HP 120A - Page 44

Sect. IV Page 4
Figure 4-1. Most Internal Calibration Controls arc Located In An Easily-Reached
Row Along Side of Chassis.
(See also Figure 4-2.).
b. Stability Adjustment
Set VERT. SENSITIVITY to CAL.
SWEEP TIME to 0. 5 MILLISECONDS
SYNC to INT.
TRIGGER LEVEL to AUTO.
Connect '$,410 B (-100v range) to pin 8 V203. Rotate
Sweep Stability Control, R228, ccw until sweep is
triggered, then back off until it just stops. Take a
voltage reading which should be about -72 volts. Now
connect a clip lead from pin 1 V201 to ground. Slowly
rotate R228 ccw until the sweep starts free-running,
then back off until it just stops. Take a voltage read 
ing which should be about -78 volts. The difference
between these two readings is the amplitude of the
triggers and must be between 5 and 7 volts. While
the triggers are shorted (clip lead from pin 1 V201
to ground) set R228 to 2. 0 volts more positive than
the last reading. This is the proper setting for the
stability control.
c. External Trigger Sensitivity
Set SYNC switch to EXT.
TRIGGER LEVEL to AUTO.
Horizontal AC-DC switch to DC.
Connect a 10 kc sine wave of 0. 3v rms into the SYNC
terminals. With a 10:1 or better a 50:1 probe and os 
cilloscope observe the output triggers from the Trig 
ger Generator as you increase the Trigger Sensitivity
control R247. Increase trigger sensitivity until stable
triggers are obtained. Check trigger sensitivity from
50 cps to 250 kc. Stable triggering should be obtained
with less than 0. 5v rms over this range. Check the
rate when the control is in the AUTO, position --
should be about 120 ±50 cps.
d. Sync Polarity
Set TRIGGER LEVEL to AUTO.
VERT. SENSITIVITY to 1 VOLTS/CM
Feed 2v rms of Ike sine wave into the Vertical Am 
plifier and into the sync, terminals (right-hand ter 
minals on the front panel). Switch SYNC switch to
INT - first, and then to EXT. The first half cycle
should be negative going in each case. Switch to
INT+ and it should be positive going.
e. TRIGGER LEVEL
Set SYNC switch to INT+