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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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.