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rms between the HIGH terminal and the c a s e of the
bridge. T h i s puts 30 p V rms into the amplifier, which
should c a u s e a t l e a s t a 2-division meter deflection.
e . Turn t o AC INTERNAL 1 kHz and adjust t h e
OSC L E V E L for 0.5 V rms between the HIGH terminal
and the c a s e of the bridge. T h i s puts 5 ,LLV rms into
the amplifier and should c a u s e a t l e a s t a 1-division
deflection.
If i t doesn't, it c a n be that the oscillator
frequency and the peak amplifierresponse don't coincide.
If the detector amplifier o s c i l l a t e s in the AC
INTERNAL 1 kHz position, it could be that the feed-
back i s too great. R155 should be increased t o perhaps
20 k n . T h e green and brown amplifier output wires a t
S103 should be routed away from the amplifier input
wire, which i s the shielded c a b l e with the brown p l a s t i c
band. If they are too c l o s e , the amplifier may oscillate.
If the amplifier is inoperative, a stage-by-stage voltage
check should be made (Table 6-8).
6.5.8
INTERNAL GENERATOR.
Use the s e t u p of Figure 6-3 and measure the rms
voltage between the HIGH terminal and the c a s e . With
the oscillator level full cw it should be within the
range of 0.9 V t o 1.1 V.
6.6.9
F INAL ACCURACY/OPERATlONAL CHECK.
The measurements given in Table 6-1 are de-
signed to:
1. Check the accuracy of the ratio r e s i s t o r s ,
R 4
to
R14.
2. Check the continuity and proper operation of
the CGRL PARAMETER, function, and CGRL MULTI-
PLIER switches and the EXT GEN and UNKNOWN
terminals.
3. Recheck the accuracy of the DQ and CGRL
dia 1s.
Trouble-shooting notes:
1. Since the DQ and CGRL d i a l s have been
checked, incorrect readings on any range will ordinarily
be c a u s e d by the ratio resistor, R A , for that range
(R4 t o R14).
2.
If R DC INTERNAL
6
V readings are incor-
rect, be sure the NULL meter is zeroed.
6.7 KNOB REMOVAL.
If i t should be necessary to remove the knob on
a front-panel control, either t o repIace one that h a s
been damaged or to replace the a s s o c i a t e d control,
proceed a s follows:
a. Grasp the knob firmly with the fingers, c l o s e
into the panel (or the indicator d i a l , if applicable), and
pull the knob straight away from the panel.
CAUTION
Do
not
pull
on
the dial
to
remove
a
dial/knob
assembly.
Always remove
the knob first. To avoid damage
t o
the
knob and other parts of the
control,
do
not pry the knob
loose
with
a
screw-
driver
or similar
flat
tool,
and do
not
attempt
to
twist the knob from the dial.
b. Observe the position of the setscrew in the
bushing, with respect t o any panel markings (or a t the
full ccw position of a continuous control).
c. R e l e a s e the setscrew and pull the bushing
off the shaft. Use a No. 10 Allen wrench for the CGRL
PARAMETER and MULTIPLIER bushings and a No.
for the DQ bushings.
d. Remove and retain the black nylon thrust
washer, behind the dial/knob assembly, a s appropriate.
NOTE
T o separate the bushing from the knob,
if for any reason they should be com-
bined off the instrument, drive a machine
t a p a turn or two into t h e bushing for a
sufficient grip for e a s y separation.
6.8 KNOB INSTALLATION.
T o install a knob assembly on the control shaft:
a. P l a c e the black nylon thrust washer over the
t h e control shaft, if appropriate.
b. Mount the bushing on the shaft, using a small
slotted piece of wrapping paper a s a shim for adequate
panel clearance.
c. Orient the s e t s c r e w on the bushing with
respect t o the panel-marking index and lock the s e t -
screw with the appropriate hex-socket key wrench
(paragraph 6 . 7 ~ ) .
NOTE
Make sure that the end of the shaft d o e s
not protrude through the bushing or the
knob won't bottom properly.
d. P l a c e the knob on the bushing with the reten-
tion spring opposite the setscrew.
e. P u s h the knob in until it bottoms and pull it
slightly t o check that the retention spring i s seated in
the groove in the bushing.
NOTE
If the retention
spring in the knob
comes loose, reinstall it in the interior
notch that h a s the thin s l i t in the s i d e
wall.
It will not mount in the other
notch.
SERVICE AND MAINTENANCE 6-8
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