Tektronix 516 series, Instruction Manual

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Maintenance — Type 5 1 6
Check the voltage at the grid (pin 2) of V135A. If the
voltage at this point is in the vicinity of —65 volts or lower
(more negative), the Sweep-Gating Multivibrator is faulty.
In this case, replace V I35 and V I45. If this does not remedy
the trouble, check the rest of the circuit by voltage and
resistance measurements.
If the voltage at the grid of V135A is more positive than
—60 volts, measure the voltage at the grid (pin 2) of V183B.
If the voltage at this point is —70 volts or lower (more
negative), the Hold-Off Circuit is faulty. In this case, replace
V I83, and if this does not remedy the trouble, check the rest
of the circuit by voltage and resistance measurements. (The
cathode of V183B and the grid of V183A should be about
5 to 7 volts more positive than the grid of V183B. However,
there should be a considerably greater voltage differential
between the grid and cathode of V183A.) If the voltage at
the grid of V183B is more positive than about —70 volts,
the Runup Cathode Follower circuit is faulty. If this case,
replace V I61, and if this does not remedy the trouble, check
the rest of the circuit by voltage and resistance measurements.
Nonlinear Sweep.
A nonlinear sweep will be generated
if the current charging the Timing Capacitor does not remain
constant. If the nonlinearity occurs at all sweep rates, a
defective Miller Tube is probably the cause. If the non­
linearity occurs only at certain sweep rates, a leaky timing
Capacitor is probably the cause. A defective C l65 can also
cause the sweep to be nonlinear at the faster sweep rates.
Constant Free-Running Trace. If the free-running trace
cannot be turned off with the STABILITY control, the Sweep-
Gating Multivibrator is at fault. The most probable cause
is a change in resistance in either of the grid circuits or in
the cathode circuit.
Insufficient Horizontal Deflection.
If the horizontal trace
starts at the left-hand side of the screen, but does not extend
to the right-hand side, the Hold-Off Circuit is resetting the
Sweep-Gating Multivibrator before the sweep is complete.
If the sweep cannot be adjusted to normal length with the
SWP. LENGTH adjustment, R176, the resistances in the cath­
ode circuit of V I61B should be checked.
Troubleshooting the Horizontal Amplifier
No Spot or Trace. If a spot is visible when the horizontal
deflection plates are externally shorted together, but disap­
pears when the short is removed, the horizontal deflection
system is in a state of unbalance. The procedure for locating
the defective stage in the Horizontal Amplifier is somewhat
the same as that described for the Vertical Amplifier. That
is, the shorting strap should be removed from the deflection
plates, and connected between the grids of the Output Cath­
ode Follower, V364B and V384B. If no spot then appears, the
Output Cathode Follower stage is at fault.
If the spot does appear, however, the shorting strap should
then be moved back to the grids of the Output Amplifier,
V364A and V384A. No spot on the crt when these points
are shorted together indicates trouble in the Output Amplifier
stage. Check for open resistors in the cathode and plate
circuits.
If the spot appears when the grids of the Output Am­
plifier are shorted together, the trouble lies ahead of the
Output Amplifier.
Insufficient or no Horizontal Deflection. If the gain of
the Horizontal Amplifier decreases, the timing will no longer
correspond to the calibrated values indicated by the TIME/
DIV. control.
If the change in gain is only slight, as indicated by im­
proper timing and a slightly decreased horizontal sweep,
the amplifier can usually be recalibrated. However, since
the gain of the Horizontal Amplifier regulates the timing of
the sweep, care must be taken to insure that the gain ad­
justments are accurately made. Refer to the Calibration sec­
tion if it is necessary to adjust the gain of the Horizontal
Amplifier.
If the decrease in gain of the Horizontal Amplifier is more
pronounced, or if there is no horizontal deflection at all,
check for defective components that can affect the gain but
not the dc balance of the circuits. Such components, in ad­
dition to the tubes, would be the R225, (SWP. GAIN ADJ.),
R347, R377, and R259 (MAG. GAIN ADJ.).
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