Sweep Amplifier - Tektronix 511 Instruction Manual

supplies is abnormally high or low, the load
current for that section may be measured to
determine whether the defect lies within the
power supply or the external circuits. See the
schematic diagram for values. If the power sup­
ply is at fault, the rectifier output voltage should
be checked. Normal rectifier output would then
indicate malfunctioning of the regulator circuit.
See Section 3 for a description of the voltage
regulator circuits. A regulator performance test
is outlined in the Inspection instructions of this
section. A check of the grid-cathode bias of the
series regulator tube will serve to further isolate
the trouble within the regulator circuit itself.
Average bias potentials (S/N455 and up) are:
Line Voltage
V27,6AS7Gbias
105 -14 v
117 -36 v
125 -56 v
Figures 4-5 and 4-6 are oscillograms illus­
trating the amplitude and waveform of the normal
rectifier output ripple. Any unbalance due to de­
fective rectifier tubes or power transformer is
easily observed with an oscilloscope at the
cathodes of V21 and V22-V23.
2. HIGH-VOLTAGE SUPPLY (S/N455 and up).
If normal -1500 and +1500 volt accelerating
potentials are not restored by replacement of
V13, V32, V33, and the HIGH VOLTAGE ADJ.
control, the CRT heater pin plugs and accelerat­
ing anode clip should be removed to ascertain
whether the power supply itself is at fault.
Next check the + 225-volt supply, since the
high voltage output will vary proportionately.
Low output with normal oscillator (VI) grid
and cathode voltages, indicates an open circuit
in the secondary windings of T2, or other por­
tions of the rectifier circuits. Low voltages
at the oscillator grid and cathode would suggest
shorted turns or excessive load on T2, or defec­
tive components in the oscillator primary c ir ­
cuit. Figures 4-7 and 4-8 are oscillograms of
the oscillator waveform.
3. Heater. Since relatively large currents are
present in the heater circuits, it is important
that connections be clean, tight, and joints well
soldered..
P A G E 4 - 4
Sweep Circuits
a spot on the CRT screen can be obtained, but
advancing the SWEEP STABILITY control does
not result in a normal sweep of at least 1 1 cm.
deflection, and at a speed indicated by the SWEEP
RANGE and SWEEP SPEED MULT, controls.
An approximate location of the difficulty can
usually be established by observing the ampli­
tude and waveform of the GATE OUTPUTS,
SWEEP OUTPUT, and the amplified sweep volt­
age at the CRT deflection plates, with another
oscilloscope. Further isolation should be p os­
sible by observing the input and output waveform
of each stage at the tube sockets. A comparison
V25,6AQ5 bias
with figures 4-9 to 4-25, inclusive, will show
whether or not operation is normal. If not,
-8 v
check the tubes, operating voltages and r e sis ­
-16 v
tance values in the suspected circuit.
-22 v
to faulty triggering or to jitter in the signal
being observed, is usually caused by the intro­
duction of a 60-cycle signal due to a defective
tube. This trouble may be located by tube sub­
stitution. Excessive power supply ripple may
also cause jitter.
adjustment controls R42 and C15A) may be
caused by wrong time constants or charging
voltage in the sweep generator, or a change in
gain of the sweep amplifier.
sweep speed is properly adjusted) is due to
faulty operation of the multivibrator.

1. Sweep Amplifier.

amplifier may be indicated by low gain, im ­
proper horizontal positioning, non-linear sweep,
or abnormal CRT deflection plate voltages. To
measure the sweep amplifier gain, set the
SWEEP RANGE switch at EXT. and connect the
CAL. OUTPUT to the EXT. SWEEP INPUT.
With the CAL. VOLTAGE adjusted to 10 volts,
a deflection of approximately 6.5 cm should be
obtained. After trying replacement of V12, V13
and V14, circuit operating voltages and the drop
across each group of neon lamps should be
measured. The potential across five NE2 neon
lamps should be 280 volts +or-30 volts. If
outside this value, make individual lamp meas­
urements, and replace defective units. The
operating potential of new neon lamps may be
T Y P E 5 t t - M A I N T E N A N C E
Trouble in the sweep circuits is indicated when
Instability, or jitter of the sweep, when not due
Abnormal sweep speeds (out of range of the
Short sweep length (less than 11 cm when the
A defect in the sweep