+
BK PRECISION
®
INSTRUCTION
MODELS 2120B
MANUAL
and 2125A
30 MHz DUAL-TRACE OSCILLOSCOPES
+
®
BK PRECISION
TEST INSTRUMENT SAFETY
WARNING
Normal use of test equipment exposes you to a certain amount of danger from electrical shock because
testing must often be performed where exposed high voltage is present. An electrical shock causing
10milliampsofcurrentto pass throughtheheart will stop most human heartbeats. Voltageas low as35 volts
dc or ac rms should be considered dangerous and hazardous since it can produce a lethal current under
certain conditions. Higher voltage poses an even greater threat because such voltage can more easily
produce a lethal current. Your normal work habits should include all accepted practices that will prevent
contact with exposed high voltage, and that will steer current away from your heart in case of accidental
contact with a high voltage. You will significantly reduce the risk factor if you know and observe the
following safety precautions:
1. Don’t expose high voltage needlessly in the equipment under test. Remove housings and covers only when necessary.
Turn off equipment while making test connections in high-voltage circuits. Discharge high-voltage capacitors after
removing power.
2. If possible, familiarize yourself with the equipment being tested and the location of its high voltage points. However,
remember that high voltage may appear at unexpected points in defective equipment.
3. Use an insulated floor material or a large, insulated floor mat to stand on, and an insulated work surface on which to
place equipment; make certain such surfaces are not damp or wet.
4. Use the time-proven “one hand in the pocket” technique while handling an instrument probe. Be particularly careful to
avoid contacting a nearby metal object that could provide a good ground return path.
5. When using a probe, touch only the insulated portion. Never touch the exposed tip portion.
6. When testing ac powered equipment, remember that ac line voltage is usually present on some power input circuits such
as the on-off switch, fuses, power transformer, etc. any time the equipment is connected to an ac outlet, even if the
equipment is turned off.
7. Some equipment with a two-wire ac power cord, including some with polarized power plugs, is the “hot chassis” type.
This includes most recent television receivers and audio equipment. A plastic or wooden cabinet insulates the chassis
toprotect the customer. When the cabinet is removed for servicing, a serious shock hazard exists if the chassis is touched.
Not only does this present a dangerous shock hazard, but damage to test instruments or the equipment under test may
result from connecting the ground lead ofmost test instruments (includingthis oscilloscope) to a “hot chassis”. To make
measurements in “hot chassis” equipment, always connect an isolation transformer between the ac outlet and the
equipment under test. The B+K Precision Model TR-110 or 1604A Isolation Transformer, or Model 1653A or 1655A
AC Power Supply is suitable for most applications. To be on the safe side, treat all two wire ac powered equipment as
“hot chassis” unless you are sure it has an isolated chassis or an earth ground chassis.
8. Never work alone. Someone should be nearby to render aid if necessary. Training in CPR (cardio-pulmonary
resuscitation) first aid is highly recommended.
Instruction Manual
for
+
BK PRECISION
®
Models 2120B
and 2125A
30 MHz
Dual-Trace Oscilloscopes
©2000 B+K Precision Corp.
This symbol on oscilloscope means “refer to instruction manual
for further precautionary information”. This symbol appears in the
manual where the corresponding information is given.
®
+
1031 Segovia Circle, Placentia, CA 92870
TABLE OF CONTENTS
Page Page
TEST INSTRUMENT SAFETY . . . . . . inside front cover
FEATURES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
SPECIFICATIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
CONTROLS AND INDICATORS . . . . . . . . . . . . . . . . . . 7
General Function Controls . . . . . . . . . . . . . . . . . . . . . . 7
Vertical Controls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Horizontal Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Triggering Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Rear Panel Controls . . . . . . . . . . . . . . . . . . . . . . . . . . 10
OPERATING INSTRUCTIONS. . . . . . . . . . . . . . . . . . . 11
Safety Precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Equipment Protection Precautions. . . . . . . . . . . . . . . 11
Operating Tips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Initial Starting Procedure . . . . . . . . . . . . . . . . . . . . . . 12
Single TraceDisplay . . . . . . . . . . . . . . . . . . . . . . . . . 12
Dual Trace Display. . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Triggering. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Magnified Sweep Operation . . . . . . . . . . . . . . . . . . . 15
OPERATING INSTRUCTIONS (Continued)
X−Y Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Video Signal Observation . . . . . . . . . . . . . . . . . . . . . 15
Application Guidebook. . . . . . . . . . . . . . . . . . . . . . . 15
Delayed Sweep Operation. . . . . . . . . . . . . . . . . . . . . 15
Component Test Operation . . . . . . . . . . . . . . . . . . . . 16
MAINTENANCE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Fuse Replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Line Voltage Selection. . . . . . . . . . . . . . . . . . . . . . . . 20
PeriodicAdjustments. . . . . . . . . . . . . . . . . . . . . . . . . 20
Calibration Check . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Instrument Repair Service. . . . . . . . . . . . . . . . . . . . . 21
APPENDIX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Important Considerations for Rise Time and
Fall Time Measurements . . . . . . . . . . . . . . . . . . . . 22
Service Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Limited Warranty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
“Guidebook To Oscilloscopes”
Availability . . . . . . . . . . . . . . . . . . . . . inside back cover
2
FEATURES
LOW COST,HIGH PERFORMANCE
B+K Precision’sentry leveloscilloscopes, Models 2120B
and 2125A, are economically priced to equal the competition, but offer higher performance than the competition.For
example, most competitor’sentry level oscilloscopes have a
20 MHz bandwidth, while B+K Precision’s Models 2120B
and 2125A offer a 30 MHz bandwidth. These oscilloscopes
are built by and backed by B+K Precision, a company that
has been selling reliable, durable, value priced test instruments for over 50 years.
CRT FEATURES
Rectangular CRT
Rectangular CRTwith large 8 x 10 centimeterviewing
area. On Model 2125A, graticule is equipped with
variable scale illumination.
Convenience
Tracerotation electrically adjustable from front panel.
0%, 10%, 90%, and 100% markersfor rise time measurements.
DUAL TRACEFEATURES
Dual Trace
Models2120Band2125Aeachhavetwovertical input
channels for displaying two waveforms simultaneously. Selectable single trace (either CH 1 or CH 2) or
dual trace. Alternate or chop sweep selectable at all
sweep rates.
Sum and Difference Capability
Permits algebraic addition or subtraction of channel 1
and channel 2 waveforms, displayedas a single trace.
Useful for differentialvoltageand distortion measurements.
HIGH FREQUENCY FEATURES
Wide Bandwidth
Conservatively-rated −3 dB bandwidth is dc to 30
MHz.
Fast Rise Time
Rise time is less than 12 ns.
Fast Sweep
Maximum sweep speed of 10 ns/div(with X10 MAG)
assures high frequencies and short-duration pulses are
displayed with high resolution.
VERTICAL FEATURES
High Sensitivity
5 mV/div sensitivityfor full bandwidth. High-sensitivity 1 mV/div and 2 mV/div using PULL X5 gain
control.
Calibrated VoltageMeasurements
Accurate voltage measurements (±3%) on 10 calibrated ranges from 5 mV/div to 5 V/ div. Vertical gain
fully adjustable between calibrated ranges.
SWEEP FEATURES
Calibrated Time Measurements
Accurate (±3%) time measurements. The main sweep
has 23 calibrated ranges from 2 S/div to 0.1 µS/div.
The delayed sweep on the Model 2125A has 23 calibrated ranges from 2 S/div to 0.1 µS/div. Sweep time
is fully adjustable between calibrated ranges.
X10 Sweep Magnification
Allows closer examination of waveforms, increases
maximum sweep rate to 10 nS/div.
DUAL TIME BASE FEATURES (Model 2125A)
Dual Sweep Generators
Main sweep gives normal waveform display, delayed
sweepmaybe operated atfastersweep speedtoexpand
a portion of the waveform.
Four Sweep Modes
Choice of main sweep only, delayed sweep only,
main sweep and delayed sweep sharing the trace
(percentage of main /del aye d swee p adjustable), or
X−Y.
Adjustable Start Of Delayed Sweep
DELAYTIME POSition control allows adjustment of
delayed sweep starting point.
TRIGGERING FEATURES
Two TriggerModes
Selectable normal (triggered) or automatic sweep
modes.
Triggered Sweep
Sweep remains at restunless adequate trigger signal is
applied. Fully adjustable trigger level and (+) or (−)
slope.
3
FEATURES
AUTO Sweep
Selectable AUTO sweep provides sweep without trigger input, automatically reverts to triggered sweep
operation when adequate trigger is applied.
Five TriggerSources
Five trigger source selections, including CH 1, CH 2,
alternate, EXT, and LINE.
Video Sync
Frame(TV V) or Line (TV H) triggering selectablefor
observingcomposite video waveforms.TV-Hposition
can also be used as low frequency reject and TV-V
position can be used as high frequency reject.
Variable Holdoff
Trigger inhibit period after end of sweep adjustable.
Permits stable observation of complex pulse trains.
OTHER FEATURES
X−Y Operation
Channel 1 can be applied as horizontal deflection
(X-axis) while channel 2 provides vertical deflection
(Y-axis).
Built-in Probe Adjust Square Wave
A 2 V p-p, 1 kHz square wave generator permits probe
compensation adjustment.
Component TestFunction (Model 2125A)
Built-inX−Ytypecomponenttesterapplies fixedlevel
ac signal to components for display of signature on
CRT.
Channel 2 (Y) Output (Model 2125A)
A buffered 50Ω output of the channel 2 signal is
available at the rear panel for driving a frequency
counter or other instruments. The output is 50 mV/div
(nominal) into 50Ω.
Z-Axis Input (Model 2125A)
Rear panel Z-Axis input allows intensity modulation.
Supplied With Two Probes
4
SPECIFICATIONS
CRT:
Type: 6-inch rectangular with integral graticule,
P31 phosphor.
DisplayArea:8 x 10 div (1 div = 1 cm).
AcceleratingVoltage:2kV.
Phosphor:P31.
Trace Rotation: Electrical, front panel adjustable.
Scale Illumination: Continuously variable (Model 2125A).
Beam Finder (Model 2125A).
VERTICAL AMPLIFIERS (CH 1 and CH 2)
Sensitivity: 5 mV/div to 5 V/div, 1 mv/divto 1 V/divat
X5 MAG.
Attenuator:10 calibrated steps in 1-2-5 sequence. Vernier
control provides fully adjustable sensitivity between
steps; range 1/1 to at least 1/3.
Accuracy:±3%, 5 mV to 5 V/div;5%, at X5 MAG.
Input Resistance:1MΩ±2%.
Input Capacitance: 25 pF ±10 pF.
Frequency Response:
5 mV/div to 5 V/div:
DC to 30 MHz (−3 dB).
X5 MAG:
DC to 10 MHz (−3 dB).
Rise Time:
12 nS; 35 nS at X5 MAG.
Overshoot:Less than 5%.
Operating Modes:
CH 1: CH 1, single trace.
CH 2: CH 2, single trace.
DUAL: CH 1 and CH 2, dual trace.
Alternate or Chop selectable at
any sweep rate.
ADD: Algebraic sum of CH 1 + CH 2.
Chop Frequency:Approximately 500 kHz.
PolarityReversal:CH 2 invert.
MaximumInput Voltage:400 V (dc + ac peak).
HORIZONTAL AMPLIFIER
(Input through channel 1 input)
X−Y mode:
CH 1 = X axis.
CH 2 = Y axis.
Sensitivity: Same as vertical channel 2.
Input Impedance: Same as vertical channel 2.
Frequency Response:
DC to 1 MHz (−3 dB).
X-Y Phase Difference: 3° or less at 50 kHz.
MaximumInputVoltage: Same as verticalchannel 1.
SWEEP SYSTEM
Operating Modes:
Model 2125A: Main, Mix (both main and delayed
sweep displayed), Delay (only delayed sweep
displayed), X−Y.
Model 2120B: Main only.
Main Time Base: 0.1 µS/div to 2.0 S/div in 1-2-5
sequence,23 steps. Vernier control provides fully
adjustablesweep time betweensteps.
DelayedTime Base (Model 2125A only): 0.1 µS/div to
2.0 S/div in 1-2-5 sequence, 23 steps.
Accuracy:±3%, except ±6% on 0.2 S/div and ±20% on
0.1 µS/div.
Sweep Magnification: X10 ±10%.
Holdoff: Continuously adjustable for main time base from
NORM to 5 times normal.
Delay Time Position: Control sets percentageof display
that is devoted to main and delayed sweep.
Delay Jitter: 1/10,000 of full scale sweep time.
TRIGGERING
Trigger Modes:
AUTO (free run), NORM, TV-V, TV-H.
Trigger Source:
CH 1, CH 2, Alternate, EXT, LINE.
Slope:
(+) or (–).
5
SPECIFICATIONS
Trigger Coupling:
AUTO: Sweep free-runs in absence of
suitable trigger signal.
NORM: Sweep triggered only by adequate
trigger signal.
TV-V: Video vertical sync pulses are
selected. Also usable for high
frequency reject.
TV-H: Video horizontal sync pulses are
selected. Also usable for low
frequency reject.
Trigger Sensitivity:
Auto: 1.5 div (internal)
≥0.5 Vp-p (external)
100 Hz – 40 MHz (2125A)
100 Hz – 30 MHz (2120B)
Norm: 1.5 div (internal)
≥0.5 Vp-p (external)
100 Hz – 40 MHz (2125A)
DC – 30 MHz (2120B)
TV-V: 1.0 div (internal)
≥0.5 Vp-p (external)
DC – 1 kHz (2125A)
20 Hz – 1 kHz (2120B)
TV-H: 1.0 div (internal)
≥0.5 Vp-p (external)
1 kHz– 100 kHz
MaximumExternalTriggerVoltage: 300 V (dc + ac
peak).
COMPONENTTESTER (Model 2125A)
ComponentsTested: Resistors, capacitors, inductors, and
semiconductors.
TestVoltage: 6 V rms maximum(open).
TestCurrent:11 mA maximum (shorted).
TestFrequency:Line frequency (60 Hz in USA).
OTHER SPECIFICATIONS
Cal/ProbeCompensation Voltage:2 V p-p ±3% square
wave,1 kHz nominal.
CH 2 (Y) Output (Model 2125A):
Output Voltage: 50 mV/div (nominal into 50 ohm
load).
Output Impedance: Approximately 50 ohms.
Frequency Response:20 Hz to 30 MHz, −3 dB.
IntensityModulation (Model 2125A)
Input Signal: TTL level,intensity increasing with
more positive levels, decreased intensity with more
negative levels.
Input Impedance: Approximately 50 kΩ.
Usable Frequency Range: DC to 5 MHz.
Maximum Input Voltage: 30 V (dc + ac peak).
Power Requirements: 100–130 VAC or 200–260 VAC,
50/60 Hz, 38 watts.
Dimensions (H 3 W 3 D):
5.2″ 3 12.8″3 15.7″
(132 3 324 3 398 mm).
Weight: 16.8 lbs (7.6 kg).
Environment:
Within Specified Accuracy: +10° to +35° C, 10–80%
relative humidity.
Full Operation: 0° to +50° C, 10–80% relative
humidity.
Storage: −30° to +70° C, 10–90% relative humidity.
ACCESORIES SUPPLIED:
Two Switchable X1/X10 Probes.
Instruction Manual.
AC Line Cord.
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