Vertical Gain Adjustment; Input Signal Connections - Tektronix 1S1 Instruction Manual

2. Set the DC OFFSET control for zero volts at the OFF-
SET OUTPUT jack.
3. Set the mVOLTS/CM switch to 200.
4. Turn the mVolts/Cm VARIABLE control clockwise to the
point of maximum sensitivity.
5. With the VERT POSITION control, position the free-
running trace to the horizontal centerline.
6. Return the mVolts/Cm VARIABLE control to the CAL
detent position.
7. With a small screwdriver, adjust the front-panel VAR
BAL control to return the trace to the horizontal centerline.
8. Repeat steps 4, 5 and 6 to check the adjustment.
9. Leave the mVolts/Cm VARIABLE control set to the CAL
position.
Vertical Position Range Adjustment
With the dc offset at zero volts and with no signal applied,
if the VERT POSITION control does not have enough range
to move the trace off the screen in one direction or the other,
the position range control may need to be adjusted. First,
however, check the 3 balance adjustments given above. If
the balance adjustments are correct but the range of the VERT
POSITION control is not correct, make the adjustment as
follows:
1. Set the DC OFFSET control for zero volts at the OFF-
SET OUTPUT jack.
2. Center the VERT POSITION control so that the white
dot points straight up.
3. Locate the POSITION RANGE adjustment control (R194)
shown in Fig. 2-4.
4. Adjust R194 to position the free-running trace to the
horizontal centerline.

Vertical Gain Adjustment

The vertical gain of the Type 1S1 should be adjusted when
the unit is first installed in an oscilloscope and should be
checked occasionally thereafter.
The use of a 50-ohm amplitude calibrator, as described in
the calibration procedure in Section 5, is recommended for
this adjustment. The procedure given there provides an
accuracy within about 1%.
Another method of checking the vertical gain can be used
if the oscilloscope 1-kc calibrator has a position that is cali-
brated into 50 ohms (e.g. 0.1 V Into 50
position). However, since the calibrator tolerance is ±3%,
accuracy of the check with the oscilloscope calibrator will
be only within about 4%, unless the amplitude error is known.
The following procedure is suggested for use of the 0.1 V
Into 50 calibrator signal:
1. Set the TIME/CM switch to 50 µsec.
2. Connect the oscilloscope calibrator directly to the
Type 1S1 SIGNAL IN connector through an adapter and a
coax cable.
3. Set the calibrator to the 0.1 V into 50
4. Set the Type 1S1 mVOLTS/CM switch to 20.
5. Trigger the crt display with the TRIGGER SENSITIVITY
control.
6. Check for 5cm of vertical deflection (see Fig. 2-5).
If the amount of error in the calibrator signal is known, check
the display for a vertical deflection of 200mv/cm.
Fig. 2-5. Typical oscilloscope display for checking vertical
deflection factor ( 4%) with oscilloscope calibrator.
7. If the vertical gain is not correct, use a small screw-
driver to adjust the front-panel VERT GAIN control.
Loop Gain Adjustment
To present a correct display on the crt screen when using
a low dot density, the dot transient response of the sampling
channel must be correct. That is, the gain of the sampling
feedback loop must be set so that each display dot ac-
curately represents the signal level at the time the sample
was taken. If loop gain is greater than unity (gain of 1),
the display will be excessively noisy and have overshoot.
If loop gain is less than unity, the rising portions of fast
pulses will be rolled off when using a low dot density, and
the display amplitude will be decreased for sine waves.
In the Type 1S1, loop gain is adjusted to unity with the
SMOOTHING control set to the fully clockwise NORM posi-
tion. The SMOOTHING control can then be used to decrease
loop gain when necessary to reduce display noise.
Use a 1-volt 40-kc fast-rise pulse approximately 20 nsec
in duration, as described in the calibration procedure, for
at the .5 Volts
checking loop gain. This check causes the loop to process
a 1-volt change between each two samples, thus detecting
any variation from unity gain.
General Information
The input circuits for both the vertical signal and the
external triggering signal are designed to have the character
Operating Instructions – Type 1S1

INPUT SIGNAL CONNECTIONS

position,
2-9