Tektronix 543B, Instruction Manual

Page: 28 / 90

Calibration — Type 543B/RM543B
Other Controls
HORIZONTAL POSITION
VERNIER (HORIZONTAL
POSITION)
EXTERNAL HORIZONTAL
VOLTS/CM
VARIABLE (EXTERNAL
HORIZONTAL VOLTS/
CM)
AMPLITUDE CALIBRATOR
Midrange
Midrange
10
CALIBRATED
OFF
Before installing the Type TU-7 and applying power to
the instrument the resistances of the power supplies should
be checked. The typical resistances of the supplies may
be found in the chart below.
Nominal Resistances
of Power Supplies
Supply
Approx. Resistance to
Ground
-150 2k
+ 100 2k
+225 2k
+350 1 k
+500 15k
Fig. 5-1. Low-voltage power supply fest point locations.
Install the Type TU-7 and preset its controls as follows:
Vertical Position Centered
Test Function Low Load
Other Controls As is
Connect the power cord and the ac voltmeter to the out­
put of the autotransformer. Turn the power switch to the
ON position and adjust the autotransformer for an output
voltage to match the design center voltage of the oscillo­
scope. Allow the instrument to warm up for several minutes
before proceeding with the calibration adjustments. During
calibration, periodically check the input voltage to the
instrument and adjust the autotransformer as necessary to
maintain the voltage at the design center voltage except
when the power supply regulation is being checked.
CAUTION
Do not reset the —150 control unless the power
supply voltages are actually out of tolerance or
you are planning to perform a complete calibra­
tion of the instrument.
Check the delay time delay relay. The relay armature
should pull in with a "click" sound after 15 to 60 seconds
has elapsed.
PROCEDURE
1. Low-Voltage Power Supplies
Measure the output voltage of the —150v, +100 v,
+
225 v, +350 v, and +500 v regulated supplies at the
points indicated, in Fig. 5-1. The output voltage of the
—150-volt and the other regulated supplies must be within
3% of their rated values. Set the —150 control (see Fig.
5- 2) so that all of these voltages are within the specified
tolerance.
To check the regulation of the power supplies, set the
Test Function switch of the Type TU-7 to High Load and
adjust the line voltage for a voltage 10% lower than your
design center voltage. Now check the voltage of each
supply. The —150v, +100v, +225 v and +350 v supplies
should still be within 3% of their proper values. The 4-500 v
supply should still be within 5% of its proper value.
The power supply ripple is checked by connecting a one
times probe from the test oscilloscope to the supply being
checked. The table below gives the approximate ripple
amplitudes of each power supply.
After the power supplies have been checked on low line
voltage, the line voltage should be raised 10% above
design center voltage and the Test Function switch of the
Type TU-7 set to Low Load. Repeat the voltage and ripple
checks. The same limits apply.
When the power supply regulation checks are completed
return the line voltage to the design center voltage.
Typical Ripple Amplitudes
Supply
Typical Ripple
-150
5 mv
+ 100
10 mv
+ 225
5 mv
+350 20
mv
+ 500
20 mv
2. AMPLITUDE CALIBRATOR Adjustments
CAL ADJ R879 should be set to provide exactly 4-100
volts at the CAL TEST PT when the AMPLITUDE CALIBRATOR
switch is in rhe OFF position. Under these conditions, the
CAL OUT voltages should be within 3% of the front-panel
readings.
5-2