Tektronix 2445, Instruction Manual

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Operating Inform ation—2445 Service
VERTICAL
Refer to Figure 2-3 for location o f items 10 through 17.
@
CH 1 OR X and CH 2 Input Connectors—Provide
fo r application of external signals to the inputs of
Channel 1 and Channel 2 vertical attenuators. A
signal applied to the CH 1 OR X connector provides
the horizontal deflection fo r an X-Y display. Any
one or all of the channels (including Channel 1)
may supply the signal fo r the X-Y display vertical
deflection. These connectors each include a coding­
ring contact that activates the scale-factor-switching
circuitry whenever a scale-factor-switching probe
is connected. The internal circuitry recognizes
Tektronix attenuation-coded probes.
Input Coupling Switches and Indicators—Select the
method of coupling input signals to the Channel 1
and Channel 2 vertical attenuators and indicate the
selection made. If the Channel 1 and Channel 2 input
signals are both AC coupled and if both input cou­
pling switches are pushed up together, the instrument
automatically performs a dc balance o f Channel 1
and Channel 2 vertical circuitry.
1 M12 AC—Input signal is capacitively coupled to
the vertical attenuator. The dc component o f the
input signal is blocked. The low-frequency lim it
(—3 dB point) is 10 Hz or less when using either
a IX probe or a coaxial cable and is 1 Hz or less
when using a properly compensated 10X probe.
1 M12 GND—The input of the vertical amplifier
is grounded to provide a zero (ground) reference-
voltage display. Input resistance is 1 M12 to ground.
This position of the switch allows precharging of
the input-coupling capacitor to prevent a sudden
shift o f the trace if AC input coupling is selected
later.
1 M12 DC—All frequency components of the input
signal are coupled to the vertical attenuator. Input
resistance is 1 M12 to ground.
1 M12 GND—In this position, the switch operates
exactly the same as previously described.
50 12 DC—A ll frequency components of the input
signal are coupled to the vertical attenuator, with
the input terminated by 50 12 to ground. If exces­
sive signal is applied to either the CH 1 or the
CH 2 input connector while 50 12 DC input
coupling is selected, input coupling w ill revert to
1 M12 GND and a crt readout w ill indicate the
overloaded condition. Moving the input coupling
switch o f the affected channel removes the over­
load message. While power is o ff, coupling is at
1 M12GND.
^ 2 ) Channel 1 and Channel 2 V O LTS/D IV Switches—
Select vertical deflection factor settings in a 1-2-5
sequence w ith 11 positions. The VAR control must
be in the detent (fully clockwise) position to obtain
a calibrated deflection factor. Basic deflection factors
are from 2 mV per division to 5 V per division.
Deflection factors shown in the crt readout reflect
actual deflection factors in use when Tektronix
attenuation-coded probes are connected to the
inputs.
(?3) VAR Controls—Provide continuously variable, un­
calibrated deflection factors between the calibrated
settings of the VO LTS/DIV switches. These controls
vary the deflection factors from calibrated (fully
clockwise detent position) to at least 2.5 times the
calibrated deflection factor (fully counterclockwise
position). When out o f the calibrated detent, a greater
than ( > ) sign appears in fro n t of the associated
VO LTS/DIV readout display.
Figure 2-3. Vertical controls and CH 1 OR X and CH 2 connectors.
2-5