Operating Instructions — Type B
capacitor is located in the probe body in the P405, P410,
P420, and in the termination block at the instrument end of
the cable in the P450, P450-L and P410Q. It takes only a few
seconds to check this adjustment, and it is a good practice
to make this check each time the probe is to be used. Sim
ply touch the probe to the oscilloscope calibrator-output
terminal and observe the calibrator waveform on the screen.
If necessary, adjust the trimmer for a fla t top on the cali
brator square wave. For critical adjustment of the P4100,
a faster-rising square wave, such as the output of the Tek
tronix Type 104A or Type 105, should be used.
Preventative Maintenance
Regular inspection of the nose and cable fastening screws
w ill help prevent possible mechanical damage due to
twisting. A small nylon screw holds the nose in place, and
an alien setscrew grips the cable firm ly. Tighten these screws
if they work loose.
Probe Repair
To disassemble, remove the nylon screw and loosen the
alien setscrew. Slide the probe body back over the cable.
Examine the layout carefully before proceeding. The cen
ter conductor of the cable is extremely fragile— be careful
not to break it when removing a probe part. Replacement
parts can be obtained through field offices or directly from
the factory. When resoldering, it is important to get a good
connection between the probe resistor and the center con
ductor of the cable. Reassemble the probe and tighten the
screws.
Coupling
It is sometimes unnecessary or undesirable to display the
dc level of the waveform. In the two AC positions of the
INPUT SELECTOR switch, a capacitor in series with the
input blocks the dc component of the waveform so that only
the ac component is displayed.
Deflection Sensitivity
The VOLTS/CM switch inserts frequency-compensated at
tenuators ahead of the amplifier. The VARIABLE control
provides continuous adjustment of the deflection sensitivity
between the values indicated by the VOLTS/CM switch.
NOTE
The VARIABLE control must be clockwise to CALIBRAT
ED position for the sensitivity to be as indicated by the
VOLTS/CM control.
Gain Adjustment
Aging of tubes w ill affect the gain of the plug-in unit.
After the plug-in unit has been in use for a period of time
the gain adjustment should be checked. Display a calibrator
waveform of 0.2 volts peak to peak with the VOLTS/CM
switch in the .05 position. Adjust the G A IN ADJ. 1 control
until the displayed waveform is four graticule divisions in
amplitude. Be sure the VARIABLE control is turned clock
wise to the CALIBRATED position before making this ad
justment.
Now set the calibrator at 20 MILLIVOLTS and turn the
VOLTS/CM switch to .005. Adjust the G A IN ADJ. 2 con
trol until the amplitude of the displayed waveform is four
divisions.
DC Balance Adjustment
The need for adjustment of the DC BAL control is indi
cated by a shift in the position of the trace as the VARIABLE
control is rotated. This is caused by tube aging and the
resultant shift in operating potentials. This adjustment should
be made after the G A IN ADJ. control is set. Rotate the
VARIABLE control back and forth and adjust the DC BAL.
control until the trace position is no longer affected by ro
tation of the VARIABLE control.
Positioning Adjustment
The VERT POS RANGE control balances the dc output
level so the full range of the front-panel positioning control
can be utilized. The VERT POS RANGE control is located at
the left to the rear of the plug-in unit and is accessible
when the left side panel is removed. Center the VERTICAL
POSITION control. Adjust the VERT POS RANGE control
to center the trace on the screen.
2-2
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