HP 120A - Vertical Amplifier

Sect. IV Page 5
Adjust input for 8 cm of deflection. Rotate TRIGGER
LEVEL control clockwise and see that the starting
point of sweep moves upward. The range of this con 
trol should be at least + 2cm from the average value
of the signal. Switch SYNC switch to EXT. Adjust in 
put signal for 20v peak-to-peak. Range of TRIGGER
LEVEL control should exceed this signal.
f. Internal Trigger Sensitivity
Set SYNC switch to INT+
SWEEP TIME switch to 50 MICROSECONDS/
CM
Vertical AC-DC switch to DC
With a 10 kc sine wave fed into the Vertical Amplifier,
decrease the input to the point where the triggers are
becoming unsteady (observe triggers as above). Ver 
tical deflection should be less than 0. 4 cm when the
triggers become unsteady. Check triggering from 50
cps to 250 kc.
g. Trigger Level Sensitivity
Repeat tests in the two previous paragraphs using
TRIGGER LEVEL control (tune for maximum sensi 
tivity). Check using same sensitivity specifications
over range from 10 cps to 250 kc.
h. Line Synchronization
Set SYNC switch to LINE
TRIGGER LEVEL to AUTO.
The normal 60 cycle pickup in Vertical Amplifier
should give a stable pattern.
4-10 VERTICAL AMPLIFIER
a. Balance
Set VERT. SENSITIVITY control to 10 VOLTS/CM
HOR. SENS, control to 10 VOLTS/CM
Turn VERT. SENSITIVITY VERNIER full counter 
clockwise and position spot to center with VERT.
POS. control. Turn VERNIER clockwise and re 
position spot to center with VERT. DC BAL. con 
trol. Repeat this sequence until there is no move 
ment of spot as VERNIER is rotated. Set VERT.
POS. control to the center. Spot should now be on
the screen.
b. Set Gain
Set VERT. SENSITIVITY to 10 MILLIVOLTS/CM
VERT. SENSITIVITY VERNIER to CAL
With 100 millivolts peak-to-peak from a Voltmeter
Calibration Generator set Vertical Amplifier VERT.
GAIN control to give exactly 10cm of deflection. Check
this setting at high and low line voltage.
c. Calibrator
Set VERT, SENSITIVITY switch to CAL
VERT. SENSITIVITY VERNIER control to CAL
SWEEP TIME switch to 2 MILLISECONDS/CM
Check deflection polarity by varying R356. The top
of the calibrator square wave should move. Set R356
for 6. 0cm of calibrator deflection. Check symmetry-
should be 40-60% or better.
d., DC Shift, Hum and Microphonics
Set vertical (left) AC-DC switch to DC
VERT. SENSITIVITY switeh to 10 MILLIVOLTS/
CM
VERT. SENSITIVITY VERNIER control to CAL
HORIZ. SENSITIVITY switch to 10 VOLTS/CM
Short input. Switch input from DC to AC. The spot
should shift not more than 0. 2cm. There should be
no distortion of the spot due to hum or ripple. Re 
move short and apply open shielded 3/4 ” plug. Check
again for spot distortion. When jarring the 120A with
a shorted input there should be no vertical instability
greater than l/2cm. Switch from HOR. SENS, posi 
tions to SWEEP TIME positions on the SWEEP TIME
HOR. SENS, switch. The spot should not move ver 
tically more than 0. 1cm.
e. Compression
Set VERT. SENSITIVITY switch to 10 MILLI 
VOLTS/CM
VERT. SENSITIVITY VERNIER to CAL
Connect an insulated (J)400D across the vertical de 
flection plate terminals. CAUTION HIGH VOLTAGE !
Switch to 1 volt range on the 400D. Apply Ike signal
to vertical input terminals and adjust output of signal
generator for a reading of . 95v on the 400D when spot
is positioned to the center of screen. Position the spot
to top line of the graticule and read 400D. Position
the spot to bottom line of graticule and read 400D .
The difference of each reading from the reference
. 95volts is the compression in percent. Compression
should be less than 6%.
f. Square Wave Response
Set VERT. SENSITIVITY switch to 10 MILLI 
VOLTS/CM
VERT. SENSITIVITY VERNIER control to CAL
SYNC switch to INT+
TRIGGER LEVEL control to AUTO.
SWEEP TIME control to 10 MICROSECONDS/
CM
Apply 50 kc square wave to vertical input terminals.
Adjust generator for 8cm deflection. Adjust C15 for
best square wave response. A maximum of 2% over 
shoot is permitted.
g. Attenuator Compensation
Set VERT. SENSITIVITY to 100 MILLIVOLTS/CM
VERT. SENSITIVITY VERNIER to CAL