Tektronix 585 - Page 57

Maintenance — Type 585
manner in which it is held may be determined by measur 
ing the voltage at the SAWTOOTH A binding post. If
the Miller circuit is held at the high end of the sawtooth
the voltage at the front-panel binding post may measure
about +300 volts; if held at the low end, the voltage at
this point will measure anywhere between ground and — 20
volts, depending on the cause. If it rests at — 20 volts, the
frouble probably is non-conduction of V152A, and it should
be replaced. It can also mean that R151 is open.
If the Miller circuit is held at the high voltage end of the
sawtooth, replace V 1 52 as it can mean both heaters are
open. Or replace the Miller tube V 1 61 as its heaters can
be open or its cathode can have low emission and give
the same effect. Usually if V 1 61 is not conducting, B 1 67 will
be glowing brightly.
In the event the front panel SAWTOOTH A jack voltage
rests at +350, there is probably a grid to plate short within
V 1 73; replace it. When this occurs, B 1 67 glows brightly at
the electrode attached to pin 6 of VI 61. If this reverse
conduction condition is permitted to continue for longer
than about 15 minutes it may be necessary to replace B167
with a new neon glow tube. The reason for this is that
Bl 67 may be unstable thereafter.
If the heater of V 1 73 is open, both neon glow tubes will
be glowing brightly and there will be no sweep.
If all tubes have been checked, then check for open plate
and cathode resistors in the Sweep Gating Multivibrator
circuit, the Hold-Off circuit and the Runup CF circuit. Also
check that the STABILITY control can vary the voltage at the
grid of V135A.
Nonlinear Sweep
A nonlinear sweep voltage will be generated if the cur 
rent charging the Timing Capacitor C 1 60 does not remain
constant. If the nonlinearity occurs at all sweep rates a defec 
tive Miller tube is the probable cause. If the nonlinearity
occurs only at certain sweep rates a leaky Timing Capacitor
is the probable cause but the Miller tube should not be
overlooked. A defective bootstrap capacitor C 1 65 can
cause the sweep to be nonlinear at the faster sweep rates.
If the sweep appears linear in all but the 1 and 2 SEC/CM
rates, or if the spot moves to a point near the center of the
crt and stops there, there is likely heater-cathode leakage
in V 1 52B and it should be replaced.
Insufficient Horizontal Deflection
If the horizontal trace starts at the left side of the grati 
cule, but retraces before reaching the right side, the Hold-
Off circuit is causing V135A to revert the sweep too soon.
If the trace cannot be expanded to the full width of the
graticule with the SWP. LENGTH control R176, check the re 
sistance values in the cathode circuit of V173.
TROUBLESHOOTING THE HORIZONTAL
AMPLIFIER
No Spot or Trace Visible on CRT
To determine whether the Horizontal Amplifier is in a
state of d c unbalance, short the horizontal deflection plates
together at the neck pins of the crt in the manner explained
for troubleshooting the Vertical Amplifier. The horizontal
deflection plates are marked RED (LEFT) and GREEN (RIGHT).
The INTENSITY control should be set to mid-range. If a spot
appears when the horizontal deflection plates are shorted
together (it may be necessary to adjust the VERTICAL POSI 
TION control), the trouble lies in the Horizontal Amplifier.
CAUTION
Do not permit the spot to remain on the crt at
this setting of the INTENSITY control. Either re 
duce the intensity until the spot is just visible, or
remove the short from the horizontal deflection
plates.
The procedure for troubleshooting the Horizontal Ampli 
fier is similar to that explained for troubleshooting the
Vertical Amplifier for unbalance. The shorting strap can be
moved from deflection plates back toward the Input Ampli 
fier stage, until a point is reached where the trace does
not appear. When the stage at fault is determined, check
for defective tubes and components associated with that
stage.
Insufficient or No Horizontal Deflection
If the gain of the Horizontal Amplifier decreases from
normal, the trace will not extend from the left to the right
side of the graticule. In addition, the timing will no longer
correspond to the calibrated value indicated by the TIME/CM
switch. (This is to distinguish insufficient sweep caused by
trouble in the Horizontal Amplifier from that caused by a
trouble in the Time-Base Generator, e.g., an improper ad 
justment of the SWP. LENGTH control. In the latter case
the trace will be shortened but the timing will not be af 
fected.)
If the change in gain is slight, as indicated by improper
timing and a slightly decreased sweep, the amplifier can
usually be recalibrated. Since the gain of the Horizontal
Amplifier affects the timing of the sweep, care must be
taken to insure that the gain adjustments are accurately
made. Be sure to refer to the Calibration Procedure 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 sweep at all (in which case only
a spot will be visible on the horizontal axis), check for de 
fective components which can affect the gain but not the
d c balance. In addition to the tubes, such components are
the common cathode resistors and controls.
TROUBLESHOOTING TIME-BASE B
TRIGGER AND SWEEP CIRCUITS
By following the circuit description of various Time-Base A
and Time-Base B circuits, you will note a great similarity
in most. Therefore it is felt that the preceding trouble 
shooting procedures for Time-Base A trigger and sweep
circuits is adequate for a guide when problems exist with
the Time-Base B system. The exception of course is that
the HORIZONTAL DISPLAY switch must be in the B position.
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