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SERVICE AND MAINTENANCE
each of the b r a s s brackets on either side of the motor
laminations.
5.4.2 C L E A N I N G T H E AIR F I L T E R .
T o maintain proper cooling efficiency, the air
filter should be cleaned periodically. Local air condi-
tions determine how often t h i s is necessary. T o c l e a n ,
release the air filter from i t s holder,rap gently to remove
e x c e s s dirt, flush from the dirty side with hot soapy
water, rinse, and let dry. Commercially available prep-
arations t o increase the filtering efficiency may be
applied but are not necessary.
5.5 TROUBLE-SHOOTING NOTES.
5.5.1 G E N E R A L .
If the pulse generator is inoperative, make the
following simple checks before proceeding further:
a . Check the power line voltage and frequency t o
make sure they are a s required by the power supply.
b. Check line cord, f u s e s , and power supply voltage.
If the voltage from pin 3 of V501 t o ground is not
150 volts or if the voltage from pin 2 of V504 i s not
-150 volts, refer to paragraph 5.5.2.
c . See if theprepulse i s present a t the SYNC binding
posts. If this pulse i s present and the main pulse i s
defective,refer to paragraph 5.5.2. If the prepulse is
present and there i s no main pulse, refer toparagraph
5.5.3.
I f
neither prepulse nor main pulse is present,
refer t o paragraph 5.5.4. If prepulse is absent and
the main pulse i s present, refer to paragraph 5.5.7.
5.5.2 I N O P E R A T I V E POWER S U P P L Y .
Incorrect voltage. If
the positive supply voltage
at pin 3 of V501 i s regulated but not + I 5 0 volts with
respect t o ground, first s e e if the negative supply volt-
age a t pin 4 of V504 i s -150 volts. If this voltage i s
regulated but not correct, adjust R512 s o that an a c -
curate voltmeter indicates + I 5 0 volts from pin 3 of
V501 to ground. If the positive supply voltage adjust-
ment drifts, but the negative supply voltage d o e s not,
replace either R504, R506, or R505. If the negative
supply voltage adjustment drifts, replace R511, R513,
R510, R512, or V504.
If the voltage drops only a t full load, replace
V501, and check the voltage at pins 2 and 5 of V501.
If either of t h e s e v o l t a g e s is l e s s than 210 volts, check
the corresponding capacitors and diodes.
Unregulated voltage.
The most probable c a u s e of
this trouble i s a defectivetube. Remove V502 and V503
test them, and replace any defective tube. Measure the
voltage a t pin 2 of V503 with respect to ground. If t h i s
i s not within 5% of
-66
volts, regardless of the output
load, replace V504. Measure the r e s i s t a n c e s to ground
from pin 2, pin 3, pin 5 , and pin
6
of V501 and compare
the results with the values in Table 5-1. Replace any
defective resistors or capacitors thus found.
N o output supply
voltage.
Check V501. Measure
the regulator input voltage a c r o s s C501 and C502.
If
either of t h e s e voltages is zero, check for a shorted
rectifier diode, C501, C502, and a blown fuse in the
primary of T501. If the input voltage is normal, check
V502 and V503 for a n internal short. Check V504 for a
short. Measure the voltages a t key points with a vacuum
tube voltmeter, comparing them with those given in
Table 5-1.
Incorrect
heater
voltage.
If the d c voltage a t pin 4
of V103, V105, or VlO6 or pin 3 of V503 i s not within
10% of -70 volts, check for a cathode-heater short in
one of those tubes. Check the resistance to ground from
pin 2 of V504 against the value in Table 5-1. Replace
any defective resistors. Check for a short in C504 or
c 5 0 5 .
5.5.3 D E F E C T I V E MAIN PULSE.
Overshoot.
Under normal conditions, with a high
impedance load, overshoot i s not possible on any tran-
sition. Therefore, check the oscilloscope for overshoot
first. I f overshoot occurs with a low-impedance termi-
nated system, check the system for proper grounding
and make sure that a l l wiring is a s short a s possible.
Note that some overshoot may be present on negative
pulse transitions a s shown in Figure 3.6.
Large imbalance in pulse amplitudes
or
slowly
falling negative-going edge of positive pulse.
T h e s e
defects c a n be caused by weakening of one of the out-
put tubes.
Output pulse occasionally fails, and
starts
only
when RANGE switch setting
i s
changed.
There are two
possible c a u s e s of t h i s difficulty: (1) The ionization
voltage of V107 h a s drifted sufficiently s o that the
automatic restarting circuit no longer functions, or (2)
a tube h a s developed heater-to-cathode leakage. F i r s t
check the voltage from the negative s i d e of V107 t o
ground, using a n electronic voltmeter of a t l e a s t 100
megohms input impedance. The proper voltage i s -65
t 5 volts behind 5 megohms. I F t h i s voltage i s correct,
the trouble is a defectiveV107, and a newNE-96 should
be installed.
If
the voltage measured i s not correct,
check a l l tubes for heater-to-cathode leakage.
Pulse-duration
errors.
An error indication on only,
one setting of the RANGE switch i s an indication that
a time-determining component for that range h a s drifted
or failed.
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