Preliminary Procedure; Calibration Procedure - Tektronix 3A74 Instruction Manual

Calibration — Type 3A74
PRELIMINARY PROCEDURE
a. Remove the left-side panel from the oscilloscpe.
NOTE
As you go through the procedure, various inter-
connecting plug and/or socket pins are called out
as test points. Since different types of 560-Series
oscilloscopes can be used with the Type 3A74
being calibrated, test-point accessibility differs
from oscilloscope to oscilloscope due to their phys-
ical layout. Therefore, remove any additional
panels, as required, during the procedure.
b. Connect a 30" flexible cable plug-in extension {item 5)
to the Type 3A74 interconnecting plug and to the oscil-
loscope interconnecting socket located in the vertical
opening (Y-axis) of the oscilloscope.
c. Install a (real-time) time-base unit {item 2) in the oscillo-
scope for horizontal deflection of the beam, if the as-
sociated oscilloscope requires a time-base unit.
d, Connect the power cord of the oscilloscope to the proper
operating voltage for which the oscilloscope is wired.
e, Turn on the oscilloscope and allow about 15 minutes for
warm-up and complete stabilization,
f, Preset the Type 3A74 front-panel controls {all channels)
b. Meter reading should be +-50 volts, within a tolerance
of 5 volts.
c. Disconnect the voltmeter.
CAUTION
When connecting to test points in the Type 3A74
or to the interconnecting plug and socket pins, be
sure to use test prods or probe tips that are com-
pletely insulated, except for the very tip, to avoid
accidental shorts to adjacent leads or connections.
2. Adjust DC BAL. (All Channels)
a. Set channel 1 MODE switch to NORM.
b, Adjust the oscilloscope Intensity contro! for desirable
trace brightness.
c, Adjust channel 1 DC BAL. control for minimum vertical
trace shift as the channel 1 VAR. GAIN control is
rotated several times from the CAL. detent position
clockwise to minimum gain and back again.
d. After adjusting the DC BAL, control, set the VAR, GAIN
control to the CAL, position,
e. Set channel! 2 MODE switch to NORM, and repeat steps
2a, 2c and 2d using the appropriate channel 2 con-
trols.
f. After adjusting channel 2 DC BAL. control, proceed in
the same manner (using steps 2a, 2c, and 2d as a guide)
to adjust the DC BAL. controls for channels 3 and 4.
NOTE
If the DC BAL. control for a channel does not
have sufficient range, there may be excessive dc
imbalance between tubs V423 and V433 in that
channl. Replace the tube causing the greatest im-
balance, allow about 15 minutes warm-up time,
and repeat step 2,
as follows:
AC-GND-DC bc
VOLTS/DIV. 02
VAR. GAIN CAL.
POSITION Midrange
MODE OFF
CHOP.-ALT. ALT.
TRIGGER Pushed in
g. Preset the Type 2B67 Time-Base Unit or equivalent as fol-
lows:
Time/ Div. 1 mSEC
Variable Time/Div. Calibrated
Mode Norm.
Triggering Level Free Run*
Triggering Slope +
Triggering Coupling AC Slow**
Triggering Source Int.
Position Centered
5X Mag. Off
"Use Auto. or Line Triggering if your time-base does not have
co Free Run switch position to obtain @ trace on the ert.
**"Use AC if your time base does not
position.
have an AC Slow switch
CALIBRATION PROCEDURE
1. Check Zener Regulated Voltage
a. Connect a de voltmeter between the D494/R494 junction
(see Fig. 6-1) and ground.
6-2
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0494/R494 0463
Junction Emitter
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Fig. 6-1. Right side view, rear portion of the Type 3A74, showing
the location of the test points.
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