Tektronix 535A, Instruction Manual

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Maintenance —Type 535A
CIRCUIT TROUBLESHOOTING
Although the Type 535A is a complex instrument, it can
be thought of as consisting of eight main circuits, in addi­
tion to the Calibrator circuit. These are the:
1. Low-Voltage Power Supply.
2. CRT Circuit and High-Voltage Power Supply.
3. Vertical Amplifier and Delay Line.
4. Time-Base "A" Trigger Circuit.
5. Time-Base ”B" Trigger Circuit.
6. Time-Base "A" Generator.
7.
Time-Base 'B" Generator.
8. Horizontal Amplifier.
The first circuit to check, for practic ally any type of trouble,
is the Low-Voltage Power Supply. Because of the circuit
configuration employed, it is possible for an improper power
supply voltage to affect one circuit more than the others.
For
example, if the gain of the Vertical Amplifier should
decrease slightly, while the other circuits appear to be func­
tioning normally, this could be due to an improper supply
voltage and not to any condition originating in the Vertical
Amplifier. In cases of this type, valuable time can be saved
by checking the power supply first.
On the other hand, the crt display can often be used to
isolate trouble to one particular circuit when trouble ob­
viously exists in that circuit. If there is no vertical deflec­
tion, for example, when the intensity and horizontal de­
flection appear to be normal, it is apparent that an open
condition exists in the Vertical Amplifier and this circuit
should be investigated first.
Front-Panel Checks
The following front-panel checks will help you to isolate
the trouble in an instrument to a given circuit. The inter­
relation between circuits is such that these checks arc not
always completely accurate in isolating a trouble to a given
circuit. If you are unfamiliar with the instrument these front­
panel checks may prove helpful in starting to look for
trouble.
Before attempting any of the following front-panel checks
make sure that the plug-in installed in the instrument is
operating correctly. If the pilot lamp fails to light when the
POWER switch is turned to the ON position, and if the fan
fails to operate, turn to the section on troubleshooting the
Low-Voltage Power Supply. If the pilot light and fan both
operate but the Time-Delay Relay fails to operate with an
audible 'click'' after one minute you should also consult the
section on Troubleshooting the Low-Voltage Power Supply.
With an operating plug-in installed, and the pilot light
and fan both operating, allow the oscilloscope to run for
several minutes. Set the front-panel controls as follows:
STABILITY full right (clockwise)
TRIGGERING LEVEL 0
TRIGGERING MODE
AC
TRIGGER SLOPE I INT.
VARIABLE (TIME/CM) full right
TIME/CM 5 MILLISEC
HORIZONTAL DISPLAY
A
FOCUS mid-scale
INTENSITY full-left (counterclockwise)
ASTIGMATISM mid-scale
SCALE ILLUMINATION mid-scale
HORIZONTAL POSITION mid-scale
VERNIER mid-scale
The settings of other controls are not critical at this time.
If your are using a Type TU1 or TU2 Test-Load Plug-In
Unit set the toggle switch to the 1:1 position and the
AMPLITUDE CALIBRATOR switch to the .2 VOLTS position.
If using another type of plug-in set the VOLTS/CM switch
to 1 volt and the AMPLITUDE CALIBRATOR switch to 2
VOLTS
Using a patch cord which introduces no attenuation con­
nect the CAL. OUT connector to the INPUT connector of the
plug-in preamplifier. Advance the INTENSITY control to the
mid-scale position.
Now examine the face of the crt. If no display is evident
examine the Beam-Position Indicator lamps. If the display
is positioned off the screen vertically turn the VERTICAL
POSITION control from one extreme position to the other,
watching the face of the crt as you do so. If no display
appears, and operation of the VERTICAL POSITION control
has no effect on the Beam-Position Indicator lamps turn to
the section on Troubleshooting the Vertical Amplifier.
If the display which appears consists of a horizontal line,
you may check the operation of the calibrator by removing
the end of the patch cord which is inserted into the CAL.
OUT connector and holding it in your hand. A series of
sloping vertical lines appearing on the crt indicate that the
Vertical Amplifier is operating, and that the Amplitude Cali
brator is probably inoperative. See the section on Trouble­
shooting the Amplitude Calibrator for the remedy.
If the operation of the VERTICAL POSITION control causes
the vertical Beam-Position Indicator lamps to indicate the
display as centered, rotate the HORIZONTAL POSITION
control from one extreme position to the other. If the hori­
zontal Beam-Position Indicator lamps still indicate the dis­
play is off the screen refer to the section on Troubleshooting
the Horizontal Amplifier.
If both sets of Beam-Position lamps indicate that the dis­
play is centered, but no display is observed, CAUTIOUSLY
advance the INTENSITY control. Watch for a display to
appear on the screen. If no display is seen or if the dis­
play is of low intensity but otherwise normal, refer to the
section on Troubleshooting the CRT Circuit.
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