Tektronix TG501 User manual

Tektronix
INSTRUCTION MANUAL
TG 501
TIME MARK
GENERATOR

lëktronix
COMMITTED TO EXCELLENCE
PLEASE CHECK FOR CHANGE INFORMATION
AT THE REAR OF THIS MAN AL.
TG 501
TIME MARK
GENERATOR
INSTRUCTION MANUAL
Tektronix, Inc.
P.O. Box 500
Beaverton, Oregon 97077
Serial Number -----------------------------------
070-1576-02
Product Group 75
First Printing OCT 1978
Revised FEB 1984

TG 501
TABLE OF CONTENTS
Page
LIST OF ILL STRATIONS ....................................................................................................................... ii
Section 1 Specification ........................................................................................................ 1-1
Section 2 Operating Instructions ....................................................................................... 2-1
WARNING
THE FOLLOWING SERVICE 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 Theory of Operation ........................................................................................... 3-1
Section 4 Caibration Procedure ......................................................................................... 4-1
Performance Check ...................................................................................... 4-1
Adjustment Procedure ................................................................................. 4-5
Section 5 Maintenance ........................................................................................................ 5-1
Section 6 Options ................................................................................................................. 6-1
Section 7 Rep aceab e Eectrica Parts ............................................................................. 7-1
Section 8 Diagrams and I ustrations .................................................................................. 8-1
Section 9 Rep aceab e Mechanica Parts ........................................................................... 9-1
REV D AUG 1980
i

LIST OF ILL STRATIONS
Figure
No. Page
2-1 Pug-in insta ation and remova ................................................................. 2-1
2-2 Contros and Connectors .................................................................................. 2-2
2-3 Timing error of time base .......................................................................... 2-3
2-4 Measuring timing error of time base .......................................................... 2-3
2-5 Markers approximatey at pu se duration and period .............................. 2-4
2-6 Measuring pu se duration .................................................................................. 2-4
2- 7 Measuring pu se period ............................................................................... 2-5
3- 1 Functiona B ock Diagram of schematic diagrams 1 and 2 circuitry ............. 3-3
3-2 Functiona B ock Diagram of schematic diagram 3 circuitry ......................... 3-5
3-3 Functiona B ock Diagram of schematic diagram 4 circuitry ......................... 3-7
3-4 Functiona B ock Diagram of schematic diagram 5 circuitry ......................... 3-9
5-1 Semiconductor device ead configuration found in the TM 500 fami y .... 5-5
5-2 Location of jumpers and integrated circuits required for c ock options ... 5-9
jj @ AUG 1980

TG 501
OPERATORS SAFETY S MMARY
The genera safety information in this part of the summary
is for both operating and servicing personne . Specific
warnings and cautions wi be found throughout the
manua where they appy, but may not appear in this
summary.
power cord into a propery wired receptace before
connecting to the product input or output terminas. A
protective ground connection by way of the grounding
conductor in the power cord is essentia for safe opera 
tion.
Terms In This Manual
CAUTION statements identify conditions or practices that
cou d resut in damage to the equipment or other property.
WARNING statements identify conditions or practices
that cou d resut in persona injury or oss of ife.
Terms As Marked on Equipment
CAUTION indicates a persona injury hazard not im 
mediate y accessib e as one reads the marking, or a
hazard to property inc uding the equipment itse f.
DANGER indicates a persona injury hazard immediate y
accessibe as one reads the marking.
Symbols As Marked on Equipment
DANGER — High vo tage.
Protective ground (earth) termina.
ATTENTION — refer to manua.
Power Source
This product is intended to operate from a power source
that wi not app y more than 250 vo ts rms between the
supp y conductors or between either supp y conductor
and ground. A protective ground connection by way ofthe
grounding conductor in the power cord is essentia for
safe operation.
Grounding the Product
This product is grounded through the grounding conduc 
tor of the power cord. To avoid e ectrica shock, p ug the
Danger Arising From Loss of Ground
Upon oss of the protective-ground connection, a
accessib e conductive parts (inc uding knobs and con 
tros that may appear to be insuating) can render an
e ectric shock.
se the Proper Power Cord
Use on y the power cord and connector specified for your
product.
Use on y a power cord that is in good condition.
Refer cord and connector changes to qua ified service
personne .
se the Proper Fuse
To avoid fire hazard, use on y the fuse of correct type,
vo tage rating and current rating as specified in the parts
ist for your product.
Refer fuse rep acement to qua ified service personne .
Do Not Operate in Explosive Atmospheres
To avoid exp osion, do not operate this product in an
exp osive atmosphere un ess it has been specifica y
certified for such operation.
Do Not Operate Plug-In nit Without Covers
To avoid persona injury, do not operate this product
without covers or pane s insta ed. Do not appy power to
the p ug-in via a p ug-in extender.
@ AUG 1980
iii

TG 501
SERVICE SAFETY S MMARY
FOR QUALIFIED SERVICE PERSONNEL ONLY
Refer als t the preceding Operat rs Safety Summary.
Do Not Service Alone
Do not perform interna service or adjustment of this
product un ess another person capab e of rendering first
aid and resuscitation is present.
se Care When Servicing With Power On
Dangerous votages exist at severa points in this product.
To avoid persona injury, do not touch exposed connec 
tions and components whie power is on.
Disconnect power before removing protective pane s,
so dering, or repacing components.
Power Source
This product is intended to operate from a power source
that wi not appy more than 250 vo ts rms between the
supp y conductors or between either suppy conductor
and ground. A protective ground connection by way of the
grounding conductor in the power cord is essentia for
safe operation.
@ AUG 1980
V

TG 501
TG 501 Time Mark Generator
VI
REV B JAN 1977

Section 1 — TG 501
SPECIFICATION
INTROD CTION
Description
The TG 501 is a genera purpose Time Mark Generator
p ug-in designed to operate in a TM 500 Series Power
Modu e. A Variab e Timing Readout provides a simpe but
accurate means of measuring timing errors over ±7.5%
minimum range. Since many specifications are given in
percentages, the error readout e iminates the need for
computations and, additiona y, essens para ax dis 
crepancies.
waves are seected by se f-cance ing push-buttons when
the rotary switch is in the 521 n position.
A outputs are avai ab e at the front-pane connectors,
or by modification at the interface connector, ocated at
the back of the p ug-in, and the TM 500 Series Power
Modue.
Marker se ection from 5 s through 1 ns in a 1, 2, 5,
sequence is avai ab e. 5 s through 10 ns markers are
se ected by a rotary switch. 5, 2, and 2 ns modified sine
Power supp ies are current imited. The 5 V suppy is
over-votage protected to avoid damage to the integrated
circuits.
Table 1-1
ELECTRICAL CHARACTERISTICS
Characteristics Performance
Requirements Supplemental Information
Markers 5 s through 1 ns in a 1, 2, 5
sequence.
5 s through 10 ns are seected
by a rotary switch. 5 ns, 2 ns,
and 1 ns are push button seected
modified sine waves.
Marker Ampitude >1 V peak on 5 s through 10 ns
markers. >750 mV peak-to-peak into
50  on 5 ns and 2 ns markers.
>200 mV peak-to-peak into 50 
on 1 ns markers.
Trigger Output Signa
Saved to marker output from 5 s
through 100 ns. Remains at 100 ns
for a faster markers.
Ampitude same as marker ampitude.
Interna Reference
Standard Option 01
Crysta Frequency 1 MHz 5 MHz
Stabiity (0°C to +50° C)
after 1/2 hour warm-up
Within 1 part
in 10 5
Within 5 parts
in 10 7
Long-Term Drift
1 part or ess
in 10 5 per
month
1 part or ess
in 10 7 per
month
Setabiity
Adjustabe to
within 1 part
in 10 7
Adjustab e to
within 5 parts
in 10 ’
REV D SEP 1980
1-1

Table 1-1 (cont)
Specification — TG 501
Characteristics Performance Requirement
Supplemental Information
Externa Reference Input
(Avai ab e Ony if U50 and
jumpers are insta ed and U100
is removed)
Lift pin 3 of U350 from socket;
IC and jumpers for 5 or 10 MHz,
1 MHz externa reference requires
jumpers.
Acceptab e Frequencies 1 MHz, 5 MHz, or 10 MHz.
Interna y hard wired so output
frequencies counted down to 1 MHz.
Input Ampitude Must be TTL, compatibe.
Error Readout Range
To ±7.5%.
Timing Error Measurement
Accuracy
Device under test error is
indicated to within one east
significant digit (i.e., to
within one dispayed count).
Exampe; If DUT Timing error reads
3.0% s ow, the absoute accuracy
wi be between 2.9% and 3.1%
s ow.
Table 1-2
ENVIRONMENTAL CHARACTERISTICS
Characteristics Description
Temperature
Meets M L-T-28800B, c ass 5.
Operating
0°C to +50° C
Non-operating -55° C to +75° C
Humidity
95% RH, 0°C to 30°C Exceeds M L-T-28800B, c ass 5.
75% RH, 30°C to 40° C
45% RH, 40° C to 50° C
Atitude Exceeds MIL-T-28800B, c ass 5.
Operating 4.6 Km (15,000 ft)
Non-operating 15 Km (50,000 ft)
Vibration
0.38 mm(0.015 inch peak- Exceeds MIL-T-28800B, c ass 5,
to-peak, 5 Hz to 55 Hz, when insta ed in qua ified
75 minutes. power modu es.
Shock
30 g's (1/2 sine) 11 ms Meets MIL-T-28800B, c ass 5,
duration, 3 shocks in each when insta ed in quaified
direction a ong 3 major axes, power modues.
18 tota shocks.
Bench Handing 12 drops from 45°, 4 inch Meets MIL-T-28800B, c ass 5.
r equiibrium, whichever
occurs first.
Transportation
Qua ified under Nationa Safe Transit Association Preshipment Test
Procedures 1A-B-1 and 1A-B-2.
EMC Within imits of MIL-461A, and F.C.C. Regu ations, Part 15, Subpart J,
Cass A.
E ectrica Discharge
20 kV maximum charge app ied to instrument case.
1-2
REV D AUG 1980

Specification — TG 501
Table 1-3
PHYSICAL CHARACTERISTICS
Characteristics Description
Finish
Anodized a uminum pane and chassis
Net Weight 2 bs., 4 oz. (1 kg.)
Dimensions 2.633 in. (66.8 mm) w
x 11.240 in. (285.3 mm) d
x 4.961 in. (125.9 mm) h
REV C AUG 1980
1-3

Section 2 — TG 501
OPERATING INSTR CTIONS
Installation
The TG 501 is ca ibrated and ready for use when
received. Referring to Fig. 2-1, insta the Generator and
turn on the Power Modue. Check the front-pane of the
Generator to see that the knob skirt is ighted. The TG 501
is designed to operate in any compartment of a TM 500
Series Power Modue. Refer to the Power Modue Instruc 
tion Manua for ine vo tage requirements and Power
Modue operation.
Turn the P wer M dule ff bef re inserting the plug 
in; therwise, damage may ccur t the plug-in
circuitry.
CONTROLS AND CONNECTORS
MARKER Control
Refer to the Contro s and Adjustments page for front 
pane contro s, connectors and indicator descriptions.
Rotary switch se ects individua marker intervas from
5 s to 10 ns. Set to 521n position when using push buttons
for 5 ns, 2 ns and 1 ns. Readout Disp ay is turned off in
521 n position.
Fig. 2-1. Plug-in installation and removal.
REV C AUG 1980
2-1

Operating Instructions — TG 501
Fig. 2-2. Controls and Connectors.
5 ns, 2 ns AND
1 ns P SHB TTON
( 2 ) Se f-cance ing pushbuttons se ect modified sine waves
for 5, 2, and 1 ns when MARKER contro is in 521 n
position. 1 ns marker has a separate output connector.
These aare not variabe.
TRIGGER O T Connector
( 3) Provides trigger pu ses s aved to Marker Output from
5 s through 100 ns. Remains at 100 ns for a faster
markers. Pu se ampitude is ≥1 V into 50 .
1 ns ONLY Connector
( 4) Provides ≥ 0.5 V peak-to-peak amp itude into 50  of
1 ns modified sine wave seected by the 1 ns push button
when MARKER Contro is in 521n position.
MARKER O T Connector
( 5 ) Provides positive markers of ≥ 1 V peak ampitude into
50  for 5 s through 10 ns se ected by MARKER Contro
rotary switch. Provides markers of ≥ 1 V peak-to-peak
ampitude into 50  for 5 ns and 2 ns modified sine waves,
se ected by se f-cance ing push buttons when MARKER
Contro is in 521n position.
VARIABLE TIMING Control
( 6) C oncentric with MARKER Contro switch. Markers are
ca ibrated when center button is pushed in a owing
se ection as indicated by the ighted knob skirt. When
center button is out, output timing is fast or s ow by the
percentage indicated on the Readout Disp ay.
FAST-SLOW Indicators
(7) Light when variabe timing contro is used. 'Fast' ights
when timing is faster than the standard indicated by
ighted knob skirt. 'Sow' ights when timing is s ower.
Percentage faster or s ower is read from VARIABLE
TIMING Readout.
VARIABLE TIMING Readout
(8) Indicates timing variation from standard timing. First
digit is in percent units, second indicates one-tenth
percent units.
OPERATING MODES
Calibrated Mode
When the center-button of the VARIABLE TIMING
Contro is pushed in, the MARKER Contro se ects
ca ibrated marker intervas from 5 s to 10 ns, indicated by
the ighted knob skirt. To se ect 5, 2, or 1 ns modified sine
wave markers, set the MARKER Contro to 521 n position
and press the desired pushbutton.
Variable Timing Mode
When the center button of the VARIABLE TIMING
Contro is out, output timing is faster or s ower than the
ca ibrated marker to the percentage indicated by the
VARIABLE TIMING READOUT Dispay and the FAST-
SLOW Indicator ights. 5, 2, and 1 ns push-button con 
tro ed modified sine waves are not variab e and the
Readout Disp ay is turned off when the MARKER Contro
is in the 521n position.
Readout Display Test
To check the operation of the disp ay LED's (Light 
Emitting Diodes), press the center button of the
VARIABLE TIMING Contro (push in firmy). A LED
segments shoud ight, dispaying 8.8 in the Readout.
2-2
REV C AUG 1980

Operating Instructions — TG 501
TYPICAL APPLICATIONS
The TG 501 can be used for many app ications not
described in the manua . Use the fo owing exampes to
become famiiar with the TG 501 ’ s VARIABLE TIMING
READOUT. Contact your Tektronix Fied Office or
representative for making specific measurements with this
instrument.
Time Base Measurements
To accurate y determi ne the timing error of a time base:
1. Connect the MARKER OUT of the TG 501 to the
Vertica Input of the osci oscope. Usea 50  coaxia cab e
terminated into 50 .
2. Connect the TRIGGER OUT of the TG 501 to the
Externa Trigger Input of the time base. Use a 50  coaxia
cab e terminated into 50 .
Make first time
marker coincide
with first grati 
cule line.
Fig. 2-3. Timing error of time base.
1576-04
3. Se ect externa trigger source on the time base.
4. Seect, for examp e, the 1 µs sweep rate of the time
base.
5 . Set the MARKER Contro rotary switch of TG 501 to
1 µs.
6. Make sure the center button of VARIABLE TIMING
Contro , concentric with the MARKER Contro , is out
(Variab e Timing Mode).
7. Use the Horizonta Position contro of the time base
to make the first time mark coincide with the first graticu e
ine on the osci oscope. See Fig. 2-3.
8. Rotate the VARIABLE TIMING knob unti a time
markers coincide with graticu e ines on the osci oscope,
as shown in Fig. 2-4,
Rotate VARIABLE TIMING
knob until all markers coincide
with graticule lines.
1576-05
9, Either the FAST or SLOW Indicator wi ight
showing whether the time base is faster or s ower than the
ca ibrated markers of the TG 501. Read the percentage of
error from the VARIABLE TIMING READOUT Dispay .
Pulse Generator Measurements
To accurate y determine pu se duration or period of a
Puse Generator:
1. A dua -trace osci oscope is required. Se ect a ter 
nate mode.
Fig. 2-4. Measuring timing error of time base.
2. Connect the MARKER OUT of the TG 501 to one
channe of the dua -trace osci oscope. Use a 50  coaxia
cab e terminated in 50 .
3. Connect the Output of the pu se generator to the
other channe of the dua -trace, using a 50  coaxia cab e
terminated in 50 .
REV E AUG 1980
2-3

Operating Instructions — TG 501
Align first time marker
with beginning of Pulse
Waveform.
One cycle of a pulse in
10 divisions of the grati 
cule.
Time marker at Pulse Dura 
tion. (approximate)
Time marker at Pulse
period, (approximate)
Peaks of time markers at
50% Amplitude of pulse.
1576-06
Fig. 2-5. Markers approximately at pulse duration and period.
4. Set the time/div switch to disp ay 1 cyc e of a pu se
in 10 divisions of the graticu e on the osci oscope, as
indicated in Fig. 2-5.
11. Read the VARIABLE TIMING READOUT Disp ay
and check the FAST-SLOW Indicators as described in
step 9 to find the percentage of error from standard timing.
5. Use the MARKER Contro switch of the TG 501 to
dispay one time marker approximatey at pu se duration
and one at pu se period. A ign the first time marker with the
beginning of pu se wave-form. See Fig. 2-5.
6. Seect Variab e Timing Mode on the TG 501
(VARIABLE TIMING Contro center button out).
7. Use the Vertica Position contro of the osci oscope
to set the peaks of the time markers at 50% ampitude of
the pu se shown tn Fig. 2-5.
8. To check pu se duration, rotate the VARIABLE
TIMING knob unti time marks coincide with pu se
duration, as shown in Fig. 2-6.
9. Either the FAST or SLOW Indicator wi ight,
showing whether the pu se duration of the pu se generator
is faster or s ower than the ca ibrated time mark of the
TG 501. Read the percentage of error from the VARIABLE
TIMING READOUT Disp ay.
10. To check pu se period, rotate the VARIABLE
TIMING knob unti time marks coincide with pu se period.
See Fig. 2-7.
Rotate VARIABLE TIMING
knob until time marker coincides
with pulse duration. 1576-07
Fig. 2-6. Measuring pulse duration.
2-4
REV H DEC 1980

Operating Instructions — TG 501
Rotate VARIABLE TIMING
knob until time marker coincides
with pulse period.
1576-08
Fig. 2-7. Measuring pulse period.
Save and re-use the package in which your instrument
was shipped. If the origina package is unfit for use or not
avai ab e, repackage the instrument as fo ows:
1. Obtain a carton of corrugated cardboard having
inside dimensions of no ess than six inches more than the
instrument dimensions; this wi a ow for cushioning.
Refer to the fo owing tabe for carton test strength
requirements.
2. Surround the instrument with po yethy ene
sheeting to protect the finish of the instrument.
3. Cushion the instrument on a sides by tighty
packing dunnage or urethane foam between carton and
instrument, a owing three inches on a sides.
4. Sea carton with shipping tape or industria stap er.
REPACKAGING FOR SHIPMENT
If the Tektronix instrument is to be shipped to a
Tektronix Service Center for service or repair, attach a tag
showing: owner (with address) and the name of an
individua at your firm that can be contacted, compete
instrument seria number and a description of the service
required.
SHIPPING CARTON TEST STRENGTH
Gross Weight (lb) Carton Test Strength (lb)
1-10 200
10-30
30-120
120-140
140-160
275
375
500
600
REV G DEC 1980
2-5

Section 3 — TG 501
THEORY OF OPERATION
DIAGRAMS 1 & 2
1 MHz Crystal Reference and Enable Gate
The reference frequency is supp ied by the 1 MHz
crysta reference circuitry of Y100, U1 00 and U350A. The
output of the crysta reference circuit is suppied to pin 12
of U110D, which is part of the enab e gate circuit. The
enabe gate circuit, which determines whether the 1 MHz
crysta reference or the 1 MHz variab e c ock is connected
to the phase ock oop, is composed of U110A, U110B,
U110D, and U115D. When the VARIABLE TIMING (OUT)
knob is pushed in and ocked, a ow is on pin 11 of U110D,
a owing the crysta reference osci ator to be avai ab e at
pin 13 of U110D. A ow is a so created at pins 12 and 13 of
U115D, resuting in a high at pin 11 of U115D and at pin 3 of
U110A. The high at pin 3 of U110A causes a ow at pin 5 of
U110B, which a ows U110B to pass the crysta reference
osci ator signa to pin 1 of U230A.
100 MHz Voltage Controlled Oscillator and Dividers
The vo tage contro ed osci ator (VCO) is composed of
an astabe mu tivibrator (Q280-Q285-Q290), an etched
capacitor, and Q272, which supp ies the charge current
for the etched circuit board capacitor. U290D acts as a
buffer for the VCO. The NOR output of U290D is
connected to the Divide-By-Five Counter. The ÷ 5 counter
contains U310A, U310B, and U315A. The output of the ÷ 5
counter is trans ated from ECL into TTL ogic eve s by
Q330, then supp ied to ÷ 2 counter U320.
The input signa to the oop ampifier/fiter is amp ified
and inverted by operationa ampifier U250. The output of
U250 is kept from changing rapid y by C250 and C251.
VR250 eve -shifts the output of U250 to a eve that can be
used to contro the current fow through Q272.
Frequency Control of the 100 MHz Oscillator
Assume that the frequency has been correct up to this
cyc e, and that pins 9 and 12 of U230 are ow. When the
100 MHz VCO frequency is s ower than 100 MHz the
negative edge to the phase comparator wi togge U230A
first. This resu ts in a high at pins 8 and 12 of U230 and a
more negative vo tage at the output of U250. This more
negative vo tage causes Q272 to conduct harder, which
a ows the etched circuit board capacitor to charge more
quick y, thus increasing the osci ator frequency.
Again assume that the frequency has been correct up to
this cyce, but this time the VCO is faster than 100 MHz.
The negative edge of the next cyce wi togge U230B first,
resuting in a ow at pins 8 and 12 of U230. This in turn
causes a more positive vo tage at the output of U250,
which reduces the conduction to Q272. The etched circuit
board capacitor now requires onger to charge since its
avai ab e charging current has been reduced by Q272, and
the frequency is decreased.
The output of ÷ 2 counter U320 is supp ied to the input
of U325. The output, pin 11 of U325 is appied to another
÷ 2 counter (U225 pin 12). The Q output of U225 is
supp ied to pin 5 of U230B.
U230A pin 1 receives 1 MHz from either the crysta
reference or the variab e c ock. U230B pin 5 receives the
counted down ( ÷1 00) 100 MHz signa from the VCO. Pins
9 and 12 of U230 go high if the negative edges of the input
signas coincide; this occurs when the 100 MHz VCO is
operating on frequency. The high inputs to U235A
produce a ow output that c ears U230A and U230B. The
transition to a ow that occurs at pin 12 of U230A is
integrated by R231 and C231; the transition to a high eve
that occurs at pin 8 of U230B is integrated by R239 and
C239. The two integrated output eve s are summed by
R234and R239. This summation is then fed to the negative
input of the oop amp ifier/fi ter.
Out-of-Lock Detector
Ground fr m the cam switch for a the marker output
enab e ogic gates is via Q270. If the 100 MHz VCO is
running s ow (out of specifications), the vo tage at the
output of the oop ampifier/fiter operationa ampifier
Q250 wi be ow. This ow vo tage wi turn on Q255 and
Q260, which wi turn off Q270, stopping the marker
output.
On the other hand, if the 100 MHz VCO is running fast
(out of specifications), the vo tage at the output of U250
wi be high. This high vo tage wi turn off norma y
conducting Q54, which in turn wi turn off Q270, breaking
the ground on the enab e ogic gates. Without ground
there is no marker output.
REV A AUG 1980
3-1

Theory of Operation — TG 501
20 ns and .3 µs Divide-By-Two Counters
The 20 ns ÷ 2 counter contains U315B, U290B and
U290A. The input to the counter is the output of the 100
MHz VCO. The 20 ns markers from the ÷ 2 counter are
coup ed to enabe gate U300B.
The .2 µs ÷ 2 counter is part of U325. The ÷ 2 counter
output is pin 12 of the integrated circuit, which is supp ied
to enabe gate U330A.
10 ns, 20 ns, or 50 ns and .1 µs, .2 µs, and .5 µs
Enable Gates
Enabe gates for the 10 ns, 20 ns, and 50 ns markers are
U300C, U300B, and U300A respective y, whie the enabe
gates for the .1 µs, .2 µs, and .5 µs markers are U330C,
U330A, and U335A-U335B respective y. U335C is an OR
gate that coup es the se ected .1 µs, .2 µs, or. 5 µs markers
to the decade dividers.
1 MHz Variable Clock
The 1 MHz variabe c ock circuit is an emitter-couped
astabe muti v ibrator. Temperature compensation tran 
sistor Q120, which is the same type of transistor as Q130
and Q135, estabishes the power suppy vo tage for the
mutivibrator. Q130, Q135, and Q140 are the mutivibrator
transistors. Q130 contros the charge current avai ab e to
timing capacitor C127. VR140 provides eve shifting for
the Q1 30 base vo tage. R1 35 contro s the frequency of the
mu tivibrator by contro ing the conduction of Q135. The
ower end of R135 is the higher frequency end whie the
top end reduces the frequency. R145 Variabe Timing
Center, is used to set the frequency of the mutivibrator to
1 MHz when R135 is set to its mechanica midrange
position.
Phase Comparator and Fast-Slow Led's
1 MHz is fed to pin 1 of U150A by either the crysta
reference or the variabe c ock. The 1 MHz crysta
reference is fed t pin 5 f U150B. Pins 12 and 9 of U150
wi go high if the negative edges of the two 1 MHz input
signa s coincide. This occurs when the variab e c ock
frequency is 1 MHz. With these inputs high, U115A
produces a ow that c ears U150A and U150B. The ow now
at pin 9 of U150B and the high now at pin 13 of U150Aare
summed by R152 and R153. The output of the summing
resistors is then fed to the negative input of amp ifier U1 60.
The input signa to U160 is ampified and inverted. The
output of U1 60 is kept from changing rapid y by C160. The
s ow change in the output of U160 causes it to be an
apparent d c eve . If U115B has been enab ed by re easing
the VARIABLE TIMING (OUT) contro , the output vo tage
eve of U160 is app ied to the junction of DS170 and
DS172.
Assume that the frequency has been correct up to this
cyce, pins 9 and 12 of U150 are ow. When the 1 MHz
variab e c ock frequency is s ower than 1 MHz, the
negative edge to the phase comparator wi togge U150B
first. This resuts in a high at pins 9 and 13 of U150 and a
more positive vo tage at the output of U115B. This more
positive vo tage causes DS172 to conduct and become
i uminated.
Again assume that the frequency has been correct up to
this cyce, but this time the 1 MHz variab e c ock frequen 
cy is faster than 1 MHz. The negative edge of the next
cyc e wi togge U150A first, resu ting in a ow at pins 9 and
13 of U150. This in turn causes a more negative vo tage at
the output of U115B, which resuts in the conduction and
i umination of DS170.
Digital Mixer and Counter
The 1 MHz Crysta Reference is counted down by a
factor of 20,000 (2 times 10 4 ) using decade counters U220,
U218, U212, and U210 and fip-fop U215A. The resutant
50 Hz gate frequency (20 ms gate period) avai ab e at the
outputs of U210 is used to contro the disp ay time of the
VARIABLE TIMING % LED. Pin 11 of U210 is the 4-5
output; pin 12 is the ÷ 2 output. The two outputs of U210
are ANDed by U180D to produce a 2 ms pu se, which is
used to c ear BCD counters U1 85 (0.01% digit, which is not
dispayed), U195 (0.1% digit) and U200 (units % digit).
The 1 MHz Crysta Reference and the 1 MHz variab e
c ock output frequencies are compared by digita mixer
U215B, with on y the frequency difference of the two input
frequencies appearing at the output. The output of U215B
is ANDed in U180C with the inverted ÷ 2 output (10 ms
wide gate) of U210. The output of U180C goes to the first
of the three BCD counters.
The 2 ms output pu se of U180D and the 10 ms output
pu se of U115C go to NOR gate U110C. The output of
U110C (which is an 8 ms pu se that determines LED
disp ay time) is one input to AND gate U180B. The other
input to U180B must be a high from U235B to enabe
U180B and cause the LED disp ay to be unbanked. A high
out of U235B is caused by either pressing the VARIABLE
TIMING % contro fu y in to check the LEDs, or by
re easing the VARIABLE TIMING % contro to its out
position. The ow to pin 5 of U235B in the out position of
the VARIABLE TIMING % contro is from pu -up resistor
R450 via CR115 and inverter U115D. In the 521n position
of the MARKER Contro , the cathode of CR115 is con 
nected to ground via S350 to disab e the variab e timing
circuit, since the 1 ns, 2 ns, or 5 ns markers are not
variab e.
3-2
REV B AUG 1980

Theory of Operation — TG 501
Fig. 3-1. Functional block diagram of schematic diagrams 1 and 2 circuitry.
REV B AUG 1980
3-3

Theory of Operation — TG 501
DIAGRAM 3
Decade Dividers
The decade dividers operate continuousy; however,
the output is se ected by enab ing the appropriate enabe
ogic gate with a ow, via the cam switch S350. The -HO
dividers are U355, U360, U362, U364, U368, and U372. The
NAND enabe ogic gates are U330B, U350B-C, U190A-C-
D and U366A-B-C-D. The square-wave pu ses from the
ogic gates are differentiated by an RC circuit using
capacitors C358, C360, C362, C366, C368, C370 and C372.
The resistance for the RC circuit is se ected by cam switch
S350 via the 5-2-1 sequence ogic gates, depending upon
the timing position in the 5-2-1 sequence.
10 ns, 20 ns, 50 ns Marker Output Amplifier
Q390 and Q400 form an emitter coup ed switch that is
contro ed by U300D, and ECL enab e ogic gate. U300D
requires a ow from the 10 ns, 20 ns, or 50 ns ogic gate to
pass the square-wave. The square-wave at output pins 15
and 9 of U300D is differentiated by RC networks C390-
R394 and C400-R400. The differentiated signa is couped
through Q400 as ong as pin 13 of U300D remains ow. The
output from Q400 is summed with the output from the ow
speed marker output amp ifier and supp ied to the
MARKER OUT connector J470.
The se ection of the resistance f r the RC circuit
determines the s ope of the fa ing edge of the marker and
hence contro s the marker brightness. R385, the argest
resistance, is se ected in a positions of the 5-2-1 se 
quence. In the 2 position, a ow from the 5-2-1 sequence
ogic gate turns on Q384 and connects R384 in para e ,
with R385, reducing the resistance and the marker
brightness. In the 1 position, Q380 turns on and R381
para e s R385 to reduce the resistance and brightness
from that obtained in the 2 position.
Q405 provides a stage of iso ation between the decade
dividers and the ow speed marker output ampitude. The
isoation stage increases the impedance seen by the input
to the ow speed marker output operationa ampifier.
Low Speed Marker Output Amplifier
The ow speed marker output ampifier is an
operationa ampifier having a gain of 1.5. The amp ifier
consists of Q408 and Q415 with R406 and R410 being the
input resistor and feedback resistor respective y.
Trigger Output
At MARKER Contro settings of 5 s through .1 µs the
marker avai ab e at the MARKER OUT connector is used
as a s ave trigger. The s ave trigger from the ow speed
marker output ampifier is coup ed through emitter
fo owers Q430 and Q435 and made avai ab e at +
TRIGGER OUT connector J435.
At Marker Contro settings of 50 ns and faster, the
trigger signa rate avai ab e at the + TRIGGER OUT
connector remains .1 µs. The .1 µs output is obtained by
enabing ogic gates U235D and U330D. Enab ing U330D
a ows the output square-wave from U320to be differen 
tiated by RC network R445-C440, then ampified by Q440
before being coup ed to the + TRIGGER OUT connector
via emitter fo ower Q435. The rc network determines the
width and ampitude of the trigger signa , whie R439-C439
network in the emitter of Q440 contro s the signa gain.
R445 High Speed trigger ampitude provides a means of
adjusting the high speed trigger amp itude to match the
ow speed trigger amp itude.
3-4
REV B AUG 1980

Theory of Operation — TG 501
Fig. 3-2. Functional block diagram of schematic diagram 3 circuitry.
REV C AUG 1980 3-5