Tektronix Type Z Instruction Manual page 21

Maintenance — Type Z
transistors in all cathode follower and amplifier stapes,
preferably by substitution. After substituting a part, vari ­
ous adjustments are affected.
cedure in the Calibration section for a guide in setting up
the front-panel controls, and perform steps 2, 5, 6 and 7
in the Calibration procedure to determine if any of the
adjustments given in those steps require readjustment.
When a tube or transistor is replaced in a stage, imbal ­
ance may occur. Choose matched components or use Tek ­
tronix parts to get the trace onto the screen. To aid in
determining how well the stage balances, refer to the
Calibration section for the appropriate balance step to
perform and the location of jumper-connection test po nts
(see Fig. 5-3) to use.
If the trouble has still not been corrected, apply a known
input signal and use a test oscilloscope to check the gain
of each stage. The overall gain of the unit as measured
at the cathode of each output cathode follower should be
1 (single-ended); the push-pull gain should be 2. The input
cathode followers should have a single-ended gain of
approximately 0.99, the differential amplifier a gain of
approximately 0.7, the output amplifier a gain of approxi ­
mately 2.6, and the output cathode follower measu r ed
from the input grid to output a gain of approximately 0.98.
The single-ended gain of the entire output cathode 'ol-
lower stage when measured from the collector of the out ­
put amplifier to the cathode of the output cathode fol ­
lower is approximately 0.6.
It should be remembered when measuring the gain t h at
the input of the differential amplifier is single-ended while
the output is push-pull. The input of the differential ampli ­
fier is measured at the grid of either V7634 or V8634, as
applicable. Output of the stage is measured at the plate
of each tube. Then the single-ended gain of each half
of successive push-pull stages should be checked for proper
gain as given in the previous paragraph.
time check to see if the gain for each half of the push-pull
stage is approximately the same.
When the defective stage has been found, use voltage
and resistance measurements to determine the exact cause
of the trouble.
2. Nonlinearity
An improper setting of the OUTPUT CF BAL. adjustment
causes nonlinear operation and the trace to be deflec'ed
off the screen. An operator can easily correct for the de ­
flected trace symptom if the OUTPUT CF BAL. adjustment
had not been moved more than about 20° from eitner
side of the correct setting.
Instructions section for centering the trace, the AMP. DC
BAL. adjustment is used to position the trace behind the
horizontal centerline of the graticule when the PO ITION
control is set to midscale.
not be corrected unless the OUTPUT CF BAL. is brought
back to its correct setting.
To check if nonlinearity exists, proceed as follows:
Apply a 100-mv calibrator signal to the A input con ­
nector. et the A AC-DC switch to DC, the A VOLT /CM
switch to .05, and the Mode switch to A-Vc.
ity switch to +, the Range switch to 1 V, the Helidial
4-4
Use the Preliminary Pro ­
At the same
As stated in the Operat ng
However, the nonlinearity will
et the Polar ­
control to 0.00, and the PO ITION control to midscale.
et the oscilloscope triggering controls to produce a stable
display. Rotate the Helidial slowly clockwise to position
the signal to the center of the graticule. Note the exact
amplitude of the signal (should be about 2 cm high.)
Rotate the Helidial slowly clockwise to position the signal
to the bottom 2 cm of the graticule. Note the amplitude
of the signal. Place the Polarity switch to — and position
the signal to the top 2 cm of the graticule. Note the ampli ­
tude again. If changes in signal amplitude are noted which
are greater than any slight inherent compression (if any)
due to the main oscilloscope vertical amplifier or crt, then
the Z Unit is operating in a nonlinear region.
To restore the Z Unit to proper operation, perform steps
2. 5 and 6 in the Calibration procedure.
liminary (Calibration) Procedure for a guide in presetting
the front-panel controls prior to making the adjustments.
3. Low Differential Rejection Ratio
The differential rejection ratio is highest on the .05 settings
of the VOLT /CM switches; the ratio is lower on other
settings due to slight imbalances in the input attenuators.
If the differential rejection ratio seems normal on the .05
settings of the VOLT /CM switches but abnormal on one or
more of the other ranges, the input turret attenuators
should be checked.
If the differential rejection ratio (.05 volts/cm) is less than
the specified 40,000 to 1, check the setting of the DIFF.
BAL. potentiometer. Then check the tubes and transistors
in all cathode follower and amplifier stages (by substitu ­
tion). Apply the same signal first to one and then the
other input connector of the unit. The vertical deflection
produced should be the same in either case with only the
polarity reversed. If the deflection produced by the signal
applied to one input is different than the deflection pro ­
duced by the same signal applied to the other input, a
difference in gain exists between the two sides of the ampli ­
fier. Use a test oscilloscope to determine where this gain
imbalance is introduced. When the defective stage has
been determined, use voltage and resistance measurements
to find the cause of the trouble.
4. Large DC mbalance
A large d c imbalance in the preamplifier will cause the
oscilloscope trace to deflect off the screen, and the PO I ­
TION control may not have sufficient range to bring the
trace back on the screen.
switch to TE T, center the PO ITION control, and use the
AMP. DC BAL. adjustment to attempt to bring the trace
back on the screen. If the trace does not appear, perform
steps 2 through 6 in the Calibration section of the manual.
When the adjustments and jumper connections are made
as instructed in the previous paragraph, there may be one
jumper-connection checkpoint where the trace cannot be
made to return to the screen. When this occurs, the stage
following the jumper (looking toward the output of the
unit) is producing the imbalance.
transistors, whichever apply, plus voltage and resistance
measurements will determine the cause of the imbalance.
When substitutions are made, repeat steps 2 through 6 as
Use the Pre ­
If this occurs, set the Mode
ubstitution of tubes and