Tektronix 491 User manual

product
modification
050 - 0692 : ()2 (' )
M21303 , M22940
BAND
11
C
11
OSCILLATOR REPLACEMENT
For TEKTRONIX® Type 491 Spectrum Analyzers
Serial Numbers B010000-B272355
I l O 11
Solid State Band
11
C
11
Oscillator Assembly 119-0108-01
replaces vacuum tube oscillator 119-0108-00 which is
no longer available.
Use of the new solid state oscillator necessitates
the following changes:
1) The dial tape is replaced to assure oscillator
tracking on all bands.
2) A -20 Volt Power Supply is added for use with
the
new oscillator.
3) Di al coupling and osci 11 a tor mounting brackets
and hardware are replaced to accommodate the
changed dimension
of the new oscillator
assembly.
© 1974 , Tekt ronix, Inc.
All Rights Reserved. 7-23-75
Supersedes 050-0692-01
TEKTRONIX , SCOPE-MOBILE and ~ are registered trademarks of T ektron i x, Inc.
"- 4 "'? 9
3
1~1
Type
Page 1 of 9

PARTS INCLUDED IN PARTS REPLACEMENT KIT:
Quantity Part Number
Description
(1ea)
1 ea
l ea
ea
4 ea
l ea
1 ea
(l ea)
1 ea
1 ea
l ea
ea
ea
l ea
2 ea
l ea
l ea
2 ea
1 ea
l ea
l ea
1
ea
1 ea
1
ea
*NOTE:
119-0108-01
175-1529-00
175-1530-00
211-0008-00
407-1545-00
407-1546-00
670-0523-08
175-1531-00
175-0998-00
175-0999-00
210-0203-00
211-0021-00
211-0098-00
331-0376-00
361-0525-00
376-0029-00
376-0099-00
384-1265-00
386-1135-01
670-3500-01
670-4193-01
Assembly Oscillator* consisting of:
Osci1lator
9
RF
Cable, 50~ coax, 175-0323-00, 9 inches
w/131-0375-00 and w/131-0977-00
Cable,
50~ coax, 175-0323-00, 6 inches
w/131-0375-00 and w/131-0977-00
Screw, 4-40 X .250
Barcket, angle, oscillator front
Bracket, angle, oscillator rear
Wire, #22 stranded 175-0527-00 4 inch white
Wire, #22 stranded 175-0527-00 3 inches white-black
Assembly,
Oscillator Connector Circuit Board, consisting of:
Circuit Board, Oscillator Connector
Wire, ribbon
w/3 wires #26 stranded w/3 131-0707-00
connectors and w/l 352-0161-00 holder on one end only.
White-brown
and White-red 15 inches long soldered
to
circuit board and White-orange 7 inches long
from holder end.
Wire, #22 stranded 175-0527-00 4 inch White-red
Wire, #22 stranded 2 3/4 inches Wht-blk-yel w/2
131-0371-00 connectors
Wire,
#22 stranded 2 inches Wh t-brn w/l
131-0707-00 connector
Lug, so1 de r S E-6 long
Screw, 4-40 1.250
Screw, button
head 4-40 x .375
Tape, Frequency Di al
Spacer, Delrin® .781 inches long x .25 OD
Coupling shaft, rigid .312 OD x .5 lg x .128 ID
Coupling shaft, flex .437 long x .250
Shaft extension, .450 long x .125 OD
Plate, Oscillator mounting
Circuit Board, -20 Volt Power Supply
Circuit Board, Connector
The front and rear angle brackets are fastened to the Band
11
C
11
Osci1lator for
purposes of identification and orientation. They must be removed before the
oscillator can be insta1led. Save hardware.
® Delrin is a registered trademark of E. I. Dupont de Nemours Inc.
Page 2 of 9 050-0692-02

INSTRUCTIONS:
DISCONNECT THE INSTRUMENT FROM ITS POWER SOURCE!
CAUTION
Removing or reinstalling the instrument dust cover may be hazardous when the
instrument
is slid in or out of the dust cover. Remove or reinstall the dust
cover
as follows:
Pl ace the accessory cover on the instrument. Stand the instrument vertically
on the front cover. Remove the four plastic feet and the two thumbscrews and
slide the cover off of the instrument.
A. TO REMOVE OSCILLATOR ASSEMBLY
( ) l. Remove the Tuning knob and the Band Selector Switch knob. Remove
the screw below the tuning shaft.
Disconnect the following wires from the pin connectors on the
connector block on the chassis:
( ) 2. White-blue wire from Pin J.
() 3. White-violet wire from Pin I.
( ) 4. White-black wire from Pin E.
Disconnect the wires from the Oscillator connector Circuit Board
that connect to the TIME/DIV Switch as follows:
( ) 5.
White wire. (Unsolder shield of white-black coax from pin connector).
( ) 6. White-black-brown wire.
( )
7. White-brown-green-brown.
( ) 8. White-black wire. (Unsolder
center of white-black coax from Pin connector).
() 9. Disconnect all of the sub-miniature right angle coaxial connectors
from the oscillator assembly. To facilitate reassembly label the
coax cables and connectors.
( ) 10.
Remove the Band Switch bracket mounting screws which are accessible from
the bottom, (Note: You may have to remove the rail mounting bracket in
order to reach the top screw)
and the two nuts that fasten the driver
gear assembly to the front panel, and remove the oscillator assembly.
Page 3 of 9 050-0692-02

B. TO REMOVE THE BAND
11
C
11
OSCILLATOR
( )
( )
( )
( )
( )
( )
( )
( )
( )
1. Unsolder the Band
11
C
11
oscillator filament leads*. One from the Band 'B'
oscillator and one from the oscillator connector board.
2. Unsolder band C
B+ lead (orange wire) from connector board.
3. Loosen the
set screws on the Band
11
C
11
oscillator .drive flexible coupler*.
4. Loosen the collet on the Band
11
A
11
oscillator tuning shaft.
5. Loosen the set screw (j) (See Fig. 2 page 9) that fastens the front band svJitch
lever to the coupling rod. @ .
6. Remove the four 4-40 screws @,; that fasten the dial housing to the
front oscillator mounting plate* ;3·, and remove the dial housing.
7.
Remove the two screws that fas ten the back end of the Band
11
C
11
osci 11 a tor
to the rear sup port bracket (6--;.
,_...,
8. Observe the orientation of the front mounting plate (3J , and remove two
screws, one flat head and one pan head, that fasten the Band
11
C
11
oscillator to the front mounting bracket.
9. Remove the two socket head screws ~6) that fasten the front mounting
Plate to the Band
11
A
11
oscillator, and remove the Band
11
C
11
oscillator,
and the front mounting plate*.
C. TO INSTALL NEW BAND
11
C
11
OSCILLATOR
( )
1.
Temporarik remove the two screws r28J that fas ten the band switch
bracket ® to the Band
11
B
11
osci l'lftor rear support. ®
Fas ten the Band
11
C
11
osci 11 a tor rear support angle bracket @ over the
band switch
bracket with the hardware just removed.
( ) 2. Fasten the
new front oscillator mountil']g plate m to the Band
11
A
11
oscillator using the hardware removed in Step B..:-g:
( ) 3. Reins tall the di al housing by ins tall i ng the two top screws that fas ten
the di al housing to the
new front oscil 1a tor mounting pl ate. DO NOT
TIGHTEN COLLET ON BAND A OSCILLATOR.
( ) 4. Fasten the Band C oscillator front angle bracket to the bottom holes
of the dial housing and replace the bottom left mounting screw with
the button head screw.
~
* Discard. Part will not be used in new assembly.
Page 4 of 9 050-0692- O2

INSTRUCTIONS : (ContI d)
( )
( )
( )
5. Slide the new shaft coupler @ over the Band A" oscillator dial
assembly drive shaft, put the extension shaft ~ into the shaft
coupler. @
6. Install half of the new flexible coupler @. on the shaft extension
@ and the other half on the Band "C" oscillator drive shaft.
7. Install the Band "C" oscillator* as follows:
* NOTE: Be sure the os ci ll a tor is turned to the high end (fully
clockwise) of the Band.
a)
b)
Align the two halves of the flexible coupler@ and insert the
center part of the flexible coupler.
Fasten the Band "C" oscillator in place with the 4-40 X .250 inch
screws
@·
( ) 8. Reconnect the band switch lever to the coupling rod @ on the dial
housing.
() 9. Align the Band "C" Oscillator as follows:
a. Temporarily reinstall the Tuning knob on the main dial drive shaft
and check for smooth operation of the Tuning knob.
b.
The Band "C" Oscillator rear support is fastened to the back end of
the Band "B" Osei ll a tor by a 1 u• shaped bracket. This bracket allows
mechanical
adjustment in two directions.
c. Side to Side adjustment is accomplished by loosening the set screw,
one on each side, and tightening the set screw on the other side.
D. TO REPLACE DIAL TAPE
( ) 1. Turn the Tuning di al** all the way to the high end, fully clockwise.
( ) 2. Remove the dial window mounting screws and remove the dial window.
( ) 3. Manually run
the dial tape off of the right hand spool, and pull the
tape off of the left hand spool.
( ) 4. Wind the new dial tape so the low end is on the outside. Thread
the dial tape onto the left hand spool and wind all of the tape on.
Then slip the high end over the right hand spool and turn until the
high end of the dial is in the center of the window, and reinstall
the di a1 wi n dow.
**The collet on the Band "A" Oscillator and the set screws in the Band "C"
Oscillator shaft coupler should both be loose.
Page 5 of 9 050-0692- 02

-------------------~--------- -----------
INSTRUCTIONS: (Cont
1
d)
E. TO REPLACE CONNECTOR CIRCUIT BOARD
( ) l. Unsolder all of the wires from the pin connector circuit board on the
Phase lock chassis and replace the connector circuit board with the new
Connector circuit board, from the kit, and wire as follows:
--
Pin
Wire Color Pin
Wire Color ----·
A white
and #22 bare
E*
white-black
wire to pin B F white-brown-red
B Shield for pins G white-brown-green
C &D H white-black-brown
c Red
I* white-vio1
et
D Black
J*
white-blue
F. TO REPLACE OSCILLATOR CONNECTOR BOARD. SEE FIG. 1
( )
1. Unsolder all of the wires from the oscillator connector circuit board.
( )
2. Remove the oscillator circuit board mounting screws and replace the
circuit board with the new board and wire as follows:
( ) 3. Solder the White-red wire
(See Ftg. 1) to the -20VDC termina1 on the
Band
11
C
11
osci1 lator.
( ) 4. Solder the white wire from the ground connection on the Band
11
C
11
oscillator to the grounded** side of the Band
11
B
11
filament.
( ) 5. Solder the white-black wire
from the AFC terminal on the Band
1C1
oscillator to the AFC terminal on the Band
1B1
oscillator.
( ) 6. Connect the remaining wires as shown in the drawing.
FIGURE 1.
WHT-BLK--
* The white-black, white-violet, and white-blue wires will be connected in
step G4-6.
** Terminal toward the back. CHECK WITH OHMETER TO BE SURE.
Page 6 of 9 050-0692-02

INSTRUCTIONS: (Cont'd)
G. TO REINSTALL OSCILLATOR ASSEMBLY
( ) 1. Reinstall the oscillator assembly in the instrument using the hard-
ware removed in Step A-10. Two 6-32 screws in the back end and two
6-32 nuts in the front.
( ) 2. Reinstall the 4-40 screw below the tuning shaft that fastens the
dial housing to the
front panel.
( )
3. Reinstall the Tuning knob and the Band Switch Lever, and switch the
Band Switch to check for proper knob position. The knob position
can be adjusted by moving the switch lever on the coupling rod.
Reconnect wires to connector block
on chassis as follows:
( ) 4. White-blue wire to
Pin J.
( ) 5. White-violet wire to Pin I.
( ) 6. White-black wire to Pin E.
Connect wires to oscillator connector board terminals from top to
bottom
as follows:
( )
7. White wire (ground).
( ) 8. White-black-brown wire.
( )
9. White-brown-green wire.
( ) 10. White-black wire.
( ) 11. Reconnect the sub-miniature coaxes
removed in Step A-9 and connect the
coax from the LO output on the Band
11
C
11
oscillator to J45 on the IF
Multiplexer and connect the Phase Lock connector on the Band
11
C
11
osc-
illator to Jll40 on the Phase Lock Assembly.
( ) 12. Dress the three wire ribbon cable from the oscillator circuit board
back and through the chassis. Solder the white-orange wire to the
ground solder lug on the power supply chassis near C954.
The connector will be connected to the new -20 Volt Power Supply in
Step H-8.
Page 7 of 9 050-0692-02

INSTRUCTIONS: (Cont'd)
H. INSTALL THE -20VOLT POWER SUPPLY AS FOLLOWS:
( ) 1. Place the instrument on the workbench bottom side up, release the lock
on the IF Control Circuit Board and swing it open to gain access to
the
Power Supply Circuit Board.
{ ) 2. Add the #6 solder lug to the bottom mounting screw of the RFI filter.
Solder the white-brown wire, from the kit, to this solder lug. Other
end will be connected in Step H-7.
( ) 3. Remove the two mounting screws from the Power Supply Circuit Board
near the RFI filter.
( ) 4. Disconnect the white-black-yellow wire from Pin AA on the Power Supply
Circuit Board. Connect the 2 3/4 inch white-black-yellow wire from
the kit to Pin AA. These b-10 wires wi 11 connect to the new circuit
board in Step H-6.
( ) 5. Mount the -20Volt Power Supply Circuit Board above the Power Supply
Circuit Board on the .781 inch spacers and fasten in place with the
1.250 inch 4-40 screws in the holes vacated in Step D-1.
( ) 6. Connect the two white-black-yellow wires mentioned in Step H-4 to
Pin A and Pin B of the -20Volt Power Supply.
( )
7. Connect the white-brown wire installed in Step H-2 to Pin Cof the
-20Volt Power Supply.
( ) 8.
Connect the two wire ribbon connector from the oscillator connector
board to
P920 on the -20Volt circuit board.
( ) Refer to the Calibration Procedure in your
Instruct~on Manual and
the supplemental Calibration procedure in the Instruction Manual
Modificat.ion Insert at the back of thjs kit and recalibrate as
required.
( )
For future reference fasten the Modification Insert in your Instruction
Manual.
Page 8 Of 9 050-0692-02

ITEM
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
PART NUMBER
331-0176-03
175-1529-00
386-1139-00
119-0108-01
407-0295-00
407-0294-00
213-0075-00
260-0821-00
337-0880-00
119-0063-01
175-1530-00
407-1545-00
384-0425-00
211-0062-00
211-0012-00
210-0004-00
211-0504-00
407-1546-00
210-0006-00
211-0098-00
213-0004-00
210-0405-00
210-0053-00
131-0391-00
176-0124-00
211-0564-00
175-1531-00
211-0008-00
670-0523-08
211-0116-00
376-0029-00
376-0099-00
384 .. 1265-00
QUANTITY
1
1
1
1
1
1
4
1
1
1
1
1
1
1
3
8
2
1
6
1
2
3
3
4
As Req.
2
1
4
1
2
1
1
1
DESCRIPTION
Dial Assembly Tape
Cable Assembly, Elec (LO)
Plate Mounting Oscillator
Oscillator Assembly, RF
Support, Oscillator
Bracket, Oscillator
Screw, 4-40 x .094 Socket Head
Switch Lever
Shield Rotary Switch
Oscillator, Cavity
Cable Assembly, Elec (Lock)
Bracket, Angle (Oscillator Front)
Rod, Coupling
Screw, 2-56 x .312 PH
Screw, 4-40 x .375 PH
Lockwasher, #4 Internal
Screw, 6-32 x 250
Bracket, Angle (Oscillator Rear)
Lockwasher, #6 Internal
Screw, 4-40 x .375 Button Head
Screw, 6-32 x .188 Socket Head Set
Hex Nut, 2-56 x .188.
Lockwasher, #2 Split
Connector, coax
Wire, .0508 #16 AWG Dia, Tinned CU
Screw, 6-32 x .375 Socket Head
Cable, Assembly, Elec.
Screw, 4-40 x .250 PH
Oscillator Connector Circuit Board
Screw, 4-40 x .312 Assembly washer
Coupler
Coupler
Shaft
I
I
II
r.;:vL.o...icr u~. CN-,..)
~·~
FIG. 1A
Fig. 2
050-0692-01
Page 9 of 9