Tektronix 502A, Instruction Manual

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Calibration Procedure — Type 502A
13. Coaxial "Straight" Connector. (1)
14. Jumpers, 6 inch with banana plugs. (3)
15. A constant amplitude sine-wave generator having output
frequencies of 1 kilocycle, 50 kilocycles, 100 kilocycles, 200
kilocycles, 400 kilocycles and 1 megacycle. The generator
should also have a variable output amplitude from 500
μvolts to 2 volts.
If a constant amplitude generator is not available to
cover the above ranges, any generator which has the
proper frequencies and output amplitudes may be used.
When using a generator which does not have a constant
amplitude feature the test oscilloscope should be used
to monitor the output of the generator. By use of the
oscilloscope the output signal from the generator may be
kept at a constant amplitude.
By the use of a DB box or an attenuator system, the
signal going from the sine-wave generator to the Type 502A
may be reduced to the proper amplitude for the high sensi­
tivity ranges, while at the same time the signal going from
the sine-wave generator to the test oscilloscope may be kept
at a high amplitude to enable monitoring for a constant am­
plitude of signal out of the sine-wave generator.
Preliminary
NOMINAL RESISTANCES OF
POWER SUPPLIES
SUPPLY APPROX. RESISTANCE TO
GROUND
-150V 3.5 k
100 V 4 k
350V 10k
Connect the power cord and the ac voltmeter to the out­
put of the autotransformer. Rotate the POWER AND SCALE
ILLUM control clockwise to the ON position and adjust the
autotransformer for an output of 117 volts (or 234 volts).
Allow the instrument to warm up for several minutes before
proceeding with the calibration adjustments. During cali­
bration, periodically check the input voltage to the instru­
ment and adjust the autotransformer as necessary to main­
tain the voltage at 117 or 234 volts 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.
Preset the front-panel controls of the Type 502A
as follows:
POWER AND SCALE ILLUM PWR OFF
INTENSITY full counterclockwise
INTENSITY BALANCE midrange
FOCUS (both beams) midrange
TRIGGERING LEVEL midrange
TRIGGER SELECTOR + LOWER AC
MODE Switch NORMAL
TIME/CM 1 mSEC
VARIABLE CALIBRATED
HORIZONTAL DISPLAY 2 EXT VOLTS/CM
HORIZONTAL POSITION midrange
AMPLITUDE CALIBRATOR OFF
HORIZ DEF PLATE TIME BASE AMP
SELECTOR
The following applies to both vertical amplifiers:
Input Selector A-DC
SENSITIVITY .2 VOLTS PER CM
VARIABLE CALIBRATED
DC BAL. control will be set later.
VERTICAL POSITION
midrange
Before applying power to the instrument the resistances
of the power supplies should be checked. The typical resis­
tances of the supplies may be found in the chart below.
1. Low-Volfage Power Supply
Connect the dc voltmeter to the output of the —150 volt
power supply. Power supply output test points are shown in
Fig. 5-2. Set the —150 Control for a reading of —150 volts.
Check that the outputs of the —6.2, +100 and +350 volt
supplies are within the spe or — 3% tolerances.
If either the +100 or +350 volt supplies are out of tolerance,
reset the —150 control slightly until all power supply
voltages are within tolerances.
Vary the output of the autotransformer between 105 and
125 volts (or between 210 and 250 volts) to check the regula­
tion of
the low voltage power supplies. The power supplies
must regulate within + or — 3% of their correct voltages.
Fig. 5-2. Power Supply voltage test points.
5-2
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