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6.4.4 NOISY OR ERRATIC BALANCES.
N o i s y or erratic b a l a n c e s may b e d u e t o s u r f a c e
contamination of t h e wire-wound C G R L and DQ control
r h e o s t a t s . Contamination c a n form if t h e 1650 Imped-
a n c e Bridge is idle for a n extended period and c a n b e
remedied by rotation of t h e controls s e v e r a l times.
6.4.5 MEASUREMENT ERRORS.
Measurement errors a r e due t o faulty bridge-
circuit components, which c a n b e located with t h e
s e r i e s of measurements l i s t e d in T a b l e 6-4.
Four
standard r e s i s t o r s and one standard capacitor a r e
needed for t h e s e measurements.
1. When a n y one measurement is in error, t h e
faulty component is l i s t e d in T a b l e 6-4.
2. When a l l r e s i s t a n c e measurements a r e in
error, R 4 is out of tolerance.
3.
When both c a p a c i t a n c e measurements a r e in
error, C 1 is out of tolerance.
4. When a l l measurements a r e in error, t h e
CGRL r h e o s t a t is in error.
5. When a l l measurements a t either 1 or 1 0 on
the C G R L d i a l a r e in error, t h e C G R L r h e o s t a t is in
error a t either 1 or 10.
6.
When a l l measurements a r e within tolerance,
a l l the fixed components of t h e bridge a r e within tol-
erance, and t h e C G R L r h e o s t a t is correct a t the l and
10 s e t t i n g s ; t h e C G R L r h e o s t a t s t i l l may b e incorrect
between 1 and 10.
6.5 REPAIR NOTES.
6.5.1 BATTERY REPLACEMENT.
T h e 1650-B Impedance Bridge is powered by four
D c e l l s , which will l a s t for over 500 hours' operation
wit11 normal u s e .
T h e instrument c a n operate with
somewhat reduced battery v o l t a g e , but t h e detector
s e n s i t i v i t y w i l l d e c r e a s e , and t h e oscillator l e v e l w i l l
d e c r e a s e and have i n c r e a s e d distortion.
F o r a quick c h e c k of t h e battery, u s e t h e B A T
CHECK position of t h e GENERATOR switch.
If t h e
meter r e a d s low, r e p l a c e the b a t t e r i e s .
T o r e p l a c e t h e battery c e l l s :
a . Unscrew t h e t w o No. 10-32 s c r e w s from e a c h
s i d e of t h e c a s e (Figure 1-4).
b. Remove t h e instrument from t h e c a s e .
c . Remove the old battery c e l l s from t h e black
fiber tube (refer t o instructions on tube).
d . Observe t h e polarity markings on t h e fiber
tube and i n s e r t t h e new battery c e l l s .
e . R e p l a c e t h e tube between t h e c o n t a c t s .
f. R e i n s t a l l the instrument in t h e c a s e .
g. Tighten the four No. 10-32 s c r e w s .
6.5.2 ETCHED CIRCUIT REMOVAL.
F o r a c c e s s t o t h e e t c h e d circuit shown in Figure
6-2, remove t h e two s c r e w s holding t h e t o p of t h e board
in p l a c e and loosen t h e two s c r e w s a t t h e bottom of the
board one turn. T i l t the board out a s i n Figure 6-2.
(HI
ETCHED
CIRCUIT-
ASSEMBLY
(FIGURE 6-3
ORTHONULL
I
~ 1 0 2
\
OSCILLATOR
ADJUSTMENT
MECHANISM
DETECTOR AMPLIFIER
O R T H O N U L L @
CABLE
-
JIOI
Figure
6
-
2.
Interior
v i e w of
1650-8
Bridge.
SERVICE AND MAINTENANCE 6-5
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