Tektronix 511A-AD, Instruction Manual, Page: 24 / 75

Connect a short wire between the CAL. OUTPUT and
the TRIGGER INPUT binding posts, set the sweep speed
at 10,000 microseconds, the SIGNAL CALIBRATE switch
at .3 v., the CAL. VOLTAGE at 0, the TRIGGER SEL. at
+EXT., the TRIGGER AMPL. fully clockwise, and the
SWEEP STABILITY at a point just below the setting re ­
quired to make the sweep occur. Now advance the CAL.
VOLTAGE control until a stable sweep is obtained. Re­
peat, using the —EXT. trigger setting. If the external trig­
ger sensitivity is normal (.5 volt or less) but internal trig­
gering is inadequate, V17 and associated components
should be checked. See figures 26, 27, and 28 for typical
trigger gain and waveform.
To provide smooth adjustment of the trigger impulse,
a special tapered potentiometer, R6, is employed as the
TRIGGER AMPL. control. It is recommended that this
control be ordered from the factory if replacement is re ­
quired; however a linear potentiometer may be substi ­
tuted if necessary.
Vertical Amplifier.
Defects in the vertical amplifier may be isolated by in ­
troducing a test signal through a series capacitor to
various circuit points, and observing the result on the
511-A's cathode ray tube.
The following precautions should be observed if it be ­
comes necessary to replace circuit components:
1. V1 6, ‘ 6AG7. The heaters of some type 6AG7's intro ­
duce a line frequency signal and
may
cause synchron­
izing difficulty, or vertical deflection of the trace at line
frequency, when the INPUT CHAN. SEL. is in the 2 stages
position. Since 6AG7's exhibit a marked variation of in ­
put capacity, it is desirable to check the adjustment of
C44,
as explained
in
the "Adjust
of Input
Attenuator"
section. If satisfactory waveshape cannot be obtained,
try
another
6AG7.
2. C39, C51. These electrolytic capacitors are em ­
ployed in the low frequency compensating circuits, and
should be replaced if the range of R99 and R116 be­
comes insufficient to properly compensate the amplifier.
It is necessary that the actual capacity be within the
limits specified in the "Parts List" section.
3. R111, R 111. 1, R1 12, R112.1, R126, R126.1,
R127 and
R127.1. These are V 1 8 and V19 plate load resistors. If re ­
placement is necessary, the values must be selected so
that
the
total resistance of each
series of
four
is between
1125 to 1250 ohms. After replacement, it is desirable to
check the high frequency response of the amplifier, and
if necessary, readjust as explained under "Adjustment
of Vertical Amplifier H.F. Response."
4. R93 and R93.2. These are the V 16 plate load resist ­
ors. Replacements should be selected for a total series
value between 1175 and 1240 ohms, and
the
adjustment
of L4 and L5 checked.
5. R107, VERT. AMPL. ATTEN. If this control must be
replaced in the Type 511-AD, it may be necessary to in­
stall a different value Delay Network shunt resistor. See
Section VII. This control has an additional rotation stop
punched in the cover; therefore the cover should be re ­
moved and installed on the new control, unless a re­
placement is ordered from the factory.
6. Wiring Dress. Since the Type 511-A is designed to
observe
high
speed
transients, it
is
important that
the
original low capacity construction in the vertical ampli ­
fier
signal
circuits be maintained. Therefore,
when
re­
placing any electronic components or wires, be sure
that the original positions are maintained. The leads
between the deflection plate access panel and the CRT
socket should be dressed apart and away from other
conductors.
TYPE 511-A, 51 1-AD
SECTION 4, PAGE 4