Leader LBO-516 Instruction Manual - page 14
If a low-resistance ground connection between oscilloscope
and circuit is not established, enormous amounts of hum will
appear in the displayed signal. Generally, the outer conductor
of shielded cable provides the ground connection. If you are
using plain lead wire, be certain to first connect a ground
wire between the LBO-516 Ground connector (12) and the
chassis or ground bus of the circuit under observation.
WARNING: The LBO-516 has an earth-grounded
chassis (via the 3-prong power cord). Be certain the
device to which you connect the scope is transformer
operated. Do NOT connect the LBO-516 or any other
test equipment to "AC/ DC", "hot chassis", or
"transformerless" devices. Similarly, do NOT connect
the LBO-516 directly to the AC power line or any
circuitry connected directly to the power line. Damage
to the instrument and severe injury to the operator may
result from failure to heed this warning.
2-3-2 Single-trace Operation
Single trace operation with single timebase and internal
triggering is the most elementary operating mode of the
LBO-516. Use this mode when you want to observe only a
single signal, and not be disturbed by other traces on the
CRT. Since the LBO-516 is fundamentally a two-channel in-
strument, you have a choice for your single channel. Channel
1 has an output terminal; use channel 1 if you also want to
measure frequency with a counter while observing the
waveform. Channel 2 has a polarity-inverting switch. While
this adds flexibility, it is not ordinarily used in single-trace
operation.
The LBO-516 is set up for single-trace operation as fol-
lows:
1. Set the following controls as indicated. Any controls not
mentioned here or in the following steps can be
neglected. Note that the trigger source selected (CH-1 or
CH-2 SOURCE) must match the single channel selected
(CH-1 or CH-2 V MODE).
VARIABLE VOLTS/DIV Fully CW,
controls (11) and pushed in
AC/GND/DC switches (16) .......... AC
V MODE switches (21) ............... CH- 1 or CH-2*
CH-2 INV switch (19) .................. Out
A INTEN control (3) ................... APS**
FOCUS control (5) ..................... APS**
POWER switch (1) ..................... In
HORIZ DISPLAY switches (31) ..... A
B TIME/DIV switch (25) .............. 0.5/KS
A VARIABLE control (26) ............ Fully CW, and
pushed in
SOURCE switch (34) .................. CH- 1 or CH-2*
COUPLING switch (36) ............... AC
SWEEP MODE switches (37) ........ AUTO
HOLDOFF control (42) ................ Pulled out
PRESET level
Horizontal POSITION control (29) ..APS**
*These selections must match.
**As previously set.
2. Use the corresponding vertical POSITION control (17)
or (18) to set the trace near mid screen.
3. Connect the signal to be observed to the corresponding
input connector (14) or (15), and adjust the
corresponding VOLTS/DIV switch (10) so the
displayed signal is totally on screen.
CAUTION: Do not apply a signal
greater than 400 V (DC + AC peak).
4. Set the A TIME/DIV switch (24) so the desired number
of cycles of signal are displayed. For some
measurements just 2 or 3 cycles are best; for other
measurements 50-100 cycles (appears like a solid band)
works best.
5. If the signal you wish to observe is so weak that even
the 5 mV position of the VOLTS/DIV switch cannot
produce sufficient trace height for triggering or a usable
display, pull the VARIABLE (X10 MAG) control (11)
outwards. This produces 1 mV/div sensitivity when the
VOLTS/DIV switch is set to 10 mV, and .5 mW/div
when it is set to 5 mV.
6. If the signal you wish to observe is so high in frequency
that even the .02/KS position of the A TIME/DIV switch
results in too many cycles displayed, pull the A VARI-
ABLE (X10 MAG) control (28) outwards. This
increases the effective sweep speed by a factor of 10, so
.02 KS/div becomes 2KS/div, .1/KS becomes .01 KS/div,
etc. The 2KS/div sweep speed achievable by
magnification is fast enough to display a single cycle of
a 50 MHz signal across the CRT face!
7. If the signal you wish to observe is either DC or low
enough in frequency that AC coupling attenuates or
distorts the signal, flip the AC/GND/DC switch (16) to
DC.
CAUTION: If the observed waveform is low-level
AC, make certain it is not riding on a high-
amplitude DC voltage.
2-3-3 Triggering Alternatives
Triggering is often the most difficult operation to
perform on an oscilloscope because of the many options
available and the exacting requirements of certain signals. By
using PRESET trigger level and the AUTO sweep mode,
error-free triggering is obtainable from the LBO-516. These
were the trigger options selected for the single-trace
operating procedure described in paragraph 2-3-2, and the
multi-trace and dual-time base operating modes described in
the following section. They will in fact work well with most
signals. However, for complex or otherwise difficult signals,
the LBO-516 operator may choose from an extensive
selection of trigger options. These are categorized as trigger-
source options, coupling options, sweep mode, and
triggerpoint selection.
Sweep Mode Selection. Normally, the CRT beam is not
swept horizontally across the face of the CRT until a sample
of the signal being observed, or another signal harmonically
related to it, triggers the timebase. This is the situation when
NORM SWEEP MODE (37) is selected. However, this trig-
ger mode is inconvenient because no baseline appears on the
CRT screen in the absence of an input signal, or if the trigger
controls are improperly set. Since an absence of a trace can
also be due to an improperly set vertical position control or
VOLTS/DIV switch, much time can be wasted determining
the cause. The AUTO sweep mode solves this problem by
causing the timebase to automatically free run when not
triggered. This yields a single horizontal line with no signal,
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