Tektronix 7L5 User manual

Tektronix.
COMMITTED TO EXCELLENCE
PLEASE CHECK FOR CHANGE INFORMATION
AT THE REAR OF THIS MANUAL.
7L5
SPECTRUM ANALYZER
OPTIONS
INSTRUCTION MANUAL
Tektronix, Inc.
P.O. Box 500
Beaverton, Oregon 97077 Serial Number
070-2155-03 / FIRST PRINTING OCT 1976
Product
Group
26
Revised
JAN
1982

Copyright © 1976, 1977, 1978 Tektronix, Inc. All rights
reserved. Contents of this publication may not be
reproduced in any form without the written permission of
Tektronix, Inc.
Products of Tektronix, Inc. and its subsidiaries are
covered by U.S. and foreign patents and/or pending
patents.
TEKTRONIX, TEK, SCOPE-MOBILE, and el are
registered trademarks of Tektronix, Inc. TELEQUIP-
MENT is a registered trademark of Tektronix U.K.
Limited.
Printed in U.S.A. Specification and price change
privileges are reserved.

—
7L5 Options
GENERAL INFORMATION
INTRODUCTION
This manual contains documentation for the 7L5
Spectrum Analyzer Options. Each is a complete and
separate section or supplement to the manual. Changes
and corrective information are added, at the back of the
manual. This information is incorporated into the respec-
tive manual text and diagrams when the option section is
reprinted. History information is included with the up-
dated data. Original pages are identified by the symbol @,
revised pages by a revision date on the lower inside corner
of the page. These options add an assembly, with its part
number; to the 7L5 instrument. The suffix portion of the
part number signifies updating process of the assembly.
Up-dated manual supplements may contain information
that is not applicable to your instrument; however as
previously stated, the manual does contain history infor-
mation.
Depending on the production model of the 7L5, it may
be impractical to field install some option assemblies.
Contact your local Tektronix Field Office or representative
for information.
INSTALLATION AND REPACKAGING
Initial Inspection
The instrument was inspected both mechanically and
electrically before shipment. It should be free of mars or
scratches and. electrically meet or exceed all
specifications. To confirm this, inspect the instrument for
physical damage that may have occurred in transit and
test the electrical performance by following the Operating
Instructions and Performance Check Procedure in the
section applicable to the Option. If there is damage, or if
the instrument does not perform, contact your local
Tektronix Field Office or representative.
Installation
These options are normally shipped attached to the 7L5
and ready to plug into the 7000-Series mainframe. If the
option is shipped as a field modification kit, instructions
on how itis installed to the 7L5 will be included with the kit.
After installation, plug the 7L5 with option into a 7000-
Series mainframe, and proceed as directed in the
’ Operations section of this manual. (Both Options 25 and
21 require a mainframe with readout.)
Repackaging for Shipment
If a Tektronix instrument is to be shipped to a Tektronix
Service Center for service or replacement, attach a tag
showing, owner (with address) and the name of an
individual at your firm that can be contacted. Include
complete instrument serial number and a description of
the service required.
Save for re-use the shipping container your instrument
was shippedin. If the original packaging is not available,
or is unfit for use, repackage as follows:
1. Obtain a shipping container made of heavy cor-
rugated cardboard or wood with inside dimensions of no
less than six inches more than the instrument dimensions;
this will allow room for cushioning. Refer to Table 1 for
carton test strength requirements.
2. Wrap the instrument in heavy paper or polyethylene
sheeting. Protect the front panel with urethane foam or
cardboard strips.
3. Cushion the instrument on all sides by tightly
packing dunnage or urethane foam between the carton
and the instrument allowing three inches on all sides.
4. Seal the carton with shipping tape or an industrial
stapler.
TABLE 1
Gross Weight (Ib) Carton Test Strength (Ib)
10-30 275
30-100 375
120-140 500
140-160 600
If you have any questions, contact your local Tektronix
Field Office or representative.

—_
—
am
7L5 Option 21
7L5 OPTION 21
Log Sweep
General
Information
IRIG
PROPORTIONAL
BANDWIDTH
SUBCARRIER
CHANNELS
The
7L5
Option
21
provides
the
additional
feature
of
an
LOWER
|
CENTER
|
UPPER
|
BAND
IRIG
logarithmic
frequency
span
(250
Hz
to
222
kHz)
LIMIT
FREQ
LIMIT
WIDTH
display.
Because
the
display
is
generated
from
three
CHANNEL
;
(CPS)
(CPS) (CPS)
(CPS)
sweeps,
covering
a
decade
of
frequency
each,
digital
storage
memory
operation
is
used.
Resolution
and
sweep
:
ere
ay
ane
“
time
are
automatically
controlled
to
provide
an
amplitude
é
518
560
602
84
calibrated
display
for
the
data
acquisition
time.
Signal
3
675
730 785
110
acquisition
time
for
one
display
is
no
more
than
2.5
4
888
960
1,032
144
seconds.
A
Sweep
Inhibit
feature
will
store
and
display
any
5
1,202
1,300
1,398
196
full
span
log
display
until
SWP
INHIBIT
is
switched
off.
6
1,572
1,700
1,828
256
This
is
equivalent
to
single
sweep
operation.
f
2,127
2,300 2,473
346
8
2,775 3,000
D200
450
)
3,607
3,900 4,193
586
10 4,995
5,400
5,805
810
ae ak
6,799 7,350 7,901 1,102
9,712 10,500 11,288 1,576
13,412 14,500 15,588 2,176
20,350 22,000 23,650 3,300
27,750 30,000 32,250 4,500
37,000 40,000 43,000 6,000
48,560 52,500 56,440 7,880
64,750 70,000 75,250 10,500
86,025 93,000 99,975 13,950
114,700 124,000 133,300 18,600
152,625 165,000 177,375 24,750
@ An IRIG graticule overlay is provided as a standard
accessory. The graticule can be inserted over the face of
the crt behind the crt bezel. The following table lists
proportional bandwidth subcarrier channels.
Sees
Ua,
eb
bhwNnh
NSD
ed
ee
-00O
0
NWN
L@
NOILdO
@
Option
21
Page
i

SECTION 1
SECTION 2
TABLE OF CONTENTS
SPECIFICATIONS
Electrical Characteristics
Environmental Characteristics
Accessories
OPERATING AND PERFORMANCE CHECK INSTRUCTIONS
Introduction
Function of Controls and Connectors
Operational Check
1. Preliminary Preparation
2. Check Frequency Range and Display Flatness
3. Verify Sweep Inhibit Operation
7L5 Option 21
Page
—_
oot
'
2
2-1
THE FOLLOWING SERVICING INSTRUCTIONS ARE FOR USE BY QUALIFIED PERSONNEL ONLY.
TO AVOID PERSONAL INJURY, DO NOT PERFORM ANY SERVICING OTHER THAN THAT
CONTAINED IN OPERATING INSTRUCTIONS UNLESS YOU ARE QUALIFIED TO DO SO.
SECTION 3
SECTION 4
SECTION 5
SECTION 6
SECTION 7
SECTION 8
CALIBRATION
Equipment Required
1. Preliminary Preparation
2. Calibrate the Sweep Span to 10 kHz
3. Calibrate the Log Sweep
4. Calibrate Resolution Bandwidth
CIRCUIT DESCRIPTION
General
Detailed Description
MAINTENANCE INSTRUCTIONS
Introduction
Preparing the Instrument for Service
Replacing the Assembly
REPLACEABLE ELECTRICAL PARTS
DIAGRAMS
REPLACEABLE MECHANICAL PARTS
CHANGE INFORMATION
3-1
4-1
Option 21 Page ii

Se
-
4)
,
|
—)J
—)
__]
Fig. Option 21. 1-1. 7L5 Option 21 (Log Sweep).
7L5 Option 21 REV. A FEB 1978
—J
—J
—_J
__}

Section 1—7L5 Option 21
SPECIFICATIONS
ELECTRICAL CHARACTERISTICS
The following characteristics and features apply to the
Option 21 (Log Display) portion of the 7L5 Option 21
Spectrum Analyzer. 7L5 characteristics are not affected
by this option. These characteristics are applicable over
the environmental specifications criteria for the 7000-
Series mainframe.
Frequency Range (Log Display): 250 Hz to 222.25 kHz,
in increments of; 250 Hz—2.25 kHz, 2.25 kHz— 22.25 kHz,
and 22.25 kHz—222.25 kHz.
Signal aberration (spread or overlap) generated at the
crossover points (i.e. 2.25 kHz, 22.25 kHz, etc.) shall
not exceed 0.5 minor division.
Display Flatness: +0.5 dB, —1.5dB from 300 Hz to
180 kHz.
Acquisition Time/Full Log Display: Not more than 2.5
seconds. When 220 kHz IRIG (Log Display) is on, all
except the REFERENCE LEVEL, Display Mode, and
MAX HOLD selectors on the 7L5 are disabled. DOT
FREQUENCY is not operational. When 220 kHz IRIG
(Log Display) is off, the 7L5 operation is normal. When
SWP_ INHIBIT is enabled (illuminated) with Log
Display, sweep operation is similar to single sweep
mode. Data acquired during full log span period, is
stored and displayed until the sweep is retriggered by
switching SWP INHIBIT off.
ENVIRONMENTAL CHARACTERISTICS
As previously described, the instrument will meet the
electrical characteristics over the environmental limits of
the 7000-Series mainframe. Complete details on test
procedure are described in the mainframe manual.
Operating and Storage Requirements
Operating Temperature Range: 0°C to +55°C.
Storage Temperature Range: —54°C to +75°C.
ACCESSORIES
Standard Accessories
Manual, Instruction
IRIG Log Graticule for 7L5 Option 21 331-0421-00
Option 21 Page 1-1

a)
J)
—_]
4

Section 2—7L5 Option 21
~ _ OPERATING AND PERFORMANCE CHECK
INSTRUCTIONS
Introduction
This section describes the function of front panel
selectors and provides an operational or performance
check procedure. This operational check can be used to
verify that the instrument is operating satisfactory and will
serve as a guide for incoming inspection.
The Option 21 assembly provides a logarithmic display
over the Inter Range Instrumentation Group (IRIG) re-
quirements for the frequency range 250 Hz to 222.25 kHz.
Log display is front panel selectable. Normal linear
operation of the 7L5 is unchanged when the Option 21 is
off. A IRIG graticule overlay, with subcarrier channels
noted, is a standard accessory.
Function of the Panel Selectors
Two momentary pushbutton switches illuminate when
their function is asserted.
220 kHz IRIG: Switches the spectrum analyzer span toa
300
Hz to 180 kHz log display. When on, all except the 7L5
Reference Level, Display Mode, (Log-Lin) and Max Hold
selectors are disabled. Sweep consists of three segments
with breakpoints at 2.25 kHz and 22.25 kHz. When off, the
7L5 operation is normal.
SWP INHIBIT: When activated (illuminated) the instru-
ment will complete a full log display. The data acquired
will remain stored and displayed until the switch is pushed
again to change the state to off.
OPERATIONAL CHECK
This check will verify that the Option 21 assembly
meets the electrical charactersitics specified.
Equipment Required or Recommended
Test equipment specifications are the minimum re-
quired for these checks.
1. Two Sine Wave Signal Generators: Frequency
range 250 Hz to 250 kHz. Variable output level. Output
impedance 50 9 or 600 Q. TEKTRONIX SG 502 Oscillator
of the TM 500 Series Test and Measurement instruments.
2. An "L"-Series plug-in module that matches the
source impedance of the signal generator.
3. One, BNC "T" Adapter: Tektronix Part No. 103-
0030-00.
1. Preliminary Preparation
a. Plug the 7L5 Option 21 into a 7000-Series main-
frame with readout. Install an "L" series plug-in module
into the 7L5. (Plug-in module input impedance should be
the same as the signal generator output impedance.)
b. Turn the mainframe power on and allow a few
minutes (about 5) warmup.
c. With the Log Display (220 kHz IRIG) off, calibrate
the 7L5 span and position the display as described in the
7L5 Operating instructions.
2. Check Frequency Range and Display Flatness
a. Apply the output from two signal generators
through a BNC "T" connector and coaxial cable to the
Input of the 7L5 plug-in module.
b. Set the frequency of one generator to 300 Hz and
the frequency of the other generator to 180 kHz. Adjust
the output level of both generators to 0 dBm.
c. Switch the 7L5 Display Mode to 10 dB/DIV and the
220 kHz IRIG Log Display on.
d. Check—the display for the 300 Hz and 180 kHz
signals within +0.5, —1.5 dB, of 0 dBm. Note that only the
Display Mode and Reference Level selectors of the 7L5 are
functional when the Log Display is active.
3. Verify Sweep Inhibit Operation
a. Activate the sweep inhibit mode by pressing the
SWP INHIBIT pushbutton.
b. Verify that the sweep is locked out, at the comple-
tion of one sweep by changing the Display Mode to
2 dB/DIV of LIN and observe that the display does not
change.
Option 21 Page 2-1

Section 3—7L5 Option 21
WARNING
THE FOLLOWING SERVICING INSTRUCTIONS ARE
FOR USE BY QUALIFIED PERSONNEL ONLY. TO
AVOID PERSONAL INJURY, DO NOT PERFORM ANY
SERVICING OTHER THAN THAT CONTAINED IN
OPERATING INSTRUCTIONS UNLESS YOU ARE
QUALIFIED TO DO SO.
CALIBRATION PROCEDURE
The following procedures describe the steps necessary
to re-calibrate the Option 21 (Log Sweep) assembly. When
calibrated, the instrument will operate within the
characteristics specified in the Specifications section.
History Information
The instrument and manual are periodically evaluated
and updated. If modifications require changes to the
calibration procedure, history information applicable to
earlier instruments is included.
Equipment Required
Equipment for calibration includes the equipment
listed for the Performance Check plus the following
additional equipment.
1. Oscilloscope: Vertical sensitivity 1 V/Div, sweep
rate 1s/Div. Tektronix 5000, 7000, or 400 series with
appropriate time domain vertical and horizontal plug-in
units.
2. Three plug-in extenders: Tektronix Part No. 067-
0616-00.
3. Tuning screwdriver: 1/8 inch blade.
1. Preliminary Preparation
NOTE
The performance of the 7L5 must be checked and
verified before calibrating the Option assembly. To
gain access to the 7L5 for service and calibration,
refer to the Maintenance Instructions.
Calibrate the instrument within its ambient
Operating temperature range. Allow a warmup
period (with power on) of at least 10 minutes before
making any calibration adjustments.
a. Turn the mainframe power off. Remove the 7L5
Option 21 plug-in unit from the mainframe plug-in com-
partment.
b. Remove the snap-on sidepanel to expose the circuit
board and its adjustments.
c. Connect the 7L5 Option 21 through flexible plug-in
extenders (Calibration Fixture No. 067-0616-00) to the
mainframe interface connectors, or, plug the 7L5 Option
21 back into the mainframe and remove the side panel of
the mainframe.
d. Switch the power on and after warmup, proceed
with the calibration.
Option 21 Page 3-1

Calibration Procedure—7L5 Option 21
2. Calibrate the 7L5 Sweep Span to 10 kHz
(2.25 kHz to 22.5 kHz)
a. Apply the output of two signal generators througha
BNC "T" connector and coaxial cables to the Inputofa”L”
plug-in module. Termination impedance of the plug-in
module should match the source impedance of the signal
generators.
b. Set the 7L5 controls as follows:
DOT FREQUENCY 2.25 kHz
SPAN/DIV 0
RESOLUTION 30 Hz
Display Mode 10 dB/DIV
TIME/DIV AUTO
Option 21 LOG DISPLAY OFF
c. Set the frequency of one signal generator to the 7L5
dot frequency of 2.25 kHz (maximum response) then
adjust.the generator output for an on-screen amplitude
reference level (i.e., 7 divisions).
d. Change the 7L5 DOT FREQUENCY to 22.25 kHz
then adjust the frequency of the second signal generator
to the 7L5 dot frequency. Again adjust the generator
output level so the 22.25 kHz signal amplitude equals the
2.25 kHz signal.
e. Set the 7L5 controls as follows:
DOT FREQUENCY 2.25 kHz
SPAN/DIV 2 kHz
RESOLUTION COUPLED
Digital Storage Off
f. Calibrate the lower and upper limits of the 7L5 span
to 2.25 kHz with R664 and 22.25 kHz with R665 respec-
tively. Sweep should not overspan or underspan these
limits (see Fig. 3-1).
Option 21 Page 3-2
nos Ab |
Pepi east) yy
tT eae
Boa sia
7
4 Ey it rete)
A. Sweep adjustment location on the 7L5.
| + REF
mil L225KN2
1.2 + -20 |
a 3)
q g
SS
2155-17
B. Typical calibrated 2.25 kHz span.
Fig. Option 21. 3-1. Adjustment location and typical calibrated
display of the 7L5 2.25 kHz to 22.5 kHz span.
NOTE
Refer to the 7L5 Service manual for access instruc-
tion to these adjustments on the Sweep circuit
board.

oo
3. Calibrate the Log Sweep
a. Center the Resolution Gain (R5610) and Resolution
Offset (R5625) adjustments (see Fig. 3-2).
b. With the signal generator frequencies of 2.25 kHz
and 22.25 kHz applied to the 7L5 Input as described in step
2, adjust the Log Gain (R5595) and 22.25 kHz Offset
(R5615) for minimum shift of the two signals as the
analyzer sweeps through these two frequency points. See
Fig. 3-3.
c. Change the signal generator frequencies to 500 Hz
and 111.00 kHz.
d. Adjust the separation of the two signals to eight
divisions with R5645 (Swp Gain), then, adjust R5605 (Swp
Offset) so the two signals are aligned with their respective
IRIG Log graticule markers (500 Hz and 111.00 kHz).
Fig. Option 21. 3-2. Calibration adjustment locations for Option
21.
Calibration Procedure—7L5 Option 21
+ REF
1.4 a ‘A. ae Boye 17
ou Ly a
ee
+4++4+4-++++
A>
o-
L
A. Typical display when log span and 22.5 kHz offset are
incorrect.
MTS aR:
2156.20]
(SERS,
B. Typical calibrated log display with 2.25 kHz and 22.5 kHz
signal applied.
Fig. Option 21. 3-3. Log display calibration, 22.25 kHz.
Option 21 Page 3-3

Calibration Procedure—7L5 Option 21
4. Calibrate Resolution Bandwidth
a. Connect the probe from test oscilloscope to pin 7
of U5605. Set the sweep rate to 500 ms/Div and vertical
sensitivity to 1 V/Div.
b. Adjust the Resolution Gain (R5610) for 4 volt ramp
and Resolution Offset (R5625) so the ramp sweeps from 0
to +4 volts (see Fig. 3-4).
c. Disconnect the test oscilloscope probe.
This completes the calibration of the Option 21 (Log
Sweep) assembly.
Option 21 Page 3-4
12 1 -29)
1.0 tLe =30)
8 fi 40
EEE EEE HEE EEF
:
=
+
Lt
ao | -60
HEHE HH bed
2 t =70
L + L
! 1¥
NI ao oe detRck dat Pi tt Stk J dot Jo cL)
2155-21
Fig. Option 21. 3-4. Composite sweep for log display.

Section 4—7L5 Option 21
CIRCUIT DESCRIPTION
General
The Log Sweep Option provides a log display from
250 Hz to 222.25 kHz, generated by combining three 7L5
sweeps. Each sweep spans a decade in frequency. The
assembly circuits consist of a digital section to program
the 7L5 center frequency, resolution, sweep time, and
frequency span; plus an analog circuit to shape the sweep
and automatically correct the resolution bandwidth and
sweep time as the frequency increases.
During the 7L5 sweep holdoff period, the digital circuit
generates and sends center frequency, frequency span,
resolution, and sweep time data to the 7L5. This data then
programs the 7L5 circuits for the next sweep. When the
7L5 sends Valid (sweep running), the digital circuit is
inhibited and the analog circuit shapes and compresses
the sweep horizontal (from the 7L5) into a logarithmic
sweep. The sweep is then sent to the 7L5 digital storage
circuit. After three sweeps the sweep horizontal out of the
digital storage, is a composite of the three sweeps and the
display is a log span from 250 Hz to 222.25 kHz. Fig 4-1
illustrates the conversion sequence. This display meets
the requirements of the Inter Range Instrumentation
Group (IRIG) within the specified frequency range.
Detailed Description
Valid input from the 7L5 is high during sweep time. It is
inverted by U5455E, differentiated by C5493-R5493, then
diode CR5493 couples the positive pulse portion of the
differentiated signal to the Set input of two flip-flop IC’s
U5466A and U5466B. When U5466B is set, a master
oscillator, consisting of U5455C, U5455B is enabled and
outputs a clock with a frequency of approximately
1.1 kHz.
The positive-going portion of Valid, clocks a modulo-3
counter (U5497A & B). This counter is initially reset to 00
(by the Q output of U5542A) when the Option 21 is
switched on; so the counter is clocked through 0,1,2, for
each series of three Valid input signals.
When the master oscillator is enabled, the 1st clock
pulse
is gated through U5476B and inverted by U5481B to
load the shift register U5505 with a byte of data out of ROM
U5500. The initial address into ROM U5500 is 0000,
derived from the output of the 6-bit counter (U5485A & B)
and the output of the modulo-3 counter (U5497A & B). The
data in the shift register (U5505) is now clocked out online
N as center frequency data and into shift registers U5513,
U5489.
With the 8th clock pulse the A output of U5485B goes to
1 to change the address to ROM U5500 and another byte of
data is loaded into U5505 (8th pulse is gated through
U5476B). The 16th clock changes the B output of U5485B
to 1. This generates a new byte of data out of ROM U5500
and again this is loaded into the shift register U5505. The
high on the B output of U5485B enables gate U5476C so
that the next count to the K input of U5466A goes high. The
17th pulse now clocks the flip-flop, inhibits the gate
U5476D, and terminates the clock to the MOS IC (on line
N) for the 7L5. The 24th pulse changes the output of the 6
bit counter (U5485B) and loads a new byte of datainto the
shift register U5505. The 32nd pulse changes the output of
U5485B to 100 (4) with the high out of C, strobing data in
shift registers U5513 and U5489 to output latches within
the IC. Up to this time, excess data bits where clocked out
of U5489. The 14 bits of data strobed from the two registers
in U5513, U5489 provide a new and different program for
the 7L5 frequency span, resolution, and sweep time.
The high on this line (C output of U5485B) allows the
next clock pulse to clock the flip-flop U5466B and disable
the oscillator. The Option 21 circuit is now ready for the
7L5 sweep to run.
At the end of the next Valid the modulo-3 counter shifts
up one count, the oscillator is enabled, and the process
repeats with a 1 at the A2 input to ROM U5500, U5497A &B
counts 0,1,2, then repeats. The output of this counter is
also applied through R5412 and R5614 to the input of
operational amplifier U5605A so; as the counter cycles,
the input dc level to amplifier U5605A is offset and the
sweep voltages to the amplifier input are stacked for three
" sweeps.
Option 21 Page 4-1

Calibration Procedure—7L5 Option 21
The analog section log shaping circuit consists of two
transistors, within a common package (U5585), and
amplifier U5580A. The base-emitter junction of one tran-
sistor is in the feedback loop of amplifier U5580A. So the
junction characteristics provide the logarithmic gain
characteristics for the amplifier. The other transistor
provides temperature compensation to maintain the
response characteristics as temperature varies. The input
of the amplifier is offset so all sweeps out of the
logarithmic circuit start from a common reference level.
The compressed log sweeps out of buffer amplifier
U5580B are applied to a gain and offset amplifier US605A.
As previously described, the dc level at the input of
U5605A is changed by the digital circuitry to offset each
sweep. The output of U5605A is therefore three log
sweeps with each sweep stacked on the other. Gain and
Offset adjustments, R5595 and R5605, are set so the three
decades of frequency span do not overlap and the total
sweep amplitude covers 250 Hz to 222.25 kHz. The output
of U5605A is then fed through Swp Gain adjustment R5645
to the Horizontal of the 7L5 digital storage.
The three sweeps out of U5605A are also fed to another
operational amplifier with a Gain and Offset adjustment
Option 21 Page 4-2
(R5610 and R5625) to drive the 7L5 resolution filter and
sweep timing circuits. These are adjusted to provide
optimum resolution bandwidth and sweep rate as frequen-
cy increases.
A sweep inhibit circuit, consisting of gates and latches,
allows the 7L5 to make three sweeps for one complete log
display and then inhibit the sweep until the front panel
SWEEP INHIBIT button is pushed again. When SWP
INHIBIT is activated, U5542B is clocked and Q goes low.
When all inputs to gates U5562C and U5572D are low
(after the 3rd sweep) the output of U5572A, and U5572B,
latches low. Q5520 is switched on to generate Sweep
Inhibit so, the 7L5 sweep is locked out until the latch is
again flipped by pushing the SWP INHIBIT button or,
when U5542B is reset at the initial turn on.
Flip-flop U5542A activates the Option 21 circuit so the
display becomes a log display. When Q of U5542A
switches low, the output of tri-state buffers (U5509) are
enabled, the cursor circuit of the 7L5 is disabled so the
signals are peak detected, and the modulo-3 counter
(U5497) is enabled, sweep inhibit flop-flop U5542B is
reset, shift registers U5513, U5489 are enabled, and
U5466A and U5466B are set.

Calibration Procedure—7L5 Option 21
U5455E
OUTPUT
apa
CENTER CENTER CENTER
FREQ FREQ FREQ
| | |
| |
swe
HORIZ l |
|
12.25 kHz |
| 2 kHz/DIV |
.25 kHz | 222.25 kHz
VALID \ | |
SET PULSE
TO U5466B &
U5466A | | | | |
| | l |
Seay |
5466B
| | |
l | | | | |
oureur_t
ULI
LIU
WLU
U5455B | | 32 CYCLES | l 32 PULSES l | 32 PULSES
|
LOG
|
|||
|
|
SWEEP
OUT
OF
|
de
|
|
|
NO
U5605A
|
OFFSET
l PIN 2 |
U5605A | |
dc
| | | OFFSET |
PIN 2
I u5605A_—sid
2155-18
Fig. Option 21. 4-1. Sequence of signals to convert three 7L5 sweeps to one composite log sweep.
@ Option 21 Page 4-3

Section 5—7L5 Option 21
MAINTENANCE INSTRUCTIONS
Introduction
Preventative maintenance, troubleshooting techni-
ques, and corrective maintenance procedures for the 7L5
are applicable for the Option 21 assembly. The following is
additional information pertinent to the Option 21
Assembly.
Preparing the Instrument for Service
1. Turn the mainframe power off. Remove the 7L5
Option 21 from the plug-in compartment.
2. Remove the snap-on side panel to expose the circuit
board.
3. Connect the 7L5 Option 21 through flexible plug-in
extenders (Calibration Fixture No. 067-0616-00) to the
mainframe interface connectors; or, plug the 7L5 Option
21 back in the mainframe and remove the left side panel of
the mainframe.
4. Switch the power on and proceed with calibration or
troubleshooting.
Replacing the Heater on Transistor Q5585
The heater element R5577 is attached to the top of the
transistor with epoxy glue. When the heater is glued to the
case, ensure that the leads of the heater do not touch the
transistor case.
Replacing the Assembly
Refer to the replacement procedure described in the
Maintenance section for the Option 25 assembly.
Option 21 Page 5-1