Tektronix TYPE L Instruction Manual page 21

be investigated to
components.
When the grids of the Phase Inverter Stage
are shorted together, the effect of the vertical
positioning controls must be considered.
addition to the VE R TIC AL POSITION control,
the Vert. Pos. Range
the VARIABLE ATTEN. B AL. control (R6812)
have a pronounced effect on the vertical beam
positioning. An improper adjustment of either
o r both of these controls can result in a loss
o f the trace.
There is a possibility that the loss of trace
may be due to a defective tube-heater circuit.
This condition can be determined by observing
the tubes in the plug-in unit for heater glow.
If no glow is observed, it w ill most likely be
caused by an open heater in one or more
of the tubes. Other possibilities, however,
are shorted capacitor C6952, or a defective
resisto r at the low end of the string.
2. In ability to position the trace
If the trace is visible on the crt, but it
cannot be moved with the VE R TIC AL POSITION
control, some defect that is rendering this
control inoperative is indicated. If the trace
can be moved with the Vert. Pos. Range con­
tr o l, the V E R TIC AL
probably defective.
moved with the Vert.
however, the trouble w ill lie in some circuit
following the Phase Inverter Stage. The trouble
could be an open H.F. Peaking control, R6692,
o r short between correspondingly-opposite sides
o f the am plifier. An examination of the lead
dress, or a continuity check with an ohm-
m eter, w ill reveal the shorted condition.
3. No vertical deflection
If the horizontal trace is present on the
c rt, but the vertical signal is not displayed,
an open circuit somewhere
deflection system is indicated. However, since
the horizontal trace is present, the defective
component is one that does not upset the dc
balance.
If the trouble is
am plifier, the defective component is in the
circuit of either the F irs t Am plifier (V5942)
o r the Second Am plifier (V6042). Since these
stages are ac-coupled to
AA
locate the defective
control (R6572) and
POSITION control is
If the trace cannot be
Pos. Range control,
in the vertical
originating in the X10
the Second C.F.
Maintenance - Type L Plug-In
stage, an open circuit ahead of the coupling
capacitor w ill not affect the dc balance.
If the trouble
am plifier section, it can be isolated to either
In the Phase Inverter Stage or the Output Stage
with the VERTICAL POSITION control. If the
trace can be moved vertically, a defect in
the Phase Inverter Stage is indicated.
could be an open resistor in the cathode circuit,
o r an open screen divider. If the trace cannot
be moved with the VERTIC AL POSITION control,
the H.F. Peaking control (R6692) in the Output
Stage is probably open.
4. Insufficient vertical gain
If the vertical deflection on the crt no longer
corresponds to the calibrated value, a change
in the gain characteristics of the plug-in unit
is indicated. If the change in gain is very
slight, as w ill usually be the case, the unit
can be recalibrated according to the instructions
presented in Calibration Procedure. If there
is a considerable change in gain, however,
a change of tubes or circuit components will
be required.
If only the X10 am plifier is out of ca li­
bration, the F irs t- or Second-Amplifier stage
is probably at fault. Two adjustments associated
with these stages, the V6042 Cathode-Current
Adj (R5922), and the X10GAIN ADJUST (R6052),
are very important. Refer to the Calibration
Procedure for the proper adjustment of these
controls.
If the main am plifier section is out of c a li­
bration, the Phase Inverter Stage is probably
at fault. It is important to note that the 12AU6
tubes in this stage are selected and paired
fo r filament voltage and grid bias.
Unstable operation may be encountered if
standard 12AU6 tubes are used as replacements.
An open VARIABLE
greatly decrease the gain of the Phase Inverter
Stage. A change in the value of the cathode
resisto rs, or in the value of the screen divider,
can also affect the gain.
5. W aveform Distortion
If waveform distortion occurs, firs t check
to see which positions of the VOLTS/CM switch
have distortion. If the distortion occurs on one
is originating in the main
control (R6352) w ill
This
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