Tektronix 585 - Page 58

Maintenance — Type 585
TROUBLESHOOTING THE DELAYED
TRIGGER CIRCUIT
When no delayed trigger is present at the front panel
DEL'D TRIG connector, the Delay Pickoff circuit has probably
failed. However, before attempting to repair the Delay Pick 
off circuit, be sure that the 'A' or 'B' sweep circuits are
working correctly and that a sawtooth voltage is being
presented to the Delay Pickoff system. Also, turn the DELAY 
TIME MULTIPLIER dial away from zero. A properly cali 
brated Delay Pickoff circuit may not deliver any output
pulse during the first minor division of rotation at the zero
end of the helidial.
An excellent aid to calibration of the Delay Pickoff cir 
cuit is a Tektronix Type Z Plug-In Unit used in the test
oscilloscope. The Type Z will permit accurate d c measure 
ment of waveforms several hundred volts from ground. Refer
to the Delay Pickoff diagram for waveform and voltage
measurements.
The first defect to look for is bad tubes, followed by
voltage measurements, and then look for burned or broken
parts.
Check to see that the two grids of the input difference
amplifier can be made to be at the same voltage, either
by sweep sawtooth application or by rotating the DELAY 
TIME MULTIPLIER dial. With the two grids at the same
voltage value, then the plate of V424 should rest near
+ 200 volts.
If the difference amplifier is functioning correctly check
to see if the multivibrator is functioning. It should switch
from conduction of V445B to conduction of V445A when the
grid of V445A rises past about +210 volts. It should switch
back to conduction of V445B when the grid of V445A drops
past about +205 volts.
Another possible trouble, if the multivibrator is function 
ing properly, is the output cathode follower can be held
either in heavy cutoff or heavy conduction by a component
failure in its grid or cathode circuit.
TROUBLESHOOTING THE LOW-VOLTAGE
POWER SUPPLY
Proper operation of every circuit in the Type 585 includ 
ing the plug-in unit, depends on proper operation of the
Low-Voltage Power Supply. The regulated d c voltages must
remain within their specified tolerances for the instrument
and plug-in unit to retain their calibration.
WARNING
Exercise care in checking the power supply. Be 
cause of their high current capabilities and low
impedance, the Low-Voltage supplies can produce
more harmful shocks than the high-voltage supply
in the crt circuit.
Open Primary Circuit (Dead Circuit)
If the pilot lamp and the fan do not come on when the
power is turned on, check the source of power and the
power cord connections. Check the fuse at the rear of
the instrument. If the fuse is blown replace it with one of
the proper value and turn the instrument on again. If the
new fuse blows immediately, check the power transformer
for shorted primary or secondary windings. Also check for
a shorted rectifier. If the new fuse does not blow until the
time-delay relay has activated (a "click ” can be heard),
check for a shorted condition in the regulator circuits and
excess loading on one or more supply.
If the fuse is good, check for an open connection to
the power transformer. If your instrument is wired for 234-
volt operation, check for an open Thermal Cutout Switch,
the resistance of this switch is about 0.1  . (If your instru 
ment is wired for 11 Z-volt operation, the fan will come on
even though the Thermal Cutout Switch is open.)
If both the fan and pilot lamp come on, the power trans 
former is operating normally.
Incorrect Output Voltage
Test points for checking the Low-Voltage Power Supply
including the + 12.6-volt supply, are located on the right
side of the instrument, underneath the Power Supply and
Delay-Line Driver chassis (see Fig. 5-10). The voltage for
each test point (except the +12.6-volt supply) is also silk-
screened on the lip of the chassis adjacent to the ceramic
strip on the top right side in front of the shield covering
the high voltage transformer (see Fig. 5-11). Each regulated
bus is identified by a color-coded wire. The + 12.6-volt bus
is coded black and red on a white wire. The — 150-volt bus
is coded brown, green and brown on a black wire; the
+ 100-volt bus is coded brown, black and brown on a white
wire; the +225-volt bus is coded red, red and brown on
a white wire; the +350-volt bus is coded orange, green
and brown on a white wire; and the +500-volt bus is coded
green, black and brown on a white wire.
If any of the supplies fail to regulate, the first thing to
check is the line voltage. The supplies are designed to regu 
late at a line voltage between 105 and 125 volts with the
design center at 117 volts, or between 210 and 250 volts
with the design center at 234 volts, rms, 50-60 cycle single
phase ac.
If the line voltage is the correct value and waveshape
(peaks are not distorted), the next step is to remove the
plug-in unit and measure the resistance between each regu 
lated bus and ground. The following resistance values are
approximate minimum readings; the actual resistance be 
tween each bus and ground will generally be higher than
the values indicated here.
REGULATED BUS
APPROX. MINIMUM
RESIST. TO GROUND.
No Plug-In Unit.
-150 v 3k
+ 100 v
2.5 k
+ 225 v 12k
+ 350 v
25 k
+500 v
35 k
+ 12.6 v
5-10 
If the resistance values between the regulated buses and
ground check out, check the series regulator tubes. Then
5-12