Tektronix R485 Operating instructions

Tektronix, I nc .
P.O. Box 500
Beaverton, Oregon 97005
070-1193-00
TEKTRCNI»
485/R485
OSCILLOSCOPE
SERVICE
IN S TRUCTION MAN U AL
Se ri al Number
473

485/R485Service
TABLE OF CONTENTS
SECTION 1 SPECIFI CAT ION Page SEC TION 3 CIRCUIT DESCRIPTION (cont)
Page
Introduction
1-1
Focus DC Restorer
3- 13
Vertical Deflection System 1-1
Beam Current Limit 3- 14
Probe P erformance 1-3 Power Supply Shutdown Caused by
A and B Triggering 1-3 Excessive Beam Current 3-14
Horizontal Deflection 1 -4 C RT Control Circuits 3- 14
Calibrated Sweep Delay 1-4 Auto Focus Circuit
3- 14
X-V 1-6 Calibrator
3- 15
CRT
1-6
Calibrator 1-6
Other Characteristics 1-6 SECTI
ON 4 MA INTENANCE
EnvironmentalC ha racteristics 1-6
Introdu ction
4-1
Cover Removal and Rainstallation 4-1
SECTION 2 OPERATING INSTRUCTIONS Cleaning 4-1
Lubri cation
4 -2
General 2-1 Visual Inspection
4.3
Preliminary Inform ation 2-1
Semiconductor Checks 4-3
Controls and Connections
2:1 Recalibration 4-3
Front Panel 2-1 Troubleshooting 4-3
Rear Panel 2-4
In troduction
4.3
Bottom Side 2-4
Troubleshooting Aids 4.3
Circuit Boards
4-3
Troubleshooting Equipment
4-5
Troubleshooting Techniqu es 4-6
SECTION 3 CIRCUIT DESCRIPTION Special
Troublesho oting Infor mation 4-7
CorrectiveMaintenance 4-11
l ntroduction 3-1 Obtaining R eplacement Parts
4-11
50 n Attenuator 3-1 Soldering
Techniqu es
4-11
1 Megohm BufferAmplifier 3-1
Component Replacement
4- 12
50 n Overload Protect ion 3- 1
Circuit Board Replacement
4-12
Vertical Preamplifier 3-1 Timing Board Removal
4-12
Transformer Board Removal 4•13
Signal Channel Switch 3-2 Inv
erter Board Removal
4-14
Inter nal Trigger Amplifier 3-2
Semico ndu ctor Replacement
4-14
Main Vertical Amplifier 3-2
Circuit Board Pins
4-14
Scale Factor Readout 3..J
End Lead Pin Connectors
4-15
Vertical Mode Control
3.3
Cathode Ray Tube Rep l acemen t
4-15
Z Axis
3.3
Repackaging for Shipment 4-15
A Trigger Amplifier
3-3
lnt erboard C9mb Connection Locations 4-16
A EXT Trigger Identify 3-3 SECTION 5
CAL I BRAT ION
A Trigger Generato r 3-4
B Trigger Generator 3-4
In troduction 5-1
A and B Sweeps 3-4
TEKTRONIX FieldService 5-1
Horizonta l Amp lifier 3-6
Using Th is Procedure 5-1
Horizontal Control 3-6
Test Equipment Required 5-1
Power In verter/Regula tor
3-6 Special Calibration
Fixtures 5-1
Line Filter
3-6
Ca libration Equipment Alternatives 5-4
Line Input Circuit 3-6
Performance Check 5-4
Start Network 3-7
Calibration Procedure 5-8
Inverter 3-8
Inverter /Regulat or 3-8
Inverter Current Limiting Circuit 3-8
SECTION 6 RACKMOUNTING
Overvoltage Stop Circuit 3-8 I
ntroduction 6-1
Line Stop Circuit and Surve Limiting 3-8 Rack Dimensi
ons 6-1
Procedure for Converting the 485 to
Slide Out Tracks 6-1
DC Operatio n 3-9
Mounting Procedure 6-1
Low Voltage Supplies 3-9
Alternate Rear Mounting Methods
6-2
Power Supply Protection Circuit 3-10 Removing or Installing the In strument 6-2
Stop Monostable 3- 10
Slide Out Tr ack Lubrication
6-2
Balance Node
3.• 10
Overcurrent Protection 3- 12 SECTION 7 ELECTRI
CAL PARTS LIST
Low Line Voltage Protection
3- 12
Samp ling Period Timer and Over- SECTION 8 DIAGRAMS
AND CIRCUITBOARD
Vo ltage Protection 3- 12
CRT Circuit 3- 12 ILLUSTRATIONS
Filament Voltage 3- 12
High Voltage Supplies 3- 12
Anode S upply 3- 12 SEC TION 9 MECHANICAL PARTS LIST
Cathode Supply 3-12
Cathode Regulator 3-12
Grid DC Restorer 3- 13
CHANGE INFORMAT ION
REV. B, MAR. 1976

485/A485 Se .
rvrce
Th e 48S p
onable Osc: · 11
I OSC:Ope.
®

Section 1 -485 / R485 Service
SPECIFICATION
Introduction
The 485 /R 485 is a general-purpose, environmentalized,
high-performan ce, portable, wide-band os ci lloscope which
has a dua l-channel vertical amplifier wit h selectable input
impedance (DC to 350 MHz bandwidth with 50 n input
impedance; DC to 250 MHz bandw i dth wit h 1 Mn input
impedance). The 485 has a 1 ns sweep rate, stable triggering
to bandwidth limits and calibrated X-Y capabilities.
Del ayed sweep has calibrated delay time, can be trigger ed
after delay and can be displayed with the intensified main
sweep in an alternate sweep switching display. Additional
features are X 10 , X100 probe scale factor readout, 8 div
X 10 div graticule ar ea, sma ll spot size and high writing rate.
A 20 MHz bandw i dth limiter, 1 MH z and 1 kHz fast-rise
cali brator and autofocus are also included. Th e 50 .Q inp ut
is automatically disconnected from excessive voltages. An
external trigger view feature is also provided. Th e 485-1 and
485-2 have no external trigger view. The 485-2 has only 50
n vertical input impedance.
ELECTRICAL CHARACTERISTICS
VERTI CAL DEFLECTION SYSTEM
(2 iden tica l channels)
Se lectable Input Imp eda n ce
50 n wit hin 0.5 %. VSWR ,s;;:; 1.25:1 on 5 mV/div and
10 mV/div, 1.15 :1 from 20 mV to 5 V/div to 350 MHz.
1 M.Q withi n 1% pa ralleled by approximately 20 pF.
Bandw idth
1 and Riset
ime
2
(VA RI ABLE gain
CA LIBR AT ED
3)
From 50 n Terminated Source
- 15 °C to +35°C
From 50 n terminated source - 15 °C to +35°C.
50 n DC to at l east 35 0 MH z, 1 ns
1 Mn DC to at least 250 MHz, 1.4 ns
1Bandw
idt h (BW) measured at -3 dB down .
2Risetime calculated
from 0.35 /B W. From +35 °C to + 55 °C, BW is
300 MH z f or 50 n and 200 MH z for 1 M n.
3See Fig. 1-1
for effect of VAR I ABLE gain co n trol.
REV C. MAR 1979
I nput Coupling Se lection
AC; DC; GND (provides zero reference, precharges
coupling c apa citor, disconnects 50 n load in 50 n
model.
L ower - 3 dB Point (AC coup li ng from 50 n
source)
50 n inpu t, 1 kHz or less.
1 Mn input 1X , 10 Hz or less.
Defle ct ion F actor
5 mV/div to 5 V/div in 10 calibrated steps (1 -2-5
sequence). accurate within 2%. Uncalibrated, continu-
ously variable between steps to at least 12 .5 V/div.
Lights at edge of knob skirts indicate correct deflection
factor for 1 X, 10X and 100X probes.
Gain can be recalibrated at front panel. 1 M.Q BAL is
avai lab le at bottom panel to eliminate step attenuator
shift above 10 mV /div, in the 1 Mn mode.
Display Modes
Channel 1; Alternate; Chopped (approximately 1 MHz
rate); Added; X-Y (CH 1 - Y and CH 2 -X); Channel 2
(+ Up or Inverted).
In te rn al Tri gger Sour ce
Normal (displayed signal). Channel 1 or Channel 2
signal.
500
I
400
300
,_/
---
----
--
--
200
BW ,
MH z
TY P ICAL BANDWIDTH , 50 n
VS .
VARIABLE GAI N SET TING
100
50
50%
100 %
Percent of CAL Gain
Fig. 1-1. Typ ical Bandwidth , 50 n vs. Var ia ble Gain Setting (varies
considera bl y depending on i nstrument SN)
1-1

Specification-485 / R485 Service
..
"'
!l
0
>
~
0.
Q.
<(
100 V
60V
40V
20V
10 V
6V
4V
2V
1 V 0.1 ms
NONRECURRING SIGNALS
IN THIS AREA DO NOT
TRIP THE DISCONNECT
1 ms 10 ms
TYP I CAL
50 n PROTECTION
------It-- DISCONNECT
CHARACTERI S TIC
0.1 s
5 V
1 s
Ti me from Start of Applied Vol tag e
Fig. 1-2. Typical 50 n Protec tion Disconnect Characteristic.
50 n Protection
Internal detection circuitry automatica ll y disconnects
excessive signals of up to 50 V. The disconnected
condition is indicated, a nd h as manual reset.
Maximum I nput Voltage
50 U Disconnect occurs fo r voltages that exceed approx-
imately 5 V RMS continuous or 0 .1 watt-second fo r
instantaneous voltages of 5 V to 50 V.
Repeated application of voltages in excess of 50 vo lt s
and greater than 0. 1 watt-second will cause deterioration
of K1S1 relay contacts, due to arcing. Signa ls in excess
of 150 volts will damage the instrument.
1 MU-DC coupled 2 50 V (DC + peak AC), 5 00 V P -P to
1 kHz. AC cou pl ed 5 00 V (DC + peak AC), 500 V P-P to
1 kHz.
Common Mode Rejection
Added Mod e wi th Channel 2 inverte d. At least 10:1 at
50 MHz for 8-division signal a fter adjusting CH 2 gain
for best CMR at 50 kHz and 20 mV /div.
1-2
Bandwidth Limiter
Lim its to appr ox imate ly 20 MHz the Vertical Am pl i fi er
an d Internal Tr igger signals.
Channel Isol ation
At least 30 :1 at 350 MH z.
A Ext Trigger Display (R485 and 485 onl y)
Momentary pushbu tt on in V ERT MODE area enabl es
di splay of EX T A Trigger when A source is in EXT
p os i tion. De fl ec tion factor is approximately 50 mV /div .
Risetime is approximately 1.5 ns. Delay match to CH 1
or CH 2 input is wi th in 0 .5 ns at 50% amplitude.
Triggering l eve l is wi th in 0.5 div of center-screen.
Probe Power
T wo 4-pin connectors at the rear of the instr um ent
provide power suitable for op tional ac tiv e pr o bes such as
the P 620 1.
®I

Specification-485/R485 Service
PROBE PERFORMANCE
(Prob es are Optional Accessories)
Temperature Range
Lo wer Bandwidth
for thi s
Input
-3 dB point with 485
Ba nd width
Type
Atten . Impedance (max imum ) (minimum) Specification
For Use With 50 n Input
P6056 010.-6056-03 - 6 ft.
010- 6056 - 05 - 9 ft.
,ox
soon
1 pF 200 Hz
350 MHz
010-6057- 03 - 6 ft. -
15 °C to + 35 °C
P6057
100X 5 kn 1 pF
20 Hz 350 MHz
010 -6 057 - 05 - 9 ft.
1X 100 kn 3 pF 10 Hz
P6201 0°C
to + 35 °C
010 -6201-01 - 6 ft. Plug- 10X 1 Mn < 1.5 pF 1 Hz
330 MHz
(FET Prob e)
On 1
00X 1 Mn < 1.5 pF 10 Hz
For U se With 1 Mn I nput
010 -60 53 - 11 - 3 1/2 ft .
P6053A
010 -6053-13 - 6 ft.
010 - 6053 - 15 - 9 ft .
A and B TR IGGERING
A Tr igger Mod e
NORMAL.
Sweep runs only when triggered.
AUTOMATIC.
,ox
Sw eep free-runs in the absence of a triggering signal
and for si gnals below 20 Hz.
S IN GLE SWEEP.
Sweep runs one time on the fi rst triggering event after
pressing the reset selector.
B Trigger Mode
BRUNS AFTER DELAY TIME.
Starts automatically at th e end of the delay time.
B TRIGGERABLE AFTER DELAY TIME.
Runs wh en tr i gge red. Th e B (delayed) sweep runs
once, in eac h of these modes, following the A sweep
delay time.
REV. B, AUG. 1977
1 Mn
1 Mn
1 Mn
9.5 pF 250
MH z
12 pF 1 Hz 250 MHz - 15 °C to +35 °C
13.5 pF
200 MHz
Time Ba se A and B Trigger Sensitivity
Trigger Mod e To 50 MHz At 350 MH z
DC I nt 0.3 div 1.5 div
DC Ext 20mV 100 mV
AC Signals below 16 Hz are attenuated.
LF Reject Signals below 16 kHz are attenuated.
HF Reject Si gna ls bel ow 16 Hz and above 50 kH z
are attenuated.
L eve l and Slope
Internal, permits selection of tri ggering point at any leve l
on the positive and negative slope of the d is played
waveform. Ext ernal, level is ad ju stable through at least
±0.5 V for eit her polar i ty (± 5 V for EX T ..;- 10).
A Source
Int ernal, Lin e. Ex ternal, External ..;- ,o,
1-3

Specification-485/R485 Service
B So ur ce
B runs after Delay Time, Internal, External, External
~10.
External Inputs
1 MU paralleled by approximately 20 pF. Maximum
input voltage 500 V (DC + peak AC) , 500 V p.p to
1 kHz.
Jitte r
Less than 0.1 ns at 350 MHz and 1 ns/div.
HORIZONTAL DEFLECTION
Time Bas e A and B
1 ns/div to 0.5 s/div in 27 calibrated steps (1·2·5
sequence). Uncalibrated, A is continuously variable
between steps and to at least 1.25 s/div.
Time B ase A and B Sweep Accuracy (Center 8
scree n division s)
Sweep Rate
+15°C to +35°C - 15°C
to +55°C
1 ns /d iv to 20 ns/div ±3% ±5%
50 ns/div to 0.1 s/div ±2% ±4%
0.2 s/div to 0.5 s/div ±3% ±5%
Di splay Modes
A, A INT El--lsified during B delayed, ALTernate display
of A INTEN and B (delayed sweep). Only A sweep is
displayed for A sweep rates of 1, 2 and 5 ns/div.
1-4
Minimum Sweep Holdoff (A Trigger H oldoff in
Norm detent)
A Time Setting
1 ns/div to 0.1 µs/div
0.2 µs/div
0.5 µs/div to 0.5 s/div
A Trigger Holdoff
Less than 0.4 µs.
Less than 1.0 µs.
Less than 2 times the
A TIME/DIV sett ing.
Adjustable control permits a stable presentation of
repet itive complex waveforms. The control covers at
least the ti me of one full sweep for sweeps faster than
0.2 s/div.
B Ends A
The A sweep is reset at the end of the B sweep to allow
the fastest possible sweep re pet ition rate for increased
trace intensity in the delayed sweep mode.
CALIBRATED SWEEP DELAY
Delay Time Range
0 to 9.9 times the De la y Time/Div settings of 10 ns/div
to 0.5 s/div.
Differential Delay Time Ac curacy (+15°C to
+35°C)
Exclude th e first (above 0.0) 1.0 turn or the first 40 ns
of the DE L AY dial.
DE L AY TI ME Setting
10 ns/div and 20 ns/div
50 ns/div to 1 ms/div
2 ms/div to 0.5 s/div
± (1% of mi::asurement
+0.2% of full scale3)
± (0.5% of measurement
+0.1% of full scale)
± (1% of measurement
+0.1% of full scale)
3Full scale is
lOX the Delay Time/Div Setting.

i
!'!
::,
"
u
<(
3.0
2.0
1.0
I
\
\
SPECIFIED DIFFERENTIAL
\
DELAY ACCURACY
--
\
vs . --S
IZE OF MEASUREMENT
\ \ 1\-.
' '
r-,...,.._
I I I I I
----
"
.......
,.__ 10 nstdiv & 20 ns/d iv
\ ~r------
'
........
2 ms/d iv to 0.5 s/d iv -
r-- -
~so ns/div to 1 ms/div
~:t (0.5 % of measurement
+0.1% of full sc:ale)
2 3 4 5 6 7 8 9
10
DIFFERENCE Between Two Dial
Readings. Major D.T .P. Divis ions
Fig. 1-3. Specified Differential Delay Accuracy vs. Size of Measure-
men t.
Jitt er
Less than 0. 005 % (one part in 20,0 00) of fu ll scale plus
0.2 ns. (Wrap-around cover must be in place.)
X·Y
Full Sensitivity
(CH 1 V ert, CH 2 H orizonta l.) 5 mV/div to 5 V/div in
10 calibrat ed steps (1-2-5 sequence) accurate within 2%.
Gain can be recalibrated at front panel.
Y Performance
Identical to CH 1. See Vertical Deflection.
X-Axis Bandwidth
DC to 4 MHz (with 10 div reference signal).
X-Y Ph ase Match (Fu ll BW and BW Limit)
Within 3° to 4 MH z.
X-Gain Match to CH 2
+1 5°C to +35°C: 1%
- 15 °C to +55°C: 3%
Specification-485/R485 Service
CRT
TEKTRONIX CRT
4-inch rectangular tube; BX 10 divisions (0.8 cm/d iv )
display area. P31 phosphor normally supplied; P11
optional without extra charge. 21 kV accelerating
potential.
Photographic Writing Speed
At least 3 div/ns for standard P31 phosphor; at least
6 div/ns for opt ional P11 phosphor (with the
TEKTRONIX C-31-R Camera and POLAROID 10,000
ASA film).
Auto Focus
Autom atically maintains beam foc us for all intensity
se tting s. (Intensified z on e and EXT Z axis are not
auto - focused).
Graticule
Internal, no parallax. Variable ed ge-lighting. Markings
for measurement of risetime. Graticule is dark with
illumination off.
Beam Fi nder
Limits display within graticule area.
External Z-Axis
Risetime 15 ns. Inp ut R 500 n. +o.2 V (DC to 20 MHz)
blanks trace of average intensity. +2 V (DC to 2 MH z)
blanks maximum intensity trace.
Beam Current Lim it
Automatically limits th e average beam current to protect
the CRT phosphor. (Limi ts average current to 20 µA for
sweep rates faster than 50 ms/div; 5 µA for 50 ms/div
and slower sweep rates and for X-Y . Backup system
shuts down power supply if average current reaches
approximately 30 µA.)
1-5

Specification-485 / R485 Service
CALIBRATOR
Two - Frequency Fast-Rise Calibrator
Accuracies +
15 °C to +35°C -
15 °C to +55°C
5 V amplitude to
1 Mn load
0.5 V amplitude to
50 n±0.5% load
50 mA amplitude to
optional BNC acces-
so ry current loop
Selectable Frequency
of 1 MHz and 1 kHz
Output Resista nce
450U
Risetime
0.5% 1%
1% 1.5%
1%
1.5 %
0.25% 0.5%
Positive edge into 50 n, less than 1 ns. Overshoot and
ringing less than 2% into 50 n at 1 GHz bandwi dth.
1 kHz Duty Cycle
49.8 % to 50.2 %
OTHER CHARACTERISTICS
Signal Output s
Positive gates from both time bases (approximately 4 V).
and a positive-going Sawtooth from Time Base A
(approximately 10 V). Gates and Sawtooth are approxi-
mately 0.5 V amplitude into 50 n.
Power Requir ement
Two-position line volt age sele ct or 115 V (90 V to
136 V) a nd 230 V (180 V to 272 V) 48 to 440 Hz. 60
watts maximum at 115 V and 60 Hz. 0.9 A maxi mum at
115 V and 60 Hz. Line fuse: 3 A fast.
Coo ling
Quiet, fi lt ere d. fo rced -a ir ventilation. Fan speed
increases smoothly wi th increasing ambient temperature.
ENVIRONMENTAL CHAR AC TERI STICS
Amb i ent Temp era tur e
Operating: - 15°C to + 55 °C
Storage: - 35 °C to + 75 °C
1-6
Altitude
Operating: to 15 , 000 feet . Maximum a ll owa bl e ambient
temperature decreased by 1°C per 1000 feet from 5,000
to 15 , 000 feet.
Nonoperating: to 50,000 feet.
Vibration5
Oper at ing: 15 minutes along each of the three axis,
0.025 inch peak-to-peak displa cement (4 g's at 55 Hz)
10 to 55 to 10 Hz in 1- minute cycles.
Shock
5
Operating and No nope rating: 30 g's, one half sine,
11 -ms duration, 2 shocks per axis in each direction for a
total of 12 shocks.
Electromagnetic Interference
{With 485 EMI modification option 4). Meets inter-
ference requir ements of M IL -1-6 180 : power line
conducte d, 150 kHz to 25 MH z; radi ated, 150 kHz to
GHz.
Humidity
Operating and Storage: 5 cycles ( 120 hours) to 95 %
relative humidi ty referenced to MIL-E-16400F {par.
4. 5.9 through 4.5.9.5.1, class 4) .
Dimen sions and Weight
Height: 6 and 9/16 inches.
Width: {with handle) 12 inches.
Depth (including panel cover): 18 a nd 1/2 inches.
Depth (handle extended): 20 and 5/8 inches.
Ne t weight {without ac ce ssory case and panel cover): 21
pounds.
Net weig ht (with panel co ver. accessory case and
a cc essories): 24 pounds.
D omest ic shipping weig ht : 31 pou nd s.
E xp ort-packed weight: 42 pounds.
5R485 s
trapped to table . not mount ed in rack.

Section 2 -485 / R485 Service
OPERATING INFORMATION
General
To effectively use the 485, the operation and capabilities
of the instrument must be known. This section describes
the operation of the controls and connections and gives
first-time and general operating information.
PRELIMINARY INF ORMAT ION
Operating Vo lt age
WARNING I
This instrument is designed for operation from a
power source with its neutral at or near earth
(ground) potential wi th a separate safety-earth
conductor. It is not intended for operation from two
phases of a multi-phase system, or across the legs of a
single-phase, three-wire system.
The 485 can be operated from either a 115 V or 230 V
nominal line voltage source, or a 220 V external battery
pack. The Line Voltage Selector switch on the rear panel
converts this instrument from one operating voltage to the
other.
Power Cord Conductor Identification
Conductor Color
Alternat e Color
Ungrounded (Line) Brown Black
Grounded (Neutral) Blue
Wh i te
Grounding (Earthing) Green-Yellow Green-Yellow
~
This instrument may be damaged if operated with the
Line Voltage Selec tor switch set to incorrect posi-
tions for the line voltage applied.
115 V
230 V 90-136 V 180-272 V
The 485 is designed to be used with a three-wire AC
power system. If the t hr ee to two-wire adapter is used to
connect this instrument to a two-wire AC power system, be
sure to connect the ground lead of the adapter to eart h
(ground). Failure to complete the ground system may allow
,he chassis of this instrument to be elevated abo ve ground
potential and pose a sh oc k ha za r d.
REV . C, MAR. 1977
Operating Temperature
The 485 can be operated where the ambient air
temperature is between -15 °C and +55 °C (+5° F and
+131°F). This instrument can be stored in ambient
temperatures between -55°C and +75°C (-67 ° F and
+ 167 °F). A fter sto ra ge at temperatures beyond the opera-
ting li mits, allow the chassis t emperatu re to come within
the operating limits before power is applied.
The 485 is cooled by air entering through the air filter
on the rear panel and exiting through the holes on the sides.
Adequate clearance must be provided at these locations.
Allow at l east one inch clearance behind the air fi l ter and at
least one inch on the sides.
A thermal cutout in this instrument provides thermal
protection and disconnects the power to the instrument if
the internal temperature exceeds a safe operating level.
Power is automatically re stored when the temperature
returns to a safe level. Clean the air filter periodically; a
di rt y filter prevents adequate air flow into the instrument.
CONTROLS AND CONNECTORS
General
The major controls and connectors for operation of the
485 are locat ed on the front panel of the instrument. Some
auxiliary functions are provided on th e side, top, bottom
an d rear panel. To make full use of the capabilities of this
instrument, the operator should be familiar with the
function and use of each of these contro ls and connectors.
A brief descrip tion of each contro l and connecto r is given
here.
Front Panel
POWER Pushb utton Turns instrument on or off.
CAL 5 V Connector BNC connector for square-wave
voltage calibrator output signal.
FREQ Pushbutton Selects one of two frequencies (1
kHz or 1 MHz) for the fast-rise
calibr ator signal.
INTENSITY Cont rol Controls intensity of writing beam.
B INTENSITY Provides additional intensity con •
Control trol fo r the B SWEEP.
2-1

Oper at ing ln for matio n-485 /R 485 Se rvi ce
SCALE IL LUM
Control
BEAM FINDER
Pushbutton
BW LIM IT
Pushbutton
20 MHz I ndicator
VERT MODE
Push button Selector
CH 1
ALT
CHOP
ADD
X-Y
CH 2
INT TRIG
Pushbutton Selector
NORM
CH 1
CH 2
VOL TS/D IV Switch,
CH 1 and CH 2
2-2
Contro ls illumination of internal
CRT graticule.
Compresses trace within graticule
ar ea, regardless of position con trol
se tt ings or amplit ude of signal
app lied.
limits to approximately 20 MHz
the bandwidth of t he vertical ampli·
fier system and of the INTernal
TR IGger signal.
ligh ts when bandwidth of vertical
amplifier is being limi ted.
Displays Channel 1 on l y.
Dual trace display by switching
between channels at the end of A
sweep .
Dual trace display by switching
between channels every 0.5 µs (1
MHz chopped display).
Alge br aically adds CH 1 and CH 2
input signals.
Permits X-Y operation. Displays CH
1 signal on the vertical (Y) axis and
the CH 2 signal on the horizontal
(X) axis, with a 4 MHz phase-
compensa t ed bandwidth.
Displays CH 2 only.
T he signal being displayed is the
internal trigger source.
Selects CH 1 as the internal trigger
source.
Selects CH 2 as the int ernal trigger
source.
Selects 1X calibrated deflection
factors from 5 mV/div to 5 V/div in
ten steps (1-2·5 sequence). Attenu -
ating probe tip deflect ion factors
for X 10 and X1 00 coded probes are
automatically indicated by the
three readout lamps at the circum-
ference of this knob. All three
lamps are off when the channel is
VARIABLE volts/div
Con tro l, CH 1 and
CH 2
GAIN Adjustment,
CH 1 an d CH 2
A EXT TRIG
P ushb u tton
(momentary not on
485- 1 and 4 85-2)
1 Mn/50 n Switch,
CH 1 and CH 2
(485-2 has RESET-
PUSH)
RESET I ndicator
I nput Selector Switch,
CH 1 and CH 2
AC
GND
DC
I nput CH 1 or Y
Connector and CH 2
or X Connector
POSITION Controls,
CH 1 and CH 2
not selected for display by the
VERT MODE selector, or when
using probe IDENT ify .
Provide continuously variable
deflection fac tors between calibra-
ted steps. Maximum def l ect i on
factor range is extended to
1 2. 5 V /div. Push-away control
provides calibrated deflection fac-
tor in the CAL IN position.
Screwdriver adjust ment allows cali-
bration of vertical def l ect i on factor .
Overrides other vertical contro ls to
display the externa l signal be ing
used for A sweep triggering.
Il l uminated push- push selection for
input impedance. Is also used to
reset 50 n overload condition
(1 Mn/50 n switch must be pushed
twice to return to 50 n input
impedance). 485-2 is non -
illuminated momentary switch for
RESET only.
When maximum input power is
exceeded in the 50 n mode causing
the overload disconnect to operate,
the RESET indicator is illuminated,
and the 1 M n/50 n lamp is turned
off.
Capacitively couples input signal to
vertical amp lifier.
Grounds the amplifier input and
permits precharging the AC input
coup ling capacito r. 50 n termina•
tion disconnected in th e 50 n
mode .
Signal is di r ect ly coup l ed to the
vertical amplifier.
BNC connectors for applying exter·
nal signals. Included are concentric
coding rings for probes with scale
factor and identify switching.
Vertically positions the display. In
X·Y mode, CH 1 controls positions
in the Y (vertical) axis and th e CH
2 contro l positions in the X (hori-
zontal) axis.

CH 2 POLARITY
Switch
HORIZ DISPLAY
Pu shbutton Selector
(Blue Panel
Background)
A
INTEN (A)
ALT
B (DLY'D)
TRACE
SEPARATION
Control
T rigge ring Source
Switch, A TRIGGER-
ING and BTriggering
INT
LINE (A
TRIGGERING
only)
BRUNS AFTER
DELAY TIME (B
TR IGGERI NG
Only)
EXT
EXT10
Triggering COUPLING
Switch, A TRIGGER-
ING and BTRIGGER-
ING
AC
LF REJ (AC
Coupled)
HF REJ (AC
Coupled)
+UP and INVERT slide selector
provides for inverting CH 2 display.
(Inoperative in the X-Y, VERT
MODE, and when timing knobs are
locked in the 1, 2, and 5 ns/div
position.)
Displays A sweep.
Displays A sweep intensified (after
the delay time) for the duration of
Bsweep.
Alternately provides INTEN (A)
and B (DLY'D) displays.
Displays B (DLY'D) sweep.
Provides additional positioning to B
(DLY'D) display in the ALT hori-
zontal display mode.
(Green Panel Background)
Us es the signal selected by the INT
TRIG switch as the triggering
signal.
Uses a portion of the line-frequency
voltage as a trigger signal.
B runs automatically after the time
selected by A TIME/DIV and the
calibrated DELAY TIME POSI-
TION control.
Permits triggering on signals applied
to t he EXT TRIG INPUT
connector.
Attenuates external trigger signal
by a factor of 10.
Trigger signals are AC (capacitively)
coupled to the trigger circuitry.
Trigger signals below 16 Hz are
attenuated.
Attenuates triggering signals below
16 kHz.
Triggering signals below 16 Hz and
above 50 kHz are attenuated.
DC
Operating lnfor mation-485/R485 Service
DC (direct) couples a ll trigger sig-
nals to the trigger circuitry.
EXT TRIG I nput
Connector
SL OPE Switch, A
TRIGGERI NG and
BTRIGGERING
LEVEL Control, A
TRIGGERI NG and
BTRIGGERING
TRIG'D Indicator
SWEEP MODE Switch,
A TRIGGERING
AUTO TRIG
NORM TRIG
SINGLE SWEEP
RESET
READY Indicator
A TRIGGER
HOLDOFF
DELAY TIME
POSITION
A and BTIME/D IV
AND DELAY TIME
Switch
BNC connector providing input for
external trigger signals.
Permits triggering the sweep on the
positive or negative-going portion
of the trigger signal.
Selects amplitude point on th e
triggering signal where sweep·
triggering occurs.
Lights when A sweep is triggered.
Permits normal triggering on wave-
forms with repetition rates of at
least 20 Hz. Sweep free-runs in the
absence of an adequate triggering
signal.
Permits normal triggering. No CRT
display in the absence of an ade·
quate trigger signal.
Displays one sweep only until reset.
A momentary-contact position of
the SWEEP MODE switch that pro-
vides for re-arming the A sweep
generator during th e SINGLE
SWEEP mode of operation.
Is illuminated when A sweep is
armed in th e SINGLE SWEEP
mode.
Adjustable control of the time
between sweep steps, permits a
stable presentation of repetitive
complex waveforms. The control
covers at least the time of one full
sweep for a ll but th e two slowest
sweeps.
Ten-turn calibrated control delays
B sweep start (or B trigger arming)
from 0 to 9.9 times the Time Base
A TIME/DIV setting after the start
of A sweep.
Selects calibrated A and B sweep
rates from 0.5 s/div to 1 ns /div in
27 steps (1-2-5 sequence). Delay
Time operation extends from
0.5 s/div to 10 ns/div.
2-3

Operat in g l nfo rmation -4 8 5/ R485 Se rvi ce
A VAR I ABLE
Control
DLY'D SWEE P
PULL Knob
POS ITION (hori•
zontal) Control
Rear Pa n el
Pr ovides continuously variable A
sweep rate to approximately 2.5
times the calibrated setting (uncali-
brated sweep rate is extended to
1.25s/div). Push away control
provides calibrated rate in the CAL
IN position.
Provides for advancing the B
(DL Y'D) sweep rate ahead of the A
(DELAY ING) sweep rate. (When A
rate is 1, 2, or 5 ns/div the concen-
tric knobs are locked together, and
only the A swee p is displayed.)
Horizontally positions trace. I n-
operative in X-Y mode.
TRACE ROTATION Screwdriver adjustment to align
Adjustment trace with horizontal graticule lines.
FOCUS and ASTIG
Adjustment Adjustment
used to obtain a well
defined display. Requires infre-
quent readjustment.
B+GATE BNC Connector providing a
positive-going rectangular waveform
coincident with Bsweep.
A +GATE BNC connector providing a
positive-going rectangular waveform
coincident with A sweep.
A SWEEP Connector BNC connector provides a sample
of A sawtooth generator signal.
2- 4
Z AX IS INPUT
Connector
PROBE POWER
LI NE CORD
LI NE VOLTAGE
SE LECTOR
OPERATING TIME
Bottom Side
1 M.Q BAL,
CH 1 and CH 2
BNC input connector for intensity
modulation of the CRT display.
Two 4-pin connectors at the rear of
the instrument provide power suit•
able for optional active probes such
as the P6201.
Power cord is a 3-wire, permanently
attached cable, approximately 7.5
feet in length.
Recessed slide swi tch selects nomi -
nal operating line range. 115 V (90
to 1 36 Vl or 230 V (180 to 272 V l.
Elapsed operating time indicator.
5000 hr. scale.
Adjustment provides for DC ba t•
ance of 1 Mn Buffer amplifier.
NOTE
Two types of crt graticules have been used in some
Tektronix oscilloscopes. One graticule has 0% and
700% risetime reference points thatare separated by
6 vertical graticule divisions. The other graticule has
the 0% and 100% risetime reference points separated
by 5 vertical divisions. In your manual, illustrations
of the crt face or risetime measurement instructions
may not correspond with the graticule markings on
your oscilloscope.
REV. 8, MAR . 1976

Section 3-48 5/ R485 Servi ce
CIRCUIT DESCRIPTION
Introdu ction
This section describes the electrical operation and
relationship of the circuits in the Type 485. The theory of
operation for circuits that are used only in this instrument
are described in detail in this discussion. Circuits that are
com monly used in the electronics industry are not
described in detail.
50 n ATTENUATOR
Two identical attenuators, one for each vertical channel,
are used to sel ect the desir ed vertical sensitivity of the 485.
Each attenuator is an integral unit conta ining various 50 n
attenuators, input overl oad protection ci r cuitry and, where
applicable, a 1 megohm attenuator and 1 megohm buffer
amplifier.
The 50 n attenuator is comprised of a delay line,
DL410, and four 50 n attenuator sections. The + 2 and +
2.5 50 n attenuator sections are shared by a 1 Mn buffer
amplifier. The two + 10 attenuator sections are used only in
the 50 U mode. The delay line equalizes the delay
differences between the 1 Mn buffer amplifier and the
50 n mode. R127 provides termination for the 1 Mn
buffer amplifier when the instr ument is operating in the
50 n mode.
1 MEGOHM BUFFER AMPLIFIER
The 1 megohm buffer amplifier provides a high input
impedance and unitY gain when terminated in 50 n. It is
connected to the input th ro ugh relay K1Sl only in the 1
megohm mode and when the RESET light is on.
C33 and R33 provide input current limiting. CR33
clamps negative transients in excess of 9 .6 V to protect
FET 034. The gate to drain junction of 034 gives clamping
for positive-going overloads. The high frequency signal path
goes from the input FET to 040, an emitter fo ll ower. R53
sets the high frequency gain. 060 drives 062; CR62
balances out the base-em itter voltage of 062 and temper-
ature compensates it to keep the standing c urr ent in 062
independent of temperature. 062 current drives the output
for positive signal swings. 060 also drives 070, which pulls
the output negative through R69 and serves as reverse
term ination at high frequencies. CR64 and CR65 work as
expanders for high amplitude signals. R55 and C55 are high
frequency adjustments which affect the first five nano-
seconds of the transient response. L56 and L71 are integral
parts of the ci rcuit board providing high frequency peaking.
050 is a low impedance drive for the low frequ ency
feedback path.
®
L ow frequency feedback is accomplished by U48, which
compares the voltage levels at the base of 040 and the
output, J70. C46 matc hes the time constant of C77 and
R 75 with the time constant of R42 and parallel combina-
tion of C4 6 and C47. C48 sets the bandwidth of U48.
50 n OVERLOAD PROTECTION
In the 50 n mode, K1 is closed by U SO, which routes
the signal to the 50 n attenuator. 50 n input prot ec tion is
provid ed by an RMS detecting circuit in USO. R84 and
R1 07 attenuate the i nput signal l 00X for USO. C86, C87,
and R87 integrate a signal proportional to the RMS value of
the signal at pin 3 of USO. When an overload is detected,
Kl is de-energized, removing the signal from the 50 n
atten u ator section and applying it to the input of the 1
megohm buffer amplifier. USO also lights DS96, the RESET
light. To reset, Sl 258 is switched to the 1 megohm
position, causing the scope to be in the 1 megohm mode.
Ret urn to the 50 n mode is then accomplished by pushing
S125B (50 n/ 1 megohm mode switch) again.
VERTICAL PREAMPLIFIER
CH 2 is identical to CH 1 except that CH 2 has a polarity
switch. Only CH 2 wi ll be described here. The CH 2 signal is
received from the CH 2 attenuator through J300 . Diode
bridge CR301, CR302, CR303, and CR304 protects the
input from large signals that occur too fast for the input
protection relay to r eact. T305 is a balun, providing a
push-pull signal to U310 at hi gh frequencies. The 50 n
input termination consists of R308, R305, and R309. R308
is adjusted to give 50 n DC resistance at input connector
Jl. CH 2 offset control R306 adjusts the voltage at th e
input connector Jl to zero in the absence of an input
signal. Either R310 or R312 is selected by the POLARITY
switch S310, allowing the variable control to be balanced in
both invert and normal modes. The output leads of U310
(pins 5, 6, 8, and 9) are crossed over so that the polarity of
the si gnal can be inv er t ed. R90, the variable contro l, and
the resistor network R317, R319, R325, R326, R327, and
R328 determine the r atio of currents in pin 11 and pin 12,
hence the ratio of currents in transistors connected to pins
6 and 8 to the current in transistors connected to pins 5
and 9. Varying this ratio controls the gain of U3101• At a ll
sensitivities other than 5 mV/div, pins 11 and 12 of U350
are shorted together by S95. Thus half the signal current in
U350 is lost through R367 and R368. In 5 mV/div, S95
contacts open, causing all of the signal current to flow in
the transistors connected to pins 5 and 9, doubling the gain
1
Gi l bert , Barrie, A New Wide- Band Amplifier Technique, IEEE
Journal of Solid State Circuits , Vol SC,3 number 4, December,
1968, P353.
3-1

Circuit Oe.scription- 485 / R485 Service
of U350. Other S95 contacts (shown on schematic 4) close
to maintain the voltage at outer collectors pins 5 and 9 of
U350. R355, R356. and R357 are low frequency (t her ma l}
transient response compensations. The CH 2 gain control
R3 58 is used to allow the CH 2 gain control (front-panel)
to be centered in its range.
SIGNAL CHANNEL SWITCH
Signal from U 350 is connected to pins 13 and 1 of U4 30
and exits U430 at pins 16 and 14. The signal then continues
on to and is terminated by the trigger channel switch U530,
diminished slightly in bandwidth by the energy extracted
by U430.
A push-pull pos1t1on control signal is injected between
U430 and U 53 0 through R376 and R386.
If no current flows through 0436, pin 12 is 0.3 V higher
than pin 11 and U430 is on. Under this condition, the
amplified signal leaves pins 5 and 9 on 100 n EC board
transmission lines, joins with the signal from channel 1 and
enters the A Ext Trigger relay K410 on 50 n EC board
transmission lines.
In struments without the A Ext Trigger op tion contain
jumper wires in place of the relay. The A Ext Trigger signal
is injected by the relay at this location, which is considered
to be the interface between the preamplifier and the main
vertical amplifier. A A LC network consisting of C407,
L409, R40 7, etc. provides some boost to compensate for
delay li ne losses at high frequencies.
The signal ne xt passes into the delay line DL410 which
delays the vertical signal 75 ns so that the sweep may start
before presentation of the triggering signal.
INTERNAL TRIGGER AMPLIFIER
Signals looped through U430 continue to trigger channel
switch U530 and are terminated in R528 and R529 which
are the collector loads tor U350. If no current flows in
0538. voltage divider R534 and R535 holds pin 12 of
U530 above pin 11 and the CH 2 trigger signal amplified in
U530 appears between pins 5 and 9 of U530. Trigger
channel switch U530 is turned off when 0538 conducts
4 mA, pulling pin 12 down to 9.8 V (0.3 V below pin 11 }.
Signal current in this case is s horted out by the connection
between pins 6 and 8. In either case, the total current in
U530 is unchanged so that the voltage on pins 5 and 9 of
U510 remains unchanged at + 12 V.
0544 and 0546 provide small additional gain for the
trigger signal. RT551 temperature c omp ensates the gain of
3-2
stages U310 through 0564. 0552 and 0556 select the
bandwidth of the trigger signal.
In the full bandwidth mode 0556 is on and 0552 is off.
Filter L559, R559, R557, and C557 provides a constant
impedance at all frequencies as the co ll ector load of 0556
and thus fu ll bandwidth. In the 20 MHz mode 0552 is on,
0556 is off, and high frequencies are attenuated by C557.
Since the bandwidth filter in the vertical amplifier is a
two-pole filter, the 3 dB point of the trigger's single pole
filter is slightly less than 20 MHz. The low frequency phase
shift of the two filters is identical, however, so that phase
match may occur in X-Y operation of the scope.
Signals at the collector of 0556 are buffered by emitter
follower 0564 and sent to A and B trigger amplifiers via
J568 and J566 respectively. CR562 matches the base
emitter junction of 0564, and R560 is adjusted so that the
zero signal voltage at O56 4' s emitter is zero. R562 pulls
away the collector current of 0556 or 0552.
0572 and 0576 buffer the trigger signal, which becomes
the X signal in X-Y mode . C572 is part of the filter which
matches the delay of the vertical delay line DL410.
Trace Separation
Trace separation circuitry injects a positioning signal at
the main vertical interface during the operation of B sweep
in the AL Ternat e sweep mode.
0 44 0, 0456, 0444, and 0454 provide the push-pu ll
trace separation signal through R440 and R456. R458 and
C458 ensure that the output impedance of the trace
separati on circuitry is 100 n at all frequencies.
MAIN VERTICAL AMPLIFIER
The signal received from delay line D l410 is terminated
and T coil peaked by the inductance of pins 1, 13, 14, and
16 of U620. The required add it ional inductance L621 and
L625 is achieved in the leads to pins 16 and 14 which are
lengths of run on the etched circuit board. This inductance
plus C621 and C625, made from 3 layers of etched cir cuit
board, and R621 and R625 form the forward termination
of the delay line. The same method of termination and
peaking is used in each stage using the 151- 0078 integrated
circuit.1 The network attached to pins 2 and 3 of U620,
provides delay tine and thermal transi ent response compen-
sation. The gain of the main vertical amplifier is adjusted by
R629. Vertical amplifier gain is temperature-compensated
by RT644.
1
Addis , John " Thr ee Technolog ies On One Chip Make A Broadband
Amplifier", Electron i cs, June 5, 1972 , Pg. 103.

The network connected between U650 and U 660 is the
bandwidth limiter network. The network provides a con·
stant impedance of 50 n per side at all frequenc ies looking
from pins 4 and 10 of U660. In the full bandwidth mode,
signal from pins 5 and 9 of U650 loops through U660 and
is terminated in the bandwidth limit network. In the
20 MHz mode, the signa l is obtained from pins 6 and 8 of
U650. In passing through the bandwidth limit network
signals above 20 MHz are attenuated at 12 dB /octave.
U660 is an FT doubler configuration with the input
T coil peaked. Bias for the inner set of bases is set by R672
an d R673. The output transistors are high voltage devices
which drive the CRT's distributed deflection structure.
In the event of a loss of a CRT termination resistor, the
long tail current through R657 pulls pins 2, 8, and 3 of
U660 down. When the +27 V supply goes below 25 V,
0686 turns on, turning on 0688 which shorts the 25 V
supply. The toss of th e +25 V supply will shut down the
power supply inverter. See inverter current limiting.
SCALE FACTOR READOUT
Scale factor readout control circuitry is in U80. With a
1X probe or with an non-readout coded connector con-
nected to the input connector code ring surrounding J1 , pin
11 of U80 is connected to +5 V through R81 . The voltage
at pin 11 is sensed by U80 and pin 10 is pulled down,
lighting the X1 light emitting diode ( LED).CR99.11 k!1 to
ground from the code ring shuts off CR99, and turns on
CR98, the XlO LED. A 6.8 k!t from the code ring to
ground will shut off the XlO LED and light CR97, the
X100 LED. A short circuit on the code ring provides trace
ID which pulls down pin 7 of U80, shifts the trace upward
one-fourth of a division, and shuts off the scale factor light.
The trace ID signal goes to R289 on CH 1 and R389 on
CH 2 to provide trace shift in the vertical pre-amplifiers.
VERTICAL MODE CONTROL
U1535B controls the vertical logic (diagram 3) via two
control leads from pins 8 and 9. These leads also are
connected via 01590 and 01594 to the trigger logic
(diagram 4) when the trigger is NORM. The trigger logic is
independent of Ul 535B when CH 1 or CH 2 triggers are
called up.
U1535B is contro lled by the mode switch in CH 1,
CH 2, ADD, or X-Y. In the ALT or CHOP mode, the !C's
control the input to pin 7 of U1535B to cause it to either
alternate on command from A GATE or to CHOP. When
the HOR IZ is in ALT, and the vertical in ALT, Ul 535B
changes sta te only every other A GATE. No te that A GATE
is the signal that activates Ul 535 in ALT and the signal
®
Circuit Oe sc ription- 485/R485 Service
from Ul 5308 pin 6 only allows every other A GATE
t hr ough. U1 535A output is A GATE 2, and Ul 535B is A
GATE 4.
In the CHOP mode, Ul 585 is on and Ul 535B changes
state every time Ul 585 makes an output. While Ul 585 is
making an output a signal from Ul 585 pin 4 blanks to
prevent displaying the switching from CH 1 and CH 2 and
back.
ZAXIS
U1560 output drives the Z AXIS amplifier. U1560 is
controlled by the A and B GATES, the A-B control via pin
15, the INTEN sity controls and the EXT Z AXIS.
The circuit consisting of 01566 and 01568 disconnects
the B INTENSITY contro l during X·Y or when A=l , 2, or
5 ns.
A TRIGGER AMPLIFIER
The Source Switch SW700 selec ts one of the four modes
which the 485 wi ll trigger on: INT, LINE , EXT, or EXT +
10. Signals above approximately 1 MHz, except in HF REJ
are coupled through C705. R705 and R7 09 form a 1 Mn
input resistance and a loss pad to compensate for the loss
across C705, matching high frequency and low frequency
gains. R708 protects O712A input by limiting current when
CR711 or O712A is forward biased. 0712A and 07128
form a source follower with the source voltage very close to
zero. The source follower drives 0716, an emit ter fo llow er,
which drives U730. The balun coil T719 produces a
differential signal. U730, U738, and U740 are cascode
amplifiers. Th e slope switch SW 720, switches the collectors
of U740 to give selection of the triggering slope.
A EXT TRIGGER IDENTIFY
The A EXT TRIG IDENTIFY function is driven by the
emitters of U730; this allows U830 to be coupled to the
trigger signal and the leve l control. The center line crossing
point of the A EXT TRIG signal corresponds to thetrigger
point of the sweep for timing information.
When the EXT TR IGGER IDENTIFY switch is pushed,
U830 is turned on and its collectors are connected to the
vertical delay tine via relay K410. VR838 and VR839
provide DC level shift.
The cables between J842 and J843 and relay K 10 have a
time delay so that the EXT trigger signal will be displayed
with the same time position as signals arriving through CH 1
or CH 2 input.
3.3

Circuit Description-485/R485 Service
A TRIGGER GENERATOR
The trigger amplifier drives a Schmitt Trigg er circuit
based around CR751 and a constant resistance load. This
circuit provides a standardized output pulse that is time
related to the trigger event. This standardized pulse and a
holdoff signal drive a two tunnel diode circuit to provide
stable triggering from DC to at least 350 MHz with very low
trigger jitter.
CR762 is the arming tunne l diode and CR772 is the
output tunnel diode. After CR762 is fully armed and
CR772 is partially armed (at the end of holdoff), a pulse
from CR751 causes CR762 to go to its high state. Th is
increases the current through R764 to fully arm CR772,
which goes to its high state when the same pulse that fir ed
CR762 is received th rough the short delay line. The output
of CR772 drives differential pair 0792 and 0794. When
CR772 is in its high state pin 1 of U780 is high, turning on
the light DS781 (TRIG'D). 0792 provides the A GATE
through emitter fo ll ower 0810 . The outpu t of 0794
coup les to a differential pair 0802 and 0804, which
provide the sweep gates.
When the sweep is completed, a posi ti ve signal from A
sweep turns on 0816 and 0822 to provide a signal to pin
16 if U780. This initiates the holdoff portion of U 780 and
pin 17 goes positive. Pin 17 stays positive as dete rmined by
timing R' s and C's on the timing switch to pin 8. The
holdoff signal on pin 17 of U780 drives 0768 and 0778 .
0768 and 0778 gate the current to CR762 and CR772.
When 0768 and 0778 are ott, CR762 and CR772 are
receiving the appropriate current as set by R765 (A arming
T.D.) and R775 (A output T.D.). When 0768 and 0778 are
on they reset CR762 and CR772 to their low states.
In AUTO TRIG pin 19 of U780 is grounded. The trigger
signals must recur at least every 50 ms, which is the lowest
rate the circuit will provide a triggered sweep in AU TO
MODE. The timing of the AUTO MODE is determined by
the time constant of R787 and C787.
In SINGLE SWEE P mode +5.5 Vis applied to pin 12 of
U780. There wi ll be only one sweep for each time U780 is
a rm ed by pushing the RESET switch. The sweep will fire
when a trigger signal is received while or after the RESET
switch is depressed. The READY light on pin 11 of U780
indicates when the sweep is armed.
B TRIGGER GENERATOR
Is similar to A Trigger Generator ex cept it has RUNS
AFTER DELAY TIME mode that disconnects the trigger
amplifier. In addition, it uses A Trigger Gate and delay
pickoff gate as hold-off.
3-4
In the tr igge rab le mode, the BTrigger Generator triggers
only after receiving both the delay pickoff and A Gate
signals. Delay pickoff gate drives comparator 01092 and
01096 . Both A Gate and delay pickoff gate are required to
drive 01082 . The output of 01074 provides arming current
for CR1062 and CR1 10 4. When the triggering signal causes
CR1 052 to go to its high state, CR1062 is properly armed,
and will fire arming CR 110 4, which fires approximately
1 .5 ns after CR1062.
In B RUNS AFTER DELAY TIME mode, the trigger
amp li fier is turned off via R1038 and enough current is
flowing in the base of 01068 so that it is in saturation. This
saturation routes enough current to CRl 104 to turn it on
when A Gate and delay pick off gate arrive.
In both cases when CRl 104 goes to its high state,
comparator 0 1106 and 01110 changes state giving a B
GATE out t hr u 01114. 01106 is connected to comparator
0 11 21 and 01124 which changes state, giving plus and
minus sweep gate out.
In A 1, 2, and 5 ns, B is in BRUNS AFTER DELAY
TIME. In addition in 1 and 2 ns the voltage to which Cl 121
charges is varied by th e HORIZONTAL POSITION control.
This gives a time position to these two sweep speeds when
using the HOR IZONTAL POSITI ON c ontrol.
A and B SWEEPS
A and B sweep generators each produce, upo n receipt of
a gat e, a negative going sweep of 1.0 V /d iv of horizontal
excursi on, starting at + 13 V.
In A Sweep, 0884 and 0888 are the miller amp lifier.
Timing resistors R873 and R1409 to R1422 return to
+50 V in calibrated settings. The values of the timing
resistors and capacitors C877 to C882, C1404 and C14 05,
at various sweep speeds may be determined on the Timing
Switch and Gen erato r schematics. 0892 compares the
sweep output to + 13 V and sends th e error signal to the
miller input via R866 and 0854. Receipt of a + gate at
TP851 turns off 085 4, allowing the sweep to run. CR867
must not conduct during baseline, so 0866 sinks the higher
timing currents. 0934 turns on at the end of the sweep,
producing a + going stop pulse th at terminates the sweep
gate. 0856 and 0858 feed a current to the miller input at
the end of the gate to prevent large negat ive voltages and
long recovery times at l ow timing currents. R863 affects
linearity at 10 and 20 ns/div.
The Delay Compar ator 0902 enables B Sweep when the
sweep voltage becomes less than th e voltage on the Delay
Time position control, where U910 is a voltage follower.

0908 disables B Sw eep in A HORIZ DISPLAY mode and
0914 introduces an offset at 10 and 20 ns/div. Switch A9
opens when A Sweep speed is 1, 2, or 5 ns/div to start B
Sweep with minimum delay, since the B Sweep Generator
produces these speeds regardle ss of the HORIZ DISPLAY
mode.
B Sweep generator is similar to A except that the
maximum output rate is 5 times faster. The sequence of
timing components is different from A Sweep. 01238
prevents large positive voltages that would occur at the
miller input after the end of the sweep but before the end
of the gate.
For A Sweep speed settings of 10 ns/div or slower, A
HORIZ DISPLAY mode displays A Sweep. B HORIZ
DISPLAY mode displays B, ALT, INTEN, and INTEN (A)
function. However, when A Sweep speed is set at 1, 2, or
5 ns/div th e Hori zonta l system displays B Swe ep which has
been gated on by A trigger. Switch A9 is open so that the
Delay Time Position control is effect ively set to zero. At A
= 5 ns/div, the displayed BSweep is po si tioned ho rizontally
in the amplifier. At A = 1 or 2 ns/div, the POSITION
contr ol is disconnected from th e Horizontal Amplifier via
switches B19 and B20. The POSITION control is connected
to a variable delay circuit 01102 which time-positions B
Gate for about 30 ns after A Gate.
HORIZONT AL AMPLIFIER
The A sweep or B sweep may be selected by saturating
01312 or 01318 respectively. This is done by the
horizontal control logic level at N4 . If N4 is below - 5 V,
01336 is off and 0 1 338 saturates. This allows the node
R1 313, R1314 to go up and turns off 0 1 318 and saturates
01312. Th e output of A sweep generator has been selected.
01338 being saturated also shunts to ground any signal
from Bsweep generator that might be present in ALTernate
mode. If N4 is - 3 V, B sweep is selected as 01336
sat urat es, turning off 01338 and pulling down on R1314,
saturating 01318 and turning 01312 off. CR1311 will
shunt any signal from A sweep.
A +1 V at N4 will turn 0 1 342 on which turns off
0 1 358, disconnecting A and B sweeps and saturating
01356. sel ect ing the X signal for X-Y.
In A = 1, 2, or 5 ns, 818 closes and 0133 1 turns on,
saturating 0 1 322, a 2X magnifier. To provide offset to
enable vi ewing at sweep start, in 5 ns 822 closes and offs et
through R1 327 is provided. In 1 and 2 ns, the base of
01328 is moved and a current from 01328 through 01331
and the base collector of 01332 is inserted to provide
offset.
Circuit Oescri pti on- 48 5/ R4 85 Service
01362 and 01364 compose a HI gain amplifier. The
feedback R is R1364 and R1366. Th e input resistance in B
sweep is R1321 and R1 322. If A sweep is selected the input
resistance is R 1307 and R1 308.
By selecting B sweep and adjusting R1366, the hori·
zontal gain is set. Then by selecting A sweep and adjusting
R1308, A sweep may be calibrated. Both adjustments are
done in 0.1 ms/div. To get A and B swe ep to start at the
same point on screen, R1325 (B REGISTER) provides
some offset current for positioning B sweep relative to A
sweep. This is done in ALT horizontal mode. 01378 and
R1368 provide a constant current for th e operational
amplifier 01362, 0 1 364. 01366 is saturated in Beam
Finder by S600B. This cuts the feedback resistor value by
2/3 and Rf /RI is reduced. Cl 364 provides linearity control
for 1, 2, and 5 ns/div.
01372 and 0 1 374 are a paraphase amplifier to provide a
differential signal to the horizontal amplifier. Cl 372,
C1374, R1372, and R1374 provides thermal compensation
for 0 1 372 and 01374. Since the horizontal is symmetrical,
we wi ll deal with one half only. 01172 provides isolation
between the CRT capacitance and the input amplifier
01 1 54. 01172 and 01174 provide the current path to
drive the deflection plat e. 01192 is 'an emitter follower to
provide feedback to 01154 . By using active feedback the
actual feedback resistance may be lowered without sacrific•
ing gain. This is accomplished by utilizing the impedance of
01192 , emitter to base, and the divider circuit of R1177
and R 1178. CR 1156 provides a -5 V reference for O 1154
and CR1152 . CR1153 limits the voltage swing to keep
either half of the horizontal from saturating. This allows
the horizontal to be very linear.
HORIZONTALCONTROL
This circuit is activated by the HOR 12 DISPL AY
contro ls. Several output signals are derived; B disable,
horizontal control, A-8 control autofocus, trace separation
and vertical control drive.
The basic circuit consists of Ul 535A which is contro lled
by the HORIZ DISPLAY. The HORIZ DISPLAY switch is
overridden when B sweep is used in A = 1, 2, or 5 ns or is
X·Y. A truth table is shown on the diagram 12.
The main function of Ul 535 is to provide a HOR IZ
CONTROL signal to the horizontal B preamplifier. With the
X-Y control of 01520 (which saturates in X-Y), this signal
on pin N4 has 3 levels. In the ALT mode, Ul 535 switches
from one state to another each time the A GATE goes
negative. U1530C inverts the A GATE to get the positive
edge required by Ul 535A. (It is important to maintain
correct timing with the sweep control since switching must
3-5

Circuit D esc ription- 485 /R485 Service
occur during holdoff.) Pin Sot U1535A alternates from HI
to LO and the sweep switches from A to 8 and back again.
When 8 is called up and pin 5 is HI, the Z AXIS IC will be
in the 8 mode via pin 15 si gnal an d the 8 intensity control
will function and Autofocus control is also provided. Also,
the trace separation signal will be LO, causing the trace
separation contro l to function. Th is is via control of
U1 5308. All inputs must be HI to get LO outputs, and this
only occurs in ALT when B is ca ll ed up. The output of
U15308 also drives the vertical logic when the HOR 12
DISPLAY is in ALT. 8 disable is controlled by A, the X-Y
signal, and switch SWA2 (which is closed when A = 1, 2, or
5 ns).
POWER INVERTER / REGULATOR
General
The P ower Inverter/Regulator circuit provides the opera·
ting power for this instrument from a line voltage source or
DC voltage source. This circuit al so includes th e Li ne
Voltage Selector switch to allow for selection of a 115 V or
230 V nominal operating voltage. Fig. 3-1 shows a block
diagram of the Power Inverter/Regulator circuit. A sche·
matic is shown on diagram 14 at the rear of this manual.
Line Filt er
The purpose of the Line Filter is to prevent the
instrument from injecting power su pply frequency inter-
ference into the power line, or power-line interference from
entering the instrument. L1812 and L1813 provide both
common-mode and differential filt ering. R1812 and R1813
are damping resistors. Cl 812 and C1813 are common-mode
tilters and C1814 is a differential fi l ter. R18 11 discharges
C1814 when the power switch is off.
(
F1801
Line
In put Voltage
Line
Filter
l ine Input
CR1821 ,
C 1822 , C1823
Line Trigger
Start N etwork
VR1831 , C1829
Line Inp ut Circu it
Thermal cutout S1802 provides therma l prot ection for
this instrument . If the temperature exceeds a safe operating
level, S1802 opens to interrup t the applied power. When
the temperature returns to a safe operating level, S1802
automat ically closes to re-apply the power.
CR1821 con tains the main power rectifiers for the Line
Input circuit. C 18 22 and C1823 are the line-storage
capacitors. With S1803 in the 11 5 V position, the circuit
acts as a full-wave vo lt age doub l er so tha t the voltage across
the series combination of C1 822 and C1823 will be the
peak -t o-peak value of the line voltage. In the 230 V
position, CR1821 acts as a ful l- wave bridge rectifier.
Therefore the voltage developed across C1822 and C1 823
wi ll be approximately the same for eit h er 11 5 V or 230 V
operation .
RT1821 and RT1822 are thermistors which limit the
charging currents during turn on. When the POWER switch
is turned oft, the Li ne Stop circuit stops the Inverter and
C1822 and C1823 discharge thru R1822 and R1 823.
I WARNING I
Because the discharge is slow, dangerous potentials
will exist across capacitors C1822, C1823, and other
connected components f or several minutes after the
POWER switch is turned off. The presence of voltage
in the circuit is indicated by relaxation oscillator
R1824, C7824, and DS1824. Neon bulb OS7824
blinks un til the potential drops to approximately
100 V.
Over Voltage
St op
01840, 01846
Inverter
01834. 01844
Regulat or &
Stop Monostable
01900, 01902
Regula tor Amplifier
/Ma in Power Trensf or mer
f T1960
3 kV p.p
r To H .V . C ir cu its
1-- --+- +1 80
l ow Volt a get----+- +120
Rec tifi ers
Ph ase Tran sfor mer
T1848
..,_ _ _ +59.4
1-- --- +25
.._--+- • 15
1----+- t 5.5
l in e S to p I-+----'
& P ro t ec ti on --- --- +59 .4
U1910 Balance Nod e
Fig . 3- 1. B loc k diagr am of power inve r ter / r egulator circuit .
3-6
REV. B, AUG. 1975

DS1801 and DS 1 802 are line voltage transient pro-
tectors. With S1 803 in the 11 5 V position. only DS 1801 is
connected across the line. If a peak voltage surge in excess
of approximately 230 V is present on the line, DS1801 will
break down and conduct sufficient current to open the line
fuse F1801. In the 230 V position, DS1801 and DS1802
are in series across the line to protect against voltage surges
exceeding 460 V.
Transformer Tl 801 provides a sample of the line voltage
for triggering at line frequencies. It also provides a signal to
the Line Stop circuit to indicate the presence of line voltage
at the input to this circuit. T1825, C1825, and Cl 827
provide common-mode filtering. Cl 826 and L1 825 act as a
differential filter.
Sta rt Network
Resistive divider Rl 828 and R1829 is connected be•
tween the input line and the negative side of Cl 823. When
the line voltage goes positive, Cl 829 charges. At the same
time CR1842 conducts, charging C1835, and CR1843
conducts to charge Cl 848. When the voltage on C1829
reaches approximately 3J V, VR1831 conducts, discharging
C1829 thru the base of 0 1 844. As 01844 turns on, C1835
discharges thru L 1835 to start the Inverter. After operation
has begun, CR 1842 discharges Cl 829 with each cycle of
the Inverter. This disables the start network.
Inverter
Refer to the simplified schematic shown in Fig. 3-2.
Once the Inverter has been started by the Start Network, the
Inverter is selt-oscillating. Feedback necessary for oscilla-
tion is provided by base-drive transformer T1 831. The
series-resonant circuit, consisting of L1835 and C1835, has
+ ------ - -------~
OCINPUT
VOLTAGE
0 1 834
Circuit D esc ription -485/ R 485 Se rv ice
a nominal resonant frequency of about 25 kilohertz. To
provide regulation of the voltages induced in the secondary
circuit, the action of regulator transistor 01900 varies the
frequency of oscillation on the low side of resonance by
holding both 01834 and 01844 off for a time during each
half cycle as determined by the Regulator circuit (see
Inverter Regulator for a more detailed discussion of regula-
tion).
Transistors 0 1 834 and 01844 are a switching pair,
where only one transistor can conduct at a time. The
direction of current flow in the feedback winding of T1831
determines which transistor will conduct. Transistors
0 1 834 and 01844 change states every half cycle. The
switching action provides a square-wave voltage at the
emitter of 01834, which has a peak-to-peak voltage about
equal to the DC voltage from the Line Input circuit. This
square-wave voltage supplies the drive necessary to main-
tain oscillation in the resonant circuit. When both 01834
and 01844 are being held off by 0 1900, resonant circuit
current flows through CR1834 or CR1844. The resonant
circuit current drives the primary of the power transformer
T1960 and thus supplies power to the Secondary circuit.
In normal operation, the sequence of events during one
cycle of operation is as follows:
1. Assume the current in the resonant circuit is at 0
ampere and beginning to increase in the direction to cause
conduction in CR1834. At the time the current reaches 0
ampere, regulator transistor 01900 is turned on by the
Inverter Control circuit. The Regulator transistor holds
both 0 1 834 and 01844 off for a controlled amount of
time. During this time, resonant circuit current flows
through CR1834.
RECTIF I ER
BRIDGE
c,s
3s
T196 EO 10 J TO
-----1------------
CR1844
0 1 900
Fig. 3- 2. Simplified schematic of Inverter.
REV . C, AUG. 1975
INVERTER ..._ __
CON TROL
1193 -06
3-7