Tektronix 502A

Calibration Procedure — Type 502A
Using the test oscilloscope, check the ripple voltage at
the output of each power supply when the autotransformer
is adjusted for 117 volts. Swing the autotransformer output
voltage from 105 volts to 125 volts while observing the
amount of ripple on the test scope. The power supply ripple
should remain about the same amplitude from low line to
high line voltage. Return the line voltage to 117 volts.
TYPICAL RIPPLE AMPLITUDES
Supply
Typical Ripple
-6.2V
8mv at 105 and 1 15V
-150V
8mv + 50% at 105 and 125V
+ 100V
8mv + 50% at 105 and 125V
+350V 25mv + 50% at 105 and 125V
2. R879, CAL AMPL
Connect the d c voltmeter to the junction of R885 and
the cathode of V873B. See Fig. 5-3. Adjust R879, for a
reading of +50 volts on the d c voltmeter. Turn the AMPLI 
TUDE CALIBRATOR switch to 5 m V and check for a read 
ing of 22.5 to 27.5 volts on the d c voltmeter.
Fig. 5-3. Location of the Amplitude Calibrator test point.
3. CRT Alignment
Turn the TRIGGERING LEVEL to RECURRENT, HORIZON 
TAL DISPLAY switch to NORMAL and turn up the INTENS 
ITY Control until a trace is visible (it may be necessary to
adjust the Vertical Positioning control). Adjust FOCUS and
ASTIGMATISM for sharpest trace (narrowest trace width).
Position one of the traces under a horizontal division of the
graticule near the vertical center of the crt. Loosen the
clamp at the base of the crt and push the crt against the
graticule, then tighten the clamp. Now with the red knob,
near the bottom of the clamp, rotate the crt until the trace
runs parallel to the horizontal lines of the graticule.
4. HV
Remove the right side H V shield and with a d c voltmeter
connected to the center arm of R833 (HORIZ SENS BAL).
Adjust R833 until a reading of +100 volts is obtained from
the center arm to ground.
Now connect the voltmeter from the H V TEST POINT to
ground. Adjust the HV Control for a reading of — 2900
volts. Replace HV shield.
To check HV regulation place the HORIZONTAL
DISPLAY switch to 2 EXT VOLTS/CM. Position the focused
spots onto the screen. Now while observing the focused
spot, decrease the line voltage with the autotransformer to
105 volts. The spots should not have shown any blooming
as the line voltage was decreased. Return the line voltage
to 117 volts and the HORIZONTAL DISPLAY switch to the
NORMAL position.
5. INTENSITY BALANCE Control
Increase the INTENSITY Control to the point where the
traces have a halo forming around them. While observing
the halo around each trace adjust the INTENSITY BALANCE
Control until the brightness of the halos is the same.
Turn the INTENSITY down to the normal level and observe
the two traces. The intensities should still be about the same.
6. ASTIG UPPER, ASTIG LOWER
Adjustment
Place the HORIZONTAL DISPLAY switch in the 2 EXT
VOLTS/CM position and rotate both the UPPER and LOWER
BEAM FOCUS Controls fully clockwise. Position both beams
onto the screen, and adjust the ASTIG UPPER and ASTIG
LOWER Controls so that both defocused spots are as nearly
circular as possible. Adjust the UPPER BEAM and LOWER
BEAM FOCUS Controls so that both spots are in sharp
focus. Return the HORIZONTAL DISPLAY switch to NORMAL.
NOTE
If a line appears instead of a spot, the high-
voltage shields are not in place.
CAUTION
It is quite easy to damage the crt phosphor when
the spots are in sharp focus. The INTENSITY
Control should also be kept as low as possible
when doing the above adjustment.
7. GEOM
Connect 1 MILLISECONDS time marker from a Type 180A
to both A inputs. Position the two traces so that only the
®I
5-3