Calibration— Type M
4. Check Input Coupling Capacitor for Leakage (All
Channels)
NOTE
A
lower dc voltage can be used to make this check
if a voltage as high as 500 volts is not applied
during normal use of the plug-in unit. If a lower
voltage is used when performing this check, trace
displacement will be less by a direct proportion.
For example, if the + 100-volt regulated power
supply is used as the dc source, trace displacement
should be less than Vs of 2 centimeters or 4 mm.
Set Channel A MODE switch to AC NORM and position
the trace to the center graticule line. Connect the connector
adapter to the Channel A input connector and connect a
long test lead to the adapter. The test lead should be about
4' long, or sufficiently long to reach a + 500-volt source such
as the oscilloscope +500-volt regulated power supply. Touch
the test lead to +500 volts. Check the amount of shift after
the trace returns to the screen. Trace displacement should
be less than two centimeters from the original position.
Remove the test lead from +500 volts and set the Channel
A MODE switch to OFF. Disconnect the adapter with the
test lead from Channel A.
Repeat this step for the other channels. Then disconnect
the test lead from 500 volts and remove the adapter. Set all
MODE switches to AC NORM.
5. Check Push-Pull Balance (All Channels)
This step checks the push-pull balance of Q5324 and
Q5334 in each channel. If the beta of the transistors closely
match each other, trace shift will not exceed the follow
ing limit. To make the check, adjust all POSITION controls
to position the traces to the vertical-system electrical center.
Then set each MODE switch to AC INV. and note the
amount of trace shift.
Each trace should not shift more than three centimeters
from the original position. Since the test oscilloscope has
a vertical scan of 4 centimeters or ± 2 centimeters and the
trace shift limit is ± 3 centimeters from vertical-system
electrical center, it is possible for the trace to move out
of visibility but still be within the trace-shift limit. Note
the degree of rotation of the POSITION control required to
position the trace back to the original position and compare
this with a known degree of rotation required to move the
trace three centimeters. Typical rotation distance is 50°.
6. Check Output DC Level
Set all MODE switches to AC NORM, and position all
traces to the vertical-system electrical center. Measure the
voltage between pin 3 of V5383 and ground, and between
pin 8 of V5383 and ground. These voltages should meas
ure between 65 and 70 volts and the readings should be
within a fraction of a volt of each other. Readings within
these limits indicate proper input dc levels to the oscilloscope
vertical amplifier.
Disconnect the VOM.
7. Check for Excessive Grid Current (All Channels)
This step checks the Input Cathode Follower V5323 of
each channel for excessive grid current, under no-signal
conditions.
To make the check use three short patch cords (6” long)
to connect the four inputs together, and use a fourth patch
cord to ground the inputs. Set the channel A MODE switch
to DC NORM, and the VOLTS/CM switch to .02. Observe the
vertical shift of the trace. The trace should not shift more
than two millimeters. Repeat the procedure for channels B,
C, and D. If the trace for any channel shift more than two
millimeters, replace V5323 and repeat steps 2, 3, 5, 6 and 7.
8. Check for Microphonics (All Channels)
This step checks for excessive microphonics in V5323.
To check for ringing type of microphonics, start with
channel A by setting its MODE switch to AC NORM, and
set the MODE switches for the other channels to OFF. Set
the oscilloscope Time/Cm switch to 1 Millisec and tap
lightly on the front panel of the M Unit. Microphonics
should not exceed one centimeter. Set the channel A MODE
switch to OFF and check the remaining channels in the
same manner.
9. Check ALTERNATE Operation
This check tests the Four Channel Switching Circuit for
proper alternate-mode of operation.
Set all MODE switches to AC NORM, and position the
traces about one centimeter apart with the POSITION
controls. Check that each time the sweep is triggered,
the trace runs sequentially from channel A through D with
various settings of the oscilloscope Time/Cm switch. After
completing this step, disconnect all patch cords.
10. Check CHOPPED Operation
The first part of this step checks the Switching B.O.
(Q6350) for proper free-running operation. The second part
checks the diode gates for proper match and turn off.
(a) Check the Swiching B.O. by setting the oscilloscope
Time/Cm switch to 1
fiSEC
and the M-Unit ALTERNATE/
CHOPPED switch to CHOPPED. Check the waveform for
approximately a 250-kc chopping rate. (Waveform appears
similar to the one shown in Fig. 2-2 when the traces are
positioned the same distance apart.)
(b) Check the gating diodes by setting the oscilloscope
Time/Cm switch to 1 Millisec. Check the width of all
traces at normal intensity. The trace width should not ex
ceed 1.5 millimeters. If a trace is wider than 1.5 millimeters,
check the reverse resistances of diode pairs (D5345 and
D5347, and D5346 and D5348). The resistance readings for
each pair should be approximately the same to obtain
proper dc-level match and minimum trace width.
11. Gain Adjustment (All Channels)
Set the ALTERNATE/CHOPPED switch to the ALTERNATE
position and all MODE switches to DC NORM. Make sure
all VAR. GAIN controls are set to CALIB. Set the oscillo
scope Time/Cm switch to .5 Millisec and the triggering Mode
switch to Auto. Apply a 20-millivolt signal from the oscillo
scope Amplitude Calibrator to the channel A input con
nector. Set the channel A GAIN ADJ. to obtain exactly
one centimeter of deflection.
Repeat the procedure for each of the other channels.
After completing the adjustment for channel D, leave the
signal connected to that channel.
5-4
®2
