in the remote instance
when the need arises.
SECTION VI
INSPECTION
6-1. GENERAL.
6-2. The raido receiver is inspected by careful observa-
tion and feel for any possible abnormal physical indica-
tion. Even though a mechanical defect appears trivial, it
must be repaired at
the first opportunity so that it does
not develop cumulative receiver abnormalities leading to
serious failure. Periodic receiver overhaul provides an
opportunity for qualified inspection personnel to deter-
mine the need for immediate repair of the receiver.
'.-,
6-3. INSPECTION TECHNIQUE. To properly inspect
each radio receiver, the inspector must thoroughly famil-
iarize himself with the receiver as follows:
a. Determine first the normal appearance of the radio
receiver by carefully noting the appearance of each sub-
assembly and part and their assembled inter-relationship
as outlined in paragraphs 4-1 through 4-10 and 8-1
through 8-6. Until such time that the normal detailed ap-
pearance of the receiver is committed to memory, compare
the receiver part by part with a receiver known to be in the
condition in which it left the factory. Carefully observe
the color and finish of all parts, their relative placement,
the dress of each electrical wire, the quality of the crimp-
ing of each soldered wire, the amount of solder used to
make a soldered joint, and the manner and location of
those soldered joints providing electrical grounds. Note
that all soldered joints, all r-f coil assemblies, and all
r-f chokes are tropicalized as evidenced by their brownish
fungicidal varnish coating. Note that the 8 nuts at the
2 escutcheons on the front panel, the 12 nuts at the 6
crystal sockets on the frequency control unit, the bearing
screw
(5, figure 4-I), and each nut used to mount each
pin on each of the
24 r-f tuner subassemblies is coated
with varnish. The varnish is used as an aid to secure each
nut since not too much strain can be used to tighten
each assembly.

Section VI
Paragraphs 6-4 to 6-9
T.O. 31R2-4-101-3
b. Determine next the manner in which the receiver 6-5. CHASSIS ASSEMBLY INSPECTION.
operating controls activate the mechanical means used
to perform each control function. Get the feel of each
control and commit it to memory. Note that the tuning
control is flywheel balanced and that it is free to turn
even when the tuning lock is locked. Note that the
two indicators for the main dial and the one indicator
for the vernier dial all simultaneously present zero dial
indications when the four-gang variable air capacitor
is fully meshed. Note that the movable main dial fre-
quency indicator pointer locates at the frequency scale
on the main dial corresponding to the frequency band
indented and whose frequency range is that shown on
the dial visible through the small window contained in
the front panel. Note the manner in which the frequency
control unit crystal switch arm and eccentric drive assem-
bly drives the two switches coupled to the drive assembly,
the orientation
of the drive arm and the effect of the
small helical spring used. Note the spring-return action
of the meter switch. Note the extent to which the gears
(34, figure 4-1) mesh with those they engage and the
hole provision in the bearing plate
(8) to get at one of
the screws (33). Note that the lubrication used on the
gear-train assembly is barely visible. Note, by feel, the
tightness of the adjustable tuning cores and trimmer
capacitors, but make sure not to disturb their adjustment
settings.
6-4. RECEIVER ABNORMALITIES. Inspect the re-
ceiver with regard to each of the following possible
categories of abnormality:
a. Aging: Aging of the receiver is indicated by non-
positive operation of movable parts whose normal func-
tion during movement or when indented is controlled
through the use of springs, cams, gears, ball bearings, or
precise bearing fits to trued machined shafting.
b. Burning: Overheating of the receiver is indicated
when parts comprising it show discoloration, blistering,
bulging, or smell burnt.
c. Leakage: Evidence of oil or insulating compound
at the terminals of sealed-container parts provide the
earliest possible evidence of receiver leakage. The leak-
age may be evident too at pin holes and/or breaks in the
container itself.
d. Corrosion: Evidence of receiver corrosion is the
oxidation (rust) which forms on surfaces, screws, nuts,
etc, usually where different metal areas are in contact.
e. Dust, dirt, etc: The need for cleaning the receiver
is evaluated best by noting the extent to which dust,
dirt, etc has accumulated at electron tube socket termi-
nals, resistor boards, and other not too easily accessible
soldered joints and corners in the receiver.
f. Looseness: The need for tightening any sub-assem-
bly or part comprising the receiver is evaluated by check-
ing the suspected part for tightness. When checking
attaching hardware such as nuts and/or screws, consider
the assembly tight when no more than a 90-degree turn
may be taken up in the attaching part. Make sure to
reseal those nuts listed in paragraph 6-3 whenever occa-
sion arises to tighten any one of them.
6-6. OVERALL: Apart from the careful inspection of
the radio receiver for physical damage evident by obser-
vation, the receiver controls should all be tried to see
that they function properly. Then inspect the receiver
chassis assembly for the following conditions:
a. Switch the selectivity switch from position to posi-
--
tion and inspect each switch contact for evidence of
charring of the bakelite switch wafers; if charred, replace
the switch.
b. Check at all tube socket terminals for possible
arcing and charring between terminals; if charred, replace
the tube socket concerned. To look at the tube sockets
on the r-f strip, remove the r-f coil assemblies, and use a
small dental mirror.
c. Check the conversion switch contacts for possible
arcing and charring between contacts; if charred, replace
the switch.
6-7. SWITCH BASE AND SPRING ASSEMBLY. Re-
move the
'20 r-f tuner subassemblies on five of the six
receiver frequency bands, doing this with the receiver
chassis and panel assembly turned upside down. Engage
the pin contacts of the four r-f tuner subassemblies kept
in the tuning unit assembly with the
"V" switch contacts
assembled to the isolantite bases contained in the r-f
strip, using the band change control on the front panel.
Note that the "V" switch contacts are spread by the pin
contacts and that the pin contacts center up in the "V"
V'
switch contacts; also check to see that none of the "V"
switch contacts are broken, and that the pin contacts in
the
24 r-f tuner subassemblies are not loose. Replace any
broken "V" switch contacts and tighten any loose pin
contacts, as outlined in paragraph 7-5.
6-8. SUBASSEMBLY INSPECTION-
6-9. For purposes of receiver overhaul, inspect each
subassembly removed from the receiver, following the
procedures outlined below, as applicable.
a. Check the dress of each part, such as capacitors,
resistors, coils, chokes, terminal boards, and the electrical
wire lead lengths used. Check the clearance between parts
and their mountings, the encoded values and tolerances
of resistors and capacitors; also check the part numbers
of coils, r-f tuner subassemblies, and the reference symbol
circuit designations on transformer shield assemblies, etc.
b. Check the quality of each soldered joint and the
location and manner of making each specific subassem-
bly ground connection.
c. Check the tightness of staked terminals, screws,
nuts, clamps, and all parts comprising the subassembly.
d
Check each spring for resilience and proper length, cur-
vature, etc. Check adjustable tuning cores for proper
operation and, if bent, note the extent to which the
tuning core enters the coil it tunes, so that it may be so
readjusted prior to reassembly, thereby not necessitating
too much of an adjustment during the subsequent align-
ment.

T.O. 31R2
J. Shake out loose metal and other particles. Make
sure none remain wedged in the assembly. Look closely
for metal or other foreign matter, especially between the
stator and rotor plates of the variable air trimmer capaci-
tors. Mesh all trimmer capacitors, checking for even
meshing and spacing between plates.
L-
e. Carefully check bakelite and melamine boards for
scratches and cracks; make sure isolantite bases, insula-
tor feed-throughs, and crystal porcelain holders are not
minutely cracked or chipped.
f. Check multiple coil assemblies mounted on the
same form for spacing. Make sure the start and finish
leads on all coil assemblies are properly connected. Check
each coil for continuity and for broken strands. Check
for nicks or scratches on coils and chokes, also check to
see that the fungicidal varnish coating is not punctured.
g. Check the possibility of the parts of the sub-
assembly shorting to other subassemblies or to the
receiver chassis, when assembled. Make sure the pilot
lamps, meter board, etc mount rigidly.
h. Check to see that the metal finish on each of the
plated parts contained in the subassembly has the proper
finish. Check to see that any excessive fraying of wire
insulation is cut off and touched up with insulation
compound (varnish), SpecificationMIL-C-13811.
6-1 Q. PARTS INSPECTION.
6-11. For purposes of receiver overhaul, each part con-
-
tained in the receiver, when removed, may be inspected
in accordance with the applicable procedures outlined
below. When a part fails to meet any one of the con-
siderations listed for it, reject it; but in instances where
the part only requires cleaning have it cleaned prior to
reinspection. All repaired parts must be reinspected prior
to use.
6-12. ELECTRON TUBE INSPECTION. To inspect
each of the electron tubes in the receiver, remove the
tube shield, if any, and in the instance of two of the
tubes remove the top-hat type of tube retainer associated
with each.
a. Check the firmness of each tube in its socket. Press
the tube into the socket, exerting only normal pressure.
When the tube is properly seated it should be held firmly
in place, as evidenced by feel.
b. Let the tubes cool off before removing them from
their sockets in the receiver. Use the appropriate tube
remover to remove miniature tubes; also, straighten the
lniniature tube pins in the appropriate pin straightener
before trying to insert the miniature tube into its socket.
-,
When inserting the miniature tube do so with the top
-
of the tube socket visible so that the tube pins may be
properly aligned in relation to the socket.
c. Inspect the glass envelope of each tube for dirt;
also check to see that the tube envelope is not loose.
Make sure that miniature tube pins are not loose or
broken, being careful not to bend the pins during removal
or insertion of the miniature tube. Check to see that the
gliiss envelope is not chipped ;~t the pins.
Section VI
Paragraphs 6-10 to 6-16
6-13. RESISTOR INSPECTION. Apart from the vit-
reous-enameled bleeder resistors R85, R72, and R73 in
the B+ rectifier supply, which are of the usual lug type
and rated respectively at 10, 20, and 20 watts, all the
resistors in the receiver are of the pigtail, fixed composi-
tion insulated type, rated at
1/2, 1/3 or 1 watt.
a. Inspect the coatings of R85, R72, and R73 for
signs of cracking and chipping, especially at the ends
of each.
b. Examine the body of each resistor for blistering,
discoloration, and breaks caused by overheating.
c. Inspect all resistor leads for dirt, dust, corrosion,
and looseness. Check the security of all mountings. Once
a resistor of the pigtail type is unsoldered, do not re-use
if the leads were initially cut short since the point of
entry of the lead may be partially or completely broken.
Also, the heat applied during unsoldering and resolder-
ing may damage the resistor or change its value.
6-14. AIR-DIELECTRIC VARIABLE CAPACITOR
INSPECTION.
a. Inspect the capacitor for dust, dirt, lint, and poor
or broken soldering.
b. Inspect the capacitor plates for visible damage such
as nicks and bending. Also, by meshing the rotor and
stator plates, make sure that during meshing the plates
do not touch and that they remain reasonably centered
at all times with regard to plate spacing.
Never tamper with the plates of the main tun-
ing capacitor.
c. Inspect the capacitor plate mountings, terminals,
and overall for looseness, wear, breaks, or other damage.
Make sure that the main capacitor ball bearings and the
trimmer capacitor rotor spring assembly in each instance
provide for smooth, firm rotor and stator meshing.
6-15. PIGTAIL-LEAD CAPACITOR INSPECTION.
a. Inspect each pigtail-lead type capacitor for lead
looseness. Do this by applying a firm steady pull to each
capacitor lead in turn, making sure that the tension
applied is not excessive.
b. Inspect each capacitor for discoloration, breaks,
chipping, and evidence that the molded casing does not
completely enclose the capacitor assembly.
c. Inspect the three oil-filled, tubular, metal-case
capacitors (C137, C144, and C163) for evidence of oil
leakage at the pigtail-lead solder terminal connections,
for the quality of the solder terminals, and for corrosion.
6-16. TERMINAL-TYPE CAPACITOR
INSPECTION.
a. Inspect the capacitor terminals for insulation cracks,
looseness, corrosion, and evidence of leakage of elec-
trolyte in the case of dry electrolytic capacitors.
b. Inspect the metal case container of each unit for
bulges, dents, cracks, and other damage of any kind.
Make sure the terminal lugs on the three-section elec-
trolytic capacitor (CIGIA,
B, C) are not loose.

Section VI
Paragraphs 6-17 to 6-23
T.O. 3 1 R2-4,- 10 1-3
6-17. FUSE INSPECTION. The fuse complement of
the radio receiver comprises two holder type fuses. One
is of the slow blow "Fusetron" type rated at 1.6 amperes
and the other is of the instantaneous type rated at 3/8
ampere. Throw blown fuses away.
a. Inspect each fuse for loose ends and cracks or breaks
in their glass encasings.
b. Inspect each fuse holder and holder cap for evi-
dence of burning, charring, corrosion, and dirt; make
sure the spring tension in the fuse holder is strong
enough to butt the fuse up against the back of the fuse
cap, noting that the cap spring tension only provides for
holding the fuse to the cap for insertion or removal.
6-18. INSULATOR INSPECTION. The two insulators
used in the radio receiver are of the feed-through type.
That on the frequency control unit is made of steatite
and has a white glazed finish while that on the r-f strip
is made of white isolantite.
a. Inspect the steatite and isolantite insulators for the
possible deposit of foreign matter since an insulator is
only as good as the condition of its surface.
b. Inspect the steatite and isolantite insulators for
fine-line surface cracks where moisture and dust will
accumulate and form a leakage path. Make sure these
insulators are clean, without cracks, or chips, and that
the quality of the soldering and spinning used for mount-
ing is good.
6-19. SWITCHINSPECTION. The switch complement
of the radio receiver comprises switches of both the
enclosed and open types.
a. Inspect the mechanical action of each switch and
look for dirt, dust, and corrosion on all exposed parts.
In the instance of enclosed switches, check the action of
the switch by actuating the control knob or toggle. In
the instance of the spring-return meter switch, note the
amount of pressure needed to overcome the spring ten-
sion. In the instance of the crystal selector switch, make
sure that the detent action is positive acting and that
the front panel control knob activates the frequency
control switch contained in the frequency control unit
in each of its eight positions but only activates switch
S3 on the base plate in its two most counterclockwise
positions.
b. Inspect the swich base and spring assembly, cov-
ered in paragraph 6-7, and the three-section selectivity
switch contacts for looseness, dust, dirt, and corrosion.
Make sure that the rotors of each switch make contact
with the stators as evidenced by the visible spreading of
the stator contacts when engaged by the rotors. Do not
pry the leaves of the stator contacts apart in any manner
whatsoever, other than by the the engagement of the
switch rotors themselves.
6-20. R-F COIL AND CHOKE INSPECTION. Apart
from the r-f coil or transformer contained in each of
the
24 r-f tuner subasserhblies, the radio receiver has an
i-f output autotransformer, 11 r-f chokes, and 15 r-f
transformers or coils, the latter contained in the various
transformer subassemblies comprising the receiver. Four
of the latter, contained in the first and second i-f trans-
formers, are each contained in two iron cups for pur-
poses of shielding. No attempt should be made to remove
said iron cups; the coil assembly itself is to be replaced
whenever the need for the replacement of these r-f coils
arises.
a. Inspect each r-f coil, r-f choke, and shielded r-f coil
L
for cleanliness, the quality of soldering, the firmness of
terminals, coil turns, and the assembly, and fungicidal
varnishing, as applicable. Make sure that there are no
nicks or cracks in the coil forms or in the fungicidal
varnish coating of each coil. Remember that the coil
form functions as a high-voltage insulator whose require-
ment is the utmost in cleanliness.
b. Inspect each r-f coil and r-f choke for the conti-
nuity of each winding. Check the d-c resistance of each
winding as tabulated in the applicable handbook of
service instructions. Note that the secondaries of the
three r-f coils in the r-f tuner subassemblies used on the
1.35-3.45 mc frequency band of the receiver and the
four iron-cup-shielded i-f coils each use No. 15/44 litz
wire. In all other applicable instances No. 7/41 litz wire
is used.
6-2
1. POTENTIOMETERS. The radio receiver utilizes
potentiometers as r-f gain, audio gain, bfo injection, a-f
meter adjustment and r-f meter adjustment controls.
a. Inspect the metallic parts of each control for dust,
dirt, and evidence of corrosion. Make sure that the unit
has no mechanical defects such as loose terminal lugs,
.
loose body assembly, or a loosely keyed shaft.
b. Inspect the insulated body of the unit for cracks
and chipping.
c.' Inspect the operation of the control, making sure
that the shaft turns smoothly but firmly in its mounting.
6-22. TERMINAL BOARDS. The radio receiver utilizes
19 terminal boards for purposes of part mounting.
a. Inspect the mechanical assembly of each terminal
board for loose brackets, terminals, eyelets, rivets, etc.
b. Inspect the terminal board bakelite or melamine
insulation for cracks, breaks, dirt, charring, or break-
down of the insulation due to the corrosion of the metal
parts of the terminal board assembly.
6-23. CABLES. The main wiring cable is pre-fabricated
before assembly to the receiver chassis and comprises,
apart from numerous electric wires, five shielded insu-
lated leads.
a. Inspect the insulation of each visible electrical wire
and cable contained in the main wiring cable, and that
of the shielded lead cables, noting whether the insulation
is cracked, deteriorated, cut, kinked, or strained.
i/
b. Inspect each end of each lead for broken strands,
frayingof the insulation, and damage due to poor solder-
ing and crimping. Make sure that partially or completely
broken strands are not hidden by the insulation.
c. Inspect to see that the braided shield of all the
shielded insulated leads does not short to the shielded
conductor.

Section VI
Paragraphs 6-24 to 6-32
6-24. CONNECTORS, PLUGS, AND SOCKETS. The
antenna input and the i-f output connectors, the phones
jack, and the
6 crystal and 20 electron tube sockets
comprise the connector and socket complement of the
receiver.
a. Inspect the insulation of each for dirt, dust, corro-
. sion, charring, and cracks.
L
b. Inspect contacts for collected dust, corrosion, breaks,
and other than normal looseness.
c. Inspect each connector and socket, checking the
contact provided when its complementary plug, crystal,
or tube is inserted. Increase, when needed, the spring
tension of the phones jack. When a tube socket has
replaceable contacts which require replacement, replacing
the contacts may prove more practical than replacing the
tube socket.
6-25. METER. The tuning meter contained on the front
panel of the receiver has a 200-microampere d-c move-
ment and is provided with two scales.
a. Inspect the meter for cracked or broken cover glass,
dents in the case, a warped dial, and
a bent or broken
pointer.
b. Inspect the meter for dust, dirt, and corrosion on
the meter case and terminals. Remove the meter cover
and repeat the inspection for the inside of the meter
cover and the meter proper.
c. Inspect, by checking the meter adjustment screw,
L
to see that the pointer may be properly set to the initial
dial indication from either direction. Make sure that the
adjustment spring is not caught on the adjustment arm.
d. Test the meter for balance by incorporating it in a
circuit such that it will indicate +20 db on the r-f scale
at
88 microalnpers +-5 percent, and will repeat this
indication.
6-26. CRYSTALS. The 3.5 mc oscillator crystal and the
455 kc i-f filter crystal, apart from any specially ordered
h-f-o crystals used for fixed-frequency crystal-controlled
operation, comprise the crystal complement of the re-
ceiver.
a. Inspect each crystal for dust, dirt, cracks, breaks,
and corrosion.
b. Inspect the 455 kc crystal terminals, to which are
soldered pigtail-type leads, and the 3.5 mc oscillator
crystal
flat strip terminals, to make sure that they are
tight. Also inspect the quality of the pigtail lead solder-
ing in the instance of the former and the terminal silver
plating of both. Make sure that the cover spring retainer
for the 3.5 mc oscillator crystal provides sufficient ten-
-
sion to firmly seat itself.
c. Inspect the h-f-o crystals for dust, dirt, dents, poor
soldering of metal case, corrosion of case and pin termi-
nals, cracked terminal pin insulation, and loose terminal
pins. These type
CR-18/U crystals conform to Specifica-
tion MIL-C-3098, but have stamped on the top and one
side the signal frequency in kc for which they are
intended.
6-27. TRANSFORMERS AND CHOKES. The receiver
audio output and power transformers and the two
Bf
rectifier filter chokes are all cased similarly. The power
transformer is oil impregnated and hermetically sealed.
The audio transformer is oil filled. The two filter chokes
are hermetically sealed.
a. Inspect for blistering, bulging, or leakage from
containers and from terminals.
b. Inspect for broken, cracked, or charred insulation
at the terminals. Inspect to make sure terminals are not
loose.
c. Inspect for dust, dirt, lint, or foreign material
between terminals since same will absorb moisture which
in time provides a leakage path for high voltage break-
down between terminals.
6-28. FUNCTIONAL MECHANICAL PARTS. The
mechanical parts such as coupling shafts, couplings, drive
arm and eccentrics, gears, lever and roller, dials, cams,
control knob and dial assemblies, springs, etc, which
provide for the proper mechanical functioning of the
receiver, all require inspection.
a. Inspect for dust, dirt, and corrosion.
b. Inspect for damage, such as cracks, distortion, poor
etching, etc, as applicable.
6-29. MECHANICAL PERFORMANCE STAND-
ARDS. The mechanical performance standards of the
radio receiver when subjected to normal use are most
easily evaluated in terms of the minimum (electrical)
performance standards of the receiver. Normal use
implies that the receiver is not subjected to extreme
vibration, extremes in temperature and/or humidity,
or exposed to dust, dirt, etc. When the receiver is sub-
jected to abnormal use, an evaluation of the abnor-
malities or damage sustained determine the extent to
which the receiver, certain of its subasse~nblies,or parts
require overhaul.
6-30. LIFE OF THE RECEIVER. The life of the
receiver is directly dependent on the preventive main-
tenance performed to keep the receiver in its normal
mechanical and electrical state. The replacement of func-
tional mechanical and/or electrical parts, subassemblies,
etc, will not impair the subsequent life of the receiver.
6-31. SERVICE LIMITS.
6-32. The normal mechanical requirements of the re-
ceiver do not depend on the maintenance of parts within
specific service limits. Improper mechanical functioning
of the receiver, after long periods of normal use, may
be directly attributable to any one or more of the follow-
ing conditions.
a. Accumulations of dust, dirt, sediment, moisture and
the resultant corrosion, rotting, etc may cause the me-
chanical functioning parts of the receiver to become
clogged and subsequently worn so that they no longer
function normally.
b. Repeated use and mechanical fatigue may result in
the attaching hardware used to assemble the parts and

Section VI
Paragraph 6-33
T.O. 31R2-4-101-3
subassemblies to the receiver loosening up so that the
receiver mechanical functioning becomes impaired.
Further use may possibly result in damage to functioning
parts.
c. Repeated use and mechanical fatigue may cause the
numerous springs used in the receiver to no longer pro-
vide the necessary tension required for the normal func-
tioning of the receiver.
-
d. Repeated use under extreme conditions of vibration,
temperature, and humidity may accelerate conditions
which lead to abnormal mechanical functioning of the
receiver.
6-33. Whenever the receiver is subjected to overhaul
not directly due to abnormal use of the receiver, the
overhaul should include the following checks of the
receiver spring complement.
a. Check to see that each of the three contact springs
used on the partitions in the tuning unit shield assembly
are secure and make positive contact with the turret rotor
assembly.
b. Check to see that the wavy washer at the front end
of the turret rotor assembly is not loose such that it fails
to turn when the turret rotor assembly is indented from
one band to the next.
A loose wavy washer indicates
turret rotor endplay.
c. Check to see that the "U" shaped contact spring
at the rear of the turret rotor assembly provides firm
wiping contact with the turret rotor assembly and that
it is securely mounted.
d. Check to see that the receiver helical spring com-
plement, namely that at the pointer slide, the two at
the lever and roller detent assembly, and that at the con-
*d
version switch, have not lost their tension. Do this by
removing each spring in turn and noting that its unloaded
length is normal, i.e., the same as a new spare replace-
ment part.
e. Check to see that the three spider springs at the
gear-train assembly are not distorted in any way from
their normal unmounted shape by comparing them to a
new spare replacement part.
f. Check to see that the
24 r-f tuner subassemblies, the
24 r-f coils mounted on them, the h-f-o crystals, all
adjustable turning cores, and all trimmer capacitors, are
all provided with sufficient mounting tension from their
respective mounting springs, as evidenced by feel.
g. Check to see that the
"V" contact springs on the
band change switch base and spring assembly are not
broken and that they provide contact with the switch
pins on each of the r-f tuner subassemblies.

T.O. 31R2-4-101-3
Section VII
Paragraphs 7-1 to 7-13
SECTION VII
REPAIR AND REPLACEMENT
7-1. GENERAL.
7-2. The radio receiver comprises parts which are not
normally repaired. However, all parts comprising the re-
ceiver may be replaced. Of these, only the replacement of
each of the four base and spring assemblies, comprising
parts contained on the r-f strip, requires detailed instruc-
tions; refer to paragraph 7-3.
7-3. SWITCH BASE AND SPRING ASSEMBLY.
7-4. To replace any of the four base and spring assem-
blies comprising the stator of the band change switch,
first remove the r-f strip from the receiver. The reason
for the replacement may be that one of the six
"V" con-
tact springs on the four isolantite bases, or the bases
themselves, may be broken.
7-5. To replace a
"V" contact spring, remove the defec-
tive spring by first removing from the spring terminals
the solder which holds the spring in place in the isolan-
tite base. Then spring back the spring ear on each spring
leg in turn while pushing in a direction to remove the
spring. Note the spring ear locations on the spring to be
replaced. A new spring is then substituted for the defec-
tive spring removed, solder being used to retain it.
7-6. To replace a base and spring assembly, use the
line-up bar (2, figure 2-1) and locating pins (1 and 3)
to properly locate the base and spring assembly in rela-
tion to the rest of the r-f strip assembly. First, clear the
terminals of the isolantite base to be replaced by unsol-
dering the parts and leads soldered between them and
the r-f strip proper. Then unsolder the isolantite base
itself by removing the solder from the two eyelets by
means of which it is mounted to the r-f strip. Then
remove the isolantite base so that a new one may be used
to replace it. To properly locate the new isolantite base,
position the line-up bar (2) over it and the other isolan-
tite bases contained in the r-f strip. The line-up bar is
then located in relation to the isolantite bases soldered
to the r-f strip by means of the locating pins
(1 and 3)
which fit through the line-up bar holes and into the two
holes in each of the isolantite bases. Pin
(1) is used in
the smaller and pin (3) in the larger of the two holes in
each base. Position the new isolantite base so that when
soldered into place it is up against the line-up bar as are
all others. Remove the eight pins and the line-up bar.
Solder, to the new isolantite base, the r-f strip parts and
leads previously removed. Dress all leads as they were
previously by duplicating an r-f strip kept on hand as a
sample.
7-7. SELECTIVITY SWITCH.
7-8. The selectivity switch, which provides three crystal
and three non-crystal positions of receiver acceptance
bandwidth, is a three-section wafer-type switch assembly
which is assembled to the receiver with other parts, as
outlined in paragraph 4-7, assembled to it. It is recom-
mended that the switch assembly be replaced as a unit
instead of replacing any one of the wafers comprising it.
Replacement of a wafer is impractical, since its contact
construction assembly is peculiar to the receiver.
7-9. RETROPICALIZATION.
7-10. The soldered joints, r-f coils, and r-f chokes in
the radio receiver are all treated with fungicidal varnish
to render them moisture and fungus proofed.
7-11. Where the tropicalization of coils and chokes
requires some touch-up, use a small brush dipped in
moisture and fungus resistant varnish, Specification MIL-
V-173, to brush the varnish on the coil or choke, as
needed.
7-12. After resoldering a soldered joint, treat it by
brushing with varnish to completely cover the soldered
joint.
7-13. If any soldered joint is found to be poorly treated
with the varnish, it should be retreated to provide com-
plete varnish coverage.

T.O. 31R2-4'-101-3
Section Vlll
Paragraphs 8-1 to 8-4
SECTION VBll
REASSEMBLY AND TESTING OF SUBASSEMBLBES AND ASSEMBLIES
8-1. GENERAL.
8-2. The reassembly of the radio receiver comprises the
separate reassembly of the receiver chassis assembly and
the receiver tuning unit assembly. The receiver chassis re-
assembly need not follow a specific step sequence, other
than that the main cable wiring assembly be added first
and the selectivity switch assembly, referred to in para-
graph 4-7, be assembled last to the receiver chassis.
The frequency control unit and audio filter assemblies re-
ferred to in paragraph 4-8 may be reassembled to the
receiver chassis assembly prior to reassembling the
receiver tuning unit and chassis assemblies.
-
8-3. REASSEMBLY OF TUNING UNIT ASSEMBLY.
8-4. Before attempting to reassemble the gear-train
assembly, it is recommended that the following proced-
ures be understood fully so that the various reassembly
requirements are anticipated during the actual assembly.
Thegear-train assembly (figure 4-1) consists of a tuning
unit shield assembly (56) and a mounting disc and shaft
assembly (48), which are reassembled subsequent to the
addition of the base plate and spider assembly (54) to
the tuning unit shield assembly. The gears and parts
which comprise the gear-train are then built up on the
base plate and spider assembly to completely reassemble
the gear-train assembly.
a. Reassemble the tuning unit shield assembly (56),
noting that one of the three contact springs (50) is
associated with each reinforcing plate of the tuning unit
shield assembly. Seat the contact spring on the reinforcing
plate prior to assembly, and use the swage
(1, figure 2-2)
and seat mounting (2) to swage the reinforcing plate
metal to properly seat and firmly retain the spring.
b. Reassemble the tuning unit shield assembly (56,
figure 4-1) to the base plate and spider assembly (54),
using ten screws (55).
c. Reassemble the mounting disc and shaft assen~bly
(48) using the fixture jig (1, figure 2-3), the rod (2),
and the spanner wrench (3). Check the alignment of the
eight mounting discs by passing the rod through the
locating holes in the mounting discs. If the alignment
is correct, tighten the assembly with the spanner wrench.
d. Reassemble the mounting disc and shaft assenlbly
(48, figure 4-1) to the tuning unit shield assembly (56).
Position the wavy washer (47) at the front end of the
mounting disc and shaft assembly. Seat the combination
in the tuning unit shield and base plate and spider assem-
bly. Lubricate the hub (44) and screw (49) with lubricat-
ing grease, Specification MIL-G-3278, and secure the hub
to the front end of the mounting disc and shaft assembly,
using three screws (45) and three lockwashers (46).
Then mount the screw (49) which acts as the rear bearing
for the mounting disc and shaft assembly. Make certain
that the wavy washer is centered on the large nut at the
front end of mounting disc and shaft assembly before
tightening the two bearings. Lubricate both bearings
using lubricating grease, Specification MIL-G-3278. Add
the lever assembly (39) and switch spring (38).
e. Use the rod (2, figure 2-3) to line up the mounting
disc and shaft assembly (48, figure 4-1) and base plate
and spider assembly (54), by means of the alignment
holes provided in each assembly. Align the assemblies
so that the conversion-switch cam at the rear of the
mounting disc and shaft assembly is in its high position
when the switch blade of the conversion switch assembled
to the tuning unit shield assembly shorts its center contact
to the contact nearest to the edge of the tuning unit shield
xssembly (56).
f. Add the three spider springs (51) to the base plate
and spider assembly (54). Add the nut plate (52) to the
base plate and spider ~ssembly,using two screws (53).
g. Attach gears (41 and 40) to the hub (44), using
three screws (42) and three lockwashers (43). Attach
two gears (34) to the plate and pin assembly (37), using
two washers (36) and two retaining rings (35); attach
the.plate and pin assembly (37) to the base plate and
spider assembly (54) using two screws (33), but do not
tighten the assembly.
h. Attach three mounting posts (24) to the bearing
plate (18) with the three screws (25). Lubricate the shaft
of the shaft and gear assembly (23) with lubricating
grease, Specification MIL-G-3278, and assemble it to the
hub (21) using the retaining ring (22). Loosely mount
the completed assembly to the bearing plate (18) using
three screws (20).
i. Locate one ball bearing (32), lubricated with
lubricating grease, Specification MIL-G-3278, at the base
plate and spider assembly (54). Attach the bearing screw
(15) and nut (16) to the bearing plate (18). Position
the ball bearing (17), lubricated with lubricating grease,
Specification MIL-G-3278, at the bearing screw (15).
Position the gear and drive pin assembly (31) against
the ball bearing (17), and mount the bearing plate (18)
with the lubricated, loosely-mounted gear and drive pin
assembly
(31) to the two top posts (24), using two
screws (19).
j. Lubricate the five tempered shafts on the base plate
and spider assembly (54) with lubricating grease, Spec-
ification MIL-G-3278.
I<. Position the drive pin of the gear and drive pin
assembly (31) at the top of the slot in the base plate
and spider assembly (54). Add the gear and hub assetnbly