Calibration—221 Service
POWER SUPPLY
Equipment Required
1. Digital voltmeter
3. 1:2 power step-up transformer
2. Variable auto transformer
4. Three-inch screwdriver
Control Settings
Preset the controls as given in the Preliminary Control
Setting.
1. Check/Adjust Low-voltage Supply
a.
Connect the digital voltmeter from the —5 volt test
point to the +5 volt test point.
b.
Use the variable auto transformer and 1:2 power
step-up transformer to provide a 90 to 250 Vac line source.
Connect the 221 oscilloscope to the line.
c.
Check for a reading of 10 volts from a 90 to 250 Vac
line.
d.
Adjust R644 Low Voltage adjustment for exactly
10 volts. See Fig. 5-1.
e.
Connect the common lead of the digital voltmeter to
the 0 volt test point.
f. Check the +5 volt supply for +5 volts ±50 mV
2.
Check/Adjust High-voltage Supply
a. Connect the digital voltmeter to the 1 kV test point.
b. Check fo r a reading of —1000 volts.
c. Adjust the High Voltage adjustment R662 for exactly
—1000 volts. See Fig. 5-1.
3.
Check/Adjust Grid Bias
a. Connect the digital voltmeter to the 0.2 volt test
point.
b. Rotate the INTENSITY to the fu lly clockwise
position.
c. Check the digital voltmeter fo r a reading of 0.2 volt
±0.02 volt.
d.
Adjust Grid Bias Adjustment R739 fo r exactly
0.2 volt. See Fig. 5-1
4.
Check +48-volt and +75-volt Supplies
a. Connect the digital voltmeter from the 0 volt test
point to the +48-volt test point (leave INTENSITY fu lly
clockwise fo r remainder of Step 4).
b. Check fo r a minimum of +48 volts.
c.
Connect the digital voltmeter from the 0-volt test
point to the +75 volt test point.
d. Check fo r a minimum of +75 volts.
e. Set INTENSITY as desired for normal viewing in
Step 5.
5-4
REV B, MAY 1978
