Tektronix 503, Instruction Manual

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Maintenance— Type 503
Insufficient Vertical Deflection, Waveform Dis­
tortion, or Low Differential Input Rejection Ratio
These troubles are a ll caused by a defective vertical
amplifier. Refer to the Circuit Troubleshooting section of
the Troubleshooting procedure.
Insufficient or No Horizontal Deflection
Either of these conditions can be produced by the Sweep
Generator or the Horizontal Amplifier. If the sweep is
shortened but the timing is not affected, the trouble is prob­
ably in the Sweep
Generator. If both the sweep length
and the timing are affected, the trouble is probably in the
Horizontal Amplifier.
As an additional check to determine which circuit is defec­
tive, place the HORIZONTAL DISPLAY switch in the HORIZ.
AMPLIFIER position. Set the HORIZONTAL SENSITIVITY
switch to the .1 VOLTS/CM position and the VARIABLE
control fully clockwise. Connect the 500 mV calibrator sig­
nal to the +IN P U T connector of the horizontal channel.
Two dots, spaced 5 cm apart, should appear when the
positioning controls are adjusted. If the deflection is cor­
rect, the trouble is probably in the Sweep circuit. If the
deflection is not correct, the trouble is in the Horizontal
Amplifier.
Nonlinear Horizontal Sweep
The linearity of the horizontal deflection can be checked
by connecting a marker generator or the calibrator output
to a vertical input of the oscilloscope. If the sweep is linear,
the markers or the calibrator waveform w ill be spaced
equidistant along the sweep. A nonlinear sweep can be
caused by either the Sweep Generator or the Horizontal
Amplifier.
To determine which circuit is defective, place the HORI­
ZONTAL DISPLAY switch in the HORIZ. AMPLIFIER position.
Set the HORIZONTAL SENSITIVITY control to .5 VOLTS/CM
position and the VARIABLE control fully clockwise. Connect
the 500 mV signal from the CAL. OUT connector to the
+ INPUT connector of the Horizontal Channel.
Two dots, spaced 1 cm apart, should appear when the
positioning controls are ajusted. If the spacing between
dots remains the same as they are moved across the screen
with the HORIZONTAL POSITION control, the nonlinearity
is probably in the Sweep Generator. If the spacing between
dots varies, the trouble is in the Horizontal Amplifier.
Improper Sweep Timing
If the timing is o ff in some, but not all, positions of the
SWEEP TIME/CM switch, one o f the timing resistors or timing
capacitors has changed in value. A check of the Timing
Switch diagram w ill show which components are common to
these positions, and will assist in pinpointing the defective
components.
If the timing is off in all positions of the SWEEP TIME/CM
switch, the Horizontal Amplifier is probably the circuit at
fault. However, it is imoprtant that the power supply volt­
ages be checked. Check to see if the timing circuits can be
calibrated in accordance with the instructions presented in
the Calibration section of this manual. If the circuits cannot
be adjusted for correct timing, refer to the section on trouble­
shooting the Horizontal Amplifier.
Improper Triggering
If the waveform observed cannot be triggered (locked
into position) properly, the trouble can be misadjustment of
the STABILITY control or malfunction of some other part of
the Sweep circuit or the Trigger circuit.
Check the adjustment of the STABILITY control as
described in the Calibration section of this manual. If the
trace can be turned on and off by rotating the LEVEL control
into and out of the FREE RUN position, the Trigger circuit
is probably causing the trouble. If the trace cannot be turned
off with the LEVEL control, the Sweep circuit is likely at
fault.
CIRCUIT TROUBLESHOOTING
This portion of the Troubleshooting procedure contains
information for locating a defective stage within a given
circuit. Once the stage at fault is known, the component
or components causing the trouble can be located by tube
and component substitution, voltage and resistance measure­
ments, or by short and continuity checks.
As mentioned previously, tube failure is the most preva­
lent cause of circuit failure. For this reason, the first step
in troubleshooting any circuit is to check for defective tubes,
preferably by direct substitiution. Be sure to return any tubes
found to be good to their original sockets.
If replacement of a defective tube does not correct the
trouble, then check to see that components through which
the tube draws current have not been damaged. Shorted
tubes w ill often overload and damage plate load and cath­
ode resistors. These components can sometimes be located
by a visual inspection of the circuit. If no damaged com­
ponents are apparent, however, it will be necessary to
make measurements or other checks within the circuit to
locate the trouble.
Troubleshooting the Power Supply
Proper operation of every circuit in the Type 503 Oscillo­
scope depends on proper operation o f the Power Supply.
The voltages must remain within their specified tolerances
for the instrument to maintain its calibration.
No Output Voltage. If the graticule lamps do not oper­
ate when the POWER switch is turned on, check the POWER
switch, the fuse and line voltage. Shorts in
the
primary
and secondary circuits of T601 will cause the fuse to blow.
If the fuse is not blown and line voltage is correct, next
check the primary windings of the power transformer.
If the graticule lamps operate correctly, the primary circuit
of the power transformer (T601) is operating normally and
the trouble lies some where in the secondary circuit of the
oscillator circuit (V620, T620).
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