Farnell 72-6800 User manual

20MHz Dual Trace Oscilloscope
MODEL: 72-6800
8272-68000MC1

CONTENTS PAGE
1. GENERAL……………………........................................…..............................…………….
1-1.Description………………………………………………………………………………………………….
1-2.Feature………………………………………………………………………………………………………
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2. TECHNICAL SPECIFICATIONS.……………………………………………………….
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3. PRECAUTIONS BEFORE OPERATING THE OSCILLOSCOPE…...….…………….
3-1.Unpacking the Oscilloscope….……………………………………………….……………………………
3-2.Checking the Line Voltage…………………………………………………………………………………
3-3.Environment………………………………………………………………………………………………..
3-4.Equipment Installation and Operation……………………………………………………………………
3-5.CRT Intensity……………………………………………………………………………………………….
3-6.Withstanding Voltage of Input Terminals……………………………………………………………….
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4 OPERATION METHOD…………………………………………………………………..
4-1. Introduction of Front Panel………………………………………………………………………………
4-2. Introduction of Rear Panel………………………………………………………………………………
4-3.Basic Operation-Single channel operation…………………………………………………………….…
4-4.Dual-channel Operation……………………………………………………………………………………
4-5.ADD Operation……………………………………………………………………………………………..
4-6.Triggering…………………………………………………………………………………………………..
4-7.TIME/DIV control………………………………………………………………………………………..
4-8.Sweep Magnification………………………………………………………………………………………..
4-9.X-Y Operation………………………………………………………………………………………………
4-10.Calibration of Probe……………………………………………………………………………………..
4-11.DC BAL Adjustments …………………………………………………………………………………
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16
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5. MAINTENANCE……………………………………………………………………………
5-1.Fuse Replacement…………………………………………………………………………………………..
5-2.Line Voltage Conversion…….……………………………………………………………………………
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5-3.Cleaning……………………………………………………………………………………………………..
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6. BLOCK DIAGRAM………………………………………………………………………...
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SAFETY TERMS AND SYMBOLS
These terms may appear in this manual or on the product:
WARNING . Warning statements identify condition or practices that
Could result in injury or loss of life .
CAUTION . Caution statements identify conditions or practices that
could result in damage to this product or other property.
The following symbols may appear in this manual or on the product:
DANGER ATTENTION Protective Earth(ground)
High Voltage refer to Manual Conductor Terminal
Terminal

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FOR UNITED KINGDOM ONLY
NOTE As the colours of the wires in main leads may not correspond with the colours
This lead/appliance must only marking identified in your plug/appliance, proceed as follows:
be wired by competent persons
WARNING The wire which is coloured Green & Yellow must be connected to the Earth terminal
THIS APPLIANCE MUST BE marked with the letter E or by the earth symbol or coloured Green or Green &
EARTHED Yellow.
The wire which is coloured Blue must be connected to the terminal which is marked
IMPORTANT with the letter N or coloured Blue or Black.
The wires in this lead are
coloured in accordance with The wire which is coloured Brown must be connected to the terminal marked with the
the following code: letter L or P or coloured Brown or Red.
Green/ If in doubt, consult the instructions provided with the equipment or contact the supplier.
Yellow: Earth
Blue: Neutral This cable/appliance should be protected by a suitably rated and approved HBC mains
Brown: Live(Phase) fuse : refer to the rating information on the equipment and/or user instructions for details.
As a guide, cable of 0.75mm²should be protected by a 3A or 5A fuse. Larger
conductors would normally require 13A types, depending on the connection method used.
Any moulded mains connector that requires removal/replacement must be destroyed by
removal of any fuse & fuse carrier and disposed immediately, as a plug with bared wires
is hazardous if a engaged in live socket. Any re-wiring must be carried out in accordance
with the information detailed on this label.

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1. GENERAL
1.1 Description
The 72-6800 oscilloscope is a portable-type, dual-channel oscilloscope with a bandwidth of DC to 20MHz, and
maximum sensitivity of 1mV/DIV. The time base provides a maximum sweep time of 0.2uS/DIV. When magnified by
10 ， the sweep speed is 100nS/DIV. The oscilloscope uses a 6-inch rectangular type cathode-ray tube with red internal
graticule.
This oscilloscope is sturdy, easy to operate and exhibits high operational reliability.
1.2 Features
1) High intensity CRT with high acceleration voltage:
The CRT is a high beam transmission ， high intensity type with a high acceleration voltage of 2kV. It displays clear readable
traces even at high sweep speeds.
2) Wide bandwidth and sensitivity:
In addition to wide bandwidth, DC-20MHz (-3dB), this instrument provides high sensitivity of 5mV/DIV (1mV/DIV at ×
5 MAG). A 20MHz frequency is obtained with improved triggering synchronization.
3) Alternate triggering:
Even an observation of two waveforms of different frequencies the waveforms of the each channel is stably triggered.
4) TV sync triggering:
The oscilloscope has a sync separator circuit for triggering of TV-V and TV-H signals .
5) CH1 Output:
Terminated 50Ωoutput of channel 1 signal available on rear panel for driving frequency counter or other instruments.
6) Z-Axis Input:
Intensity modulation capability permits time or frequency markers to be added. Trace blank with positive signal, TTL
compatible.
7) X-Y operation:
Set the switch to X-Y .Then the instrument works as an X-Y oscilloscope. CH1 can be applied as horizontal deflection
(X-axis) while CH2 provides vertical deflection (Y-axis).

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2. TECHNICAL SPECIFICATIONS
MODEL
SPECIFICATIONS
72-6800 20MHz OSCILLOSCOPE
1.OSCILLOSCOPE
Sensitivity 5mV
～ 5V/DIV, 10 steps in 1-2-5 sequence.
Sensitivity accuracy ≤3% ( × 5 MAG : ≤5%).
Vernier vertical sensitivity To 1/2.5 or less of panel-indicated value.
DC ～ 20MHz ( × 5MAG: DC ～ 7MHz).
Frequency bandwidth AC coupling: Low limit frequency of 10Hz.
(With reference to 100kHz, 8DIV. Frequency response with -3dB).
Rise time Approx. 17.5nS (×5 MAG: Approx. 50nS).
Input impedance Approx. 1M ohm // Approx. 25pF.
Square wave
characteristics
Overshoot : ≤5% ( At 10mV/DIV range).
Other distortions and other ranges: 5% added to the above value.
DC balance shift Adjustable.on panel
Linearity <
± 0.1DIV of amplitude change when waveform of 2 DIV at graticule center is moved vertically.
Vertical modes
CH1 : CH1 single channel.
CH2 : CH2 single channel.
DUAL : CH1 and CH2 are displayed. ALT or CHOP selectable at any sweep rate.
ADD : CH1 + CH2 algebraic addition.
Chopping repetition
frequency Approx. 250kHz.
Input coupling AC, GND, DC.
Maximum input voltage
300Vpeak (AC: frequency 1kHz or lower).
When set probe switch at 1: 1, the maximum effective readout is 40Vpp (14Vrms at Sine wave),or
set probe switch at 10: 1, the maximum effective readout is 400Vpp(140Vrms at sine wave).
Common mode rejection
ratio 50:1 or better at 50kHz sinusoidal wave. (When sensitivities of CH1 and CH2 are set equally).
Isolation between channels
(At 5mV/DIV range)
>1000:1 at 50kHz.
>30:1 at 20MHz.
VERTICAL
AXIS
CH1 signal output At least 20 mV/div into a 50
ohm termination, Bandwidth is 50Hz to at least.5MHz

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MODEL
SPECIFICATIONS
72-6800 20MHz OSCILLOSOPE
Triggering source
CH1, CH2, LINE, EXT (CH1 and CH2 can be selected only when the vertical mode is DUAL or
ADD .
In ALT mode, if the TRIG. ALT switch is pushed in, it can be use for alternate triggering of two
different source.
Coupling AC: 20Hz to full bandwidth.
Slope + / -.
Sensitivity
20Hz ～ 2MHz : 0.5 div, TRIG-ALT:2 div, EXT : 200mV.
2 ～ 20MHz : 1.5 div, TRIG-ALT:3 div, EXT : 800mV.
TV : Sync pulse more than 1 div (EXT: 1V).
Triggering modes AUTO : Sweeps run in the free mode when no triggering input signal is applied.
(Applicable for repetitive signals of frequency 25Hz or over.).
NORM : When no triggering signal is applied, the trace is in the ready state and not displayed.
TV-V : This setting is used when observing the entire vertical picture of television signal.
TV-H : This setting is used when observing the entire horizontal picture of television signal.
(Both TV-V and TV-H synchronize only when the synchronizing signal is negative )
TRIGGERING
EXT triggering signal input
Input impedance
Max. input voltage
Approx.: 1M ohm // approx. 25Pf.
300V (DC+AC peak), AC: Frequency not higher than 1kHz.
Sweep time 0.2
μ Sec ～ 0.5 Sec/DIV, 20 steps in 1-2-5 sequence.
Sweep time accuracy
± 3%.
Vernier sweep time control ≤1/2.5 of panel-indicated value.
Sweep magnification 10 times
x10MAG sweep time
accuracy
± 5%, (20nSec ～ 50nSec are uncalibrated).
HORIZIONAL
AXIS
Linearity
± 3%, x10MAG: ± 5% (20ns and 50ns are uncalibrated).
Sensitivity Same as vertical axis (X-axis:CH1 input signal; Y-axis:CH2 input signal.).
Frequency bandwidth DC to at least 500KHz.
X-Y MODE X-Y phase difference
≤3
0
at DC ～ 50kHz.

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MODEL
SPECIFICATION
72-6800 20MHz OSCILLOSCOPE
Sensitivity 5 Vp-p (Positive-going signal decreases intensity).
Frequency bandwidth DC
～ 2MHz.
Input resistance Approx. 47K
ohm .
Z AXIS
Maximum input voltage 30V (DC+AC peak, AC frequency≤1kHz).
Waveform Positive-going square wave.
Frequency Approx. 1 kHz.
Duty ratio Within 48:52.
Output voltage 2 Vp-p
± 2%.
CALIBRATION
VOLTAGE
Outputimpedance Approx. 1 k
ohm .
Type 6-inch rectangular type, internal graticule.
Acceleration voltage Approx. 2kV.
Effective screen size 8 x 10 DIV (1 DIV = 10mm (0.39in)).
Graticule Internal
.
CRT
Trace Rotation
Provided.

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Line Power Requirements Operating Environment Accessories
Voltage :AC115V, 230V ± 15% selectable Indoor use Power cord……..…....1
Frequency : 50Hz or 60Hz Altitude up to 2000 m Instruction manual……1
Power consumption :Approx. 40VA,35W(max) Ambient temperature: Probes………………...2
To satisfy specifications : 10°to 35 ℃ (50°to 95°F)
Maximum operating ranges: 0°to 40 ℃ (32 °to 104°F)
Relative humidity: 85% RH(max.) non condensing
Installation Category II
Pollution degree 2
Mechanical Specifications Storage Temperature & Humidity
Dimensions: 310 W x 150 H x 455 D (mm) -10°to 70 ℃ , 70%RH(maximum).
Weight :Approx.8kg (17.6lbs)

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3. PRECAUTIONS BEFORE OPERATION THE OSCILLOSCOPE
3.1 Unpacking the Oscilloscope
The oscilloscope is shippied from the factory after being fully inspected and tested. Upon receiving the instrument,
immediately unpack and inspect it for any damages that might have been sustained during transportation If any sign of
damage is found, immediately notify the bearer and/or the dealer.
3.2 Checking the Line Voltage
The oscilloscope will operate on any one of the line voltage shown in the table below. by inserting the line voltage selector
plug in the corresponding position on the rear panel .Before connecting the power plug to an AC line outlet, make sure the
voltage selector is set to the correct position corresponding to the line voltage. Note the oscilloscope may be damaged if it is
connected to the wrong AC line voltage.
WARNING. To avoid electrical shock, the power cord protective
grounding conductor must be connected to ground.
When line voltage are changed ,replace the required fuses shown below:
Line voltage Range Fuse
AC 115V 97~132V T 0.63A
250V
AC 230V 195~250V T 0.315A
250V
WARNING. To avoid personal injury, disconnect the power cord

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bef o re removing the fuse holder.
3.3 Environment
The normal ambient temperature range of this instrument is 0°to 40°C (32°to 104°F). Operate of the instrument abover this
temperature range may cause damage to the circuits.
Do not use the instrument in a place where strong magnetic or electric field exists.Such fields may disturb the measurement.
3.4 Equipment Installation, and Operation
Ensure there is proper ventilation for the hole vent in the oscilloscope case.
If this equipment is used in a manner not specified by the manufacturer, the protection provided by the equipment may be
impaired.
3.5 CRT Intensity
To prevent permanent damage to the CRT phosphor, do not make the CRT trace excessively bright or leave the spot
stationary for an unreasonable long time.
3.6 Withstanding Voltages of Input Terminals
The withstanding voltages of the instrument input terminals and probe input terminals are as shown in the following table.
Do not apply voltage higher than these limits. When set probe switch at 1: 1, the maximum effective readout is 40Vp-p
(14Vrms at sine wave), When set probe switch at 10: 1, the maximum effective readout is 400Vp-p (140Vrms at sine wave).
Input terminal Maximum input voltage
CH1, CH2, inputs 300Vpeak
EXT TRIG IN input 300Vpeak
Probe inputs 600Vpeak
Z AXIS input 30Vpeak
CAUTION. To avoid instrument
damage, do
not exceed maximum input voltages.
Maximum input voltage must have frequency
less than 1 kHz.

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If an AC voltage which is superimposed on a DC voltage is applied, the maximum peak value of
CH1and CH2 input voltages must not exceed + or - 300V, so for AC voltages with a mean value of zero
volt the maximum peak to peak value is 600Vpp.
 Figure. 4-1.

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Figure. 4-2

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4.OPERATION METHOD
4-1.Introduction of Front Panel
CRT :
POWER…………………(6)
Main power switch of the instrument. When this switch is turned on , the LED (5) is also turned on.
.INTEN……………………(2)
Control the brightness of the spot or trace.
FOCUS…………………...(3)
For focusing the trace to the sharpest image.
TRACE ROTATION……..(4)
Semi-fixed potentiometer for aligning the horizontal trace in parallel with graticule lines.
FILTER………………..…(33)
Filter for ease of waveform viewing.
Vertical Axis:
CH1 (X) input-----------(8)
V ertical input terminal of CH1.When in X-Y operation, X-axis input terminal.
CH 2 (Y) input……….(20)
Vertical input terminal of CH2. When in X-Y operation,Y-axis input terminal.
AC-GND-DC…………(10)(18)
Switch for selecting connection mode between input signal and vertical amplifier.
AC AC coupling
GND Vertical amplifier input is grounded and input terminals are disconnected.
DC DC coupling
VOLTS/DIV………….(7)(22)
Select the vertical axis sensitivity ， from 5mV/DIV to 5V/DIV in 10 ranges.

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VARIABLE………(9)(21)
Fine adjustment of sensitivity, with a factor of ≥1/2.5 of the indicated value. When in the CAL position,. Sensitivity is
calibrated to indicated value .When this knob is pulled out (x5 MAG state), the amplifier sensitivity is multiplied by 5.
CH1 & CH2 DC BAL……(13)(17)
These are used for the attenuator balance adjustment. See page 20 DC BAL adjustments for the details.
56POSITION…(11)(19)
Vertical positioning control of trace or spot.
VERT MODE …….(14)
Select operation modes of CH1 and CH2 amplifiers.
CH1 :The oscilloscope operate as a single-channel instrument with CH1 alone.
CH :The oscilloscope operate as a single-channel instrument with CH2 alone.
DUAL :The oscilloscope operate as a dual-channel instrument both CH1 and CH2.
ADD :The oscilloscope displays the algebraic sum (CH1 + CH2) or difference (CH1 - CH2) of the two signals
The pushed in state of CH2 INV (16) button is for the difference(CH1-CH2).
ALT/CHOP………(12)
When this switch is released in the dual-trace mode, the channel 1 and channel 2 inputs are alternately displayed
(normally used at faster sweep speeds).
When this switch is engaged in the dual-trace mode, the channel 1 and channel 2 inputs are chopped and displayed
simultaneously. (normally used at slower sweep speeds) .
CH2 INV…………(16)
Inverte the CH2 input signal when the CH2 INV switch mode is pushed in The channel 2 input signal in ADD mode and
the channel 2 trigger signal pickoff are also inverted.
Triggering
EXT TRIG IN input terminal……..(24)
Input terminal is used for external triggering signal. To use this terminal, set SOURCE switch (23) to the EXT position.

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SOURCE……….(23)
Select the internal triggering source signal, and the EXT TRIG IN input signal.
CH1 : When the VERT MODE switch(14) is set in the DUAL or ADD state ,select CH1 for the internal triggering
source signal.
CH2 : When the VERT MODE switch(14) is set in the DUAL or ADD state ,select CH2 for the internal triggering
source signal.
TRIG.ALT(27) : When the VERT MODE switch(14) is set in the DUAL or ADD state ,and the SOURCE switch (23) is
selected at CHI or CH2,with the engagement of the TRIG.ALT switch (27),it will alternately select CH1&CH2
for the internal triggering source signal.
LINE :TO select the AC power line frequency signal as the triggering signal.
EXT :The external signal applied through EXT TRIG IN input terminal (24)is used for the external triggering
source signal.
SLOPE…………..(26)
Select the triggering slope .
“+” : Triggering occurs when the triggering signal crosses the triggering level in positive-going direction.
“-” : Triggering occurs when the triggering signal crosses the triggering level in positive-going direction.
LEVEL………….(28)
To display a synchronized stationary waveform and set a start point for the waveform.
Toward “+” : The triggering level moves upward on the display waveform.
Toward “-” : The triggering level moves downward on the display waveform.
TRIGGER MODE..(25)
Select the desired trigger mode .
AUTO :When no triggering signal is applied or when triggering signal frequency is less than 25Hz, sweep runs in the
free run mode.
NORM :When no triggering signal is applied , sweep is in a ready state and the trace is blanked out .Used primarily
for observation of signal ≤25 HZ .
TV-V :This setting is used when observing the entire vertical picture of television signal.
TV-H :This setting is used when observing the entire horizontal picture of television signal.

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(Both TV-V and TV-H synchronize only when the synchronizing signal is negative.)
Time Base:
TIME/DIV……….(29)
Sweep time ranges are available in 20 steps from 0.2 us/div to 0.5 s/div.
X-Y : This position is used when using the instrument as an X-Y oscilloscope.
SWP.VAR………..(30)
Vernier control of sweep time.This control works as CAL and the sweep time is calibrated to the value indicated by
TIME/DIV. TIME/DIV of sweep can be varied continuously when shaft is out of CAL position. Then the control is
rotated in the direction of arrow to the full,the CAL state is produced and the sweep time is calibrated to the value
indicated by TIME/DIV. Counterclockwise rotation the full delays the sweep by 2.5 time or more.
34POSITION…..(32)
Horizontal positioning control of the trace or spot.
× 10 MAG…..…(31)
When the button is pushed in,a magnification of 10 occurs.
Others
CAL……………..(1)
This terminal delivers the calibration voltage of 2 Vp-p, 1kHz, positive square wave.
GND…………….(15)
Ground terminal of oscilloscope mainframe.
4-2.Introduction of Rear Panel
Z AXIS INPUT………..…(34)

15
Input terminal for external intensity modulation signal.
CH1 SIGNAL OUTPUT….(35)
Delivers the CH1 signal with a voltage of approximately 20mVper 1 DIV into a 50 -ohm termination.Suitable for frequency
counting,etc.