j.
Overhaul.
Normally, the highest degree of maintenance performed by
the Army in order to minimize tine work in process is consistent with quality
and economy of operation.
It consists of that maintenance necessary to re-
store an item to completely serviceable condition as prescribed by mainte-
nance standards in technical publications for each item of equipment.
Over-
haul normally does not return an item to like new, zero mileage, or zero
hour condition.
k
_. Rebuild.
The highest degree of materiel maintenance. It consists of
restoring equipment as nearly as possible to new condition in accordance with
original manufacturing standards.
Rebuild is performed only when required
by operational considerations or other paramount factors and then only at
the depot maintenance category.
Rebuild reduces to zero the hours or miles
the equipment,
or component thereof, has been in use.
l.
Symbols.
The uppercase letter placed in the appropriate column in-
dicates the lowest level at which that particular maintenance function is
to be performed.
B-3.
Explanation of Columns.
Listed below is an explanation of the columns shown in the maintenance
allocation chart:
a. Column 1, Group Number. Column 1 lists group numbers, the purpose
of which is to identify components, assemblies , subassemblies and modules
with the next higher assembly.
b.
Column 2, Functional Group.
Column 2 lists the noun names of com-
ponents, assemblies,
subassemblies and modules on which maintenance is
authorized.
c. Column 3, Maintenance Functions. Column 3 lists the lowest level at
which that particular maintenance function is to be performed.
d. Column 4,Tools and Equipment.
This column shall be used to specify,
by code, those tools and test equipment required to perform the designated
function.
e. Column 5, Remarks.
Self-explanatory.
B-2
Summary of Contents for 491
Page 4: ...i i Fig 1 1 The Type 491 Spectrum Analyzer ...
Page 24: ...2 16 Fig 2 17 Control set up chart ...
Page 34: ...Fig 3 1 Function block diagram of the Type 491 3 2 ...
Page 42: ...Fig 3 10 Block diagram of the video detector and vertical amplifier 3 1 0 ...
Page 48: ......
Page 53: ...Fig 4 4 Power Supply Circuit board assembly with wiring color code 4 5 ...
Page 54: ...Fig 4 5 Horizontal Display circuit board assembly showing color code to pin connectors 4 6 ...
Page 55: ...Fig 4 6 IF Control board assembly Wiring color code to pin connector 4 7 ...
Page 64: ...Fig 4 20A Tube subassembly removal procedure 4 16 ...
Page 65: ...Fig 4 20B Tube subassembly installation procedure 4 17 ...
Page 68: ...Fig 4 22 Power supply board assembly with component call out 4 2 0 ...
Page 69: ...Fig 4 23 Vertical Amplifier and Blanking board assembly with component call out 4 21 ...
Page 70: ...Fig 4 24 IF control board assembly with component call out 4 22 ...
Page 71: ...Fig 4 24 IF control board assembly with component call out 4 23 ...
Page 72: ...Fig 4 25 Horizontal display board with component call out 4 24 ...
Page 73: ...Fig 4 25 Horizontal display board with component call out 4 25 ...
Page 74: ...Fig 4 26 Phase lock board with component call out 4 26 ...
Page 88: ......
Page 90: ...Fig 6 1 Test equipment recommended for calibration of the Type 491 6 2 ...
Page 138: ......
Page 192: ......
Page 195: ...SECTION II B 3 ...
Page 196: ......
Page 200: ......
Page 201: ...SECTION 9 DIAGRAMS MECHANICAL PARTS LIST ILLUSTRATIONS ACCESSORIES ...
Page 202: ......
Page 203: ...9 1 ...
Page 204: ...9 3 ...
Page 205: ...9 5 ...
Page 206: ...9 7 ...
Page 207: ...9 9 ...
Page 208: ...9 11 ...
Page 209: ...9 13 ...
Page 210: ...9 15 ...
Page 211: ...9 17 ...
Page 212: ...9 19 ...
Page 213: ...9 21 ...
Page 214: ...9 23 ...
Page 215: ...9 25 ...
Page 216: ...9 27 ...
Page 217: ...FIG 1 9 29 ...
Page 218: ...FIG 2 REAR 9 31 ...
Page 219: ...9 33 FIG 3 IF CHASSIS PHASE LOCK ASSEMBLIES ...
Page 220: ...FIG 4 POWER CHASSIS 9 35 ...
Page 221: ...FIG 5 TIME DIV SWITCH OSCILLATOR ASSEMBLIES 9 37 ...
Page 222: ...FIG 6 CRT SHIELD ASSEMBLY 9 39 ...
Page 223: ...FIG 7 CABINET ASSEMBLY HANDLE 9 4 1 ...
Page 224: ...FIG 8 491 STANDARD ACCESSORIES FIG 8 491 STANDARD ACCESSORIES 9 43 ...
Page 225: ......
Page 226: ...PIN 028017 000 ...