Sect. IV Page 12 Model 122A
3) Measure power supply output voltages with line spot. Set pointer on INTENSITY knob to 9 o?clock
voltage set to 115 v. The points at which the and adjust Intensity Limit control, R322, so that
various voltages appear can be identified by the the CRT spot is just extinguished. These adjust-
wire color code given in Table 4-5. The voltages ments are usually required only if the setting of
will normally be within the limits given. Poten- the high voltage control, R308, has been changed.
tiometer Low Voltage Set, R344, can be adjusted,
if necessary, to set the -150 volt supply within
the limits in Table 4-5. If the voltages are within
limits and pass steps 4 and 5 that follow, do not 4-10 TRIGGER GENERATOR
adjust in an attempt to refine the existing control
settings. The Trigger Generator must be working to adjust
the Vertical and Horizontal Amplifiers. Also,
If adjustment of the -150 volt supply is necessary, these amplifiers must be adjusted before the Saw-
check all Sweep Generator and Calibrator adjust- tooth Generator can be adjusted. Check the Trigger
ments. Generator as follows:
1) Check power supply according to paragraph 4-9.
TABLE 4-5. REGULATED POWER SUPPLY
2) Adjust Stability Control, R228.
NOMINAL NORMAL COLOR VOLTAGE Set A VERT SENSITIVITY to OFF
VOLTAGE -7- RIPPLE CODE TOLERANCE* B VERT SENSITIVITY to OFF
SWEEP TIME to .5 MILLISECONDS/CM
-150 3 mv Violet * 2 volts SYNC to INT
TRIGGER LEVEL fully counterclockwise but
+ 380 40 Red *lo not in AUTO.
VERT PRESENTATION to A or B
+ 100 4 Yellow *3
Connect an @410B (-100 v dc range) to pin 8 of
+ 24 40 White** * 1 V203. Slowly rotate Stability Control, R228,
counterclockwise until the sweep starts free-run-
With line voltage set to 115 v. ning. Then back control off until it just stops.
Take a voltage reading which should be about
c* In vertical amplifiers. -78 volts. Set R228 to 2.0 volts more positive than
the last reading. This is the proper setting for
the stability control.
4) You may wish to check regulation of each power 3) External Trigger Sensitivity
supply voltage as the power line voltage fs varied
Set SYNC switch to EXT
between 103 and 127 volts. All regulated voltages TRIGGER LEVEL to AUTO
should remain within *l% over this line voltage Horizontal AC-DC switch to DC
range.
VERT PRESENTATION control to A or B
5) Measure the ripple voltage on the various sup- Trigger Sensitivity Control, R247, fully
counterclockwise.
plies. They should approximate the values given
in Table 4-5 with the line voltage at 115 volts. Connect a 250 kc sine wave of 0.7 v rms to the
SYNC (right-hand) terminals. With an oscilloscope
6) Measure cathode-ray tube cathode voltage as observe the square wave by clipping the oscilloscope
instructed in paragraph 4-5C. If necessary R308, probe over the body of R204 (V201A plate resistor).
H. V, Adjustment, can be adjusted to set this Increase Trigger Sensitivity control R247, until
voltage to -2250 volts. If this adjustment is stable triggers are obtained. Check trigger sensi-
changed, recalibrate the horizontal and vertical tivity from 50 cps to 250 kc. Stable triggering
amplifier gain. should be obtained with less than 0.7 v rms over this
range. Remove the test set-up and check the rate
7) Adjust FOCUS control for best focus and set when the TRIGGER LEVEL control is in AUTO
ASTIGMATISM control, R316, for a small, round, position--should be about 120 *50 cps. |
ACEC
