Model 333A/334A
Section
V
voltage
is
not present, check sensitivity
vernier and check function switch connections.
5-43. AUTOMATIC CONTROL CIRCUIT.
5-44. The automatic control circuit
is
made up of
two
control loops-resistive and reactive-that
are
identical with the exception of the 900 phase lag
cir-
cuit
in
the reactive loop. The following steps
list
a
procedure for checking the resistive loop only; how-
ever, the same general procedure can
be
used to
check the reactive loop.
Refer
to the schematic
dia-
gram
of
Figure
7-5 for circuit voltages and wave-
forms,
as
well
as
the 333A/334A control settings.
5-47. PHOTORESISTOR CHECK
a.
Turn 333A/334A off, and set MODE to
MANUAL and FREQUENCY RANGE to X1K.
b. Disconnect
all
wires
to A6 board except to
pins 6, 7, and 8 (lamp drive voltage connec-
tions).
c. Turn 333A/334A on, and check value of
photoresistors at pins listed in Table 5-9.
Allow a tolerance of
*20%
on values.
Table 5-9. Photoresistor Check
I
PHOTORESISTOR
I
PINS(A6)
I
RESISTANCE
a.
Check waveform
at
A5TP1.
If
proper wave-
form
is
present, proceed to step
b;
if
not go
to step
f.
b. Check waveform at A5TP2.
If
proper wave-
form
is
present, proceed to step c;
it
not go
to step
e.
Measure dc voltage
at
AB-pin 17forapproxi-
mately +16V (manual mode).
Set
FUNCTION
to DISTORTION, and manually null the input
signal.
Set
MODE to AUTOMATIC, turn
BALANCE
COARSE
control fully counter-
clockwise and check
for
approximately e20
Vdc
at
AB-pin 17. Then turn BALANCE
COARSE
control fully
clockwise
and check
for
approximately
+12
Vdc
at
A5-pin 17.
If
proper voltages
are
present, check
photoresistors
as
outlined
in
Paragraph 5-46.
If
proper voltages
are
not
present,
go
to step d.
c.
6
Measure dc voltage
at
A5TP3 for approxi-
mately -0.5 V (manual mode). Set MODE to
AUTOMATIC, turn BALANCE COARSE con-
trol fully counterclockwise and check for
approximately
-1
Vdc
at
A5TP3, then turn
BALANCE COARSE control fully clockwise
and check for
0
Vdc
at
A5TP3.
If
proper
voltages
are
present, check A5Q6.
If
proper
voltages
are
not present, check A5Q5 and
check MODE switch connections.
e.
Check waveform
at
A5-pin 16.
If
proper
waveform
is
present, check A5Q1 through
A5Q4 and associated circuitry.
If
proper
waveform
is
not present, check A2R50.
Check waveform
at
negative side of A5C10.
If proper waveform
is
present, check A5Q7
through A5Q9 and associated circuitry.
If
proper waveform
is
not present, check R6.
f.
5-45. PHOTORESISTOR CHECK AND ADJUSTMENT
(A6V1 thru A6V5).
5-46. The following steps give
a
procedure for
checking, and
if
necessary, adjusting the photoresis-
tors in the Wienbridge balancing circuit. Paragraph 5-48
tells
how to check the resistance of each individual
photoresistor.
If
a
photoresistor
is
not within toler-
ance, adjust the resistance
of
it
according to the step8
in
Paragraph 5-48.
11
1
::
io
1
j
1,
10 15 kS2
3, 4 150 kS2
v5 5, 10 150
kS2
If
any resistance value
is
out
of
tolerance,
refer to Paragraph 5-48.
If
all
values
are
within tolerance, reconnect
wires
to A6
board. (See Figure 7-1
for
wire color code
diagram
of
A6 board).
d.
5- 48. PHOTORESISTOR ADJUSTMENT
v
NOTE
If
the photoresistors
are
adjusted,
perform the Bridge Balance Adjust-
ment, Paragraph 5-30.
a.
b.
C.
d.
e.
f.
Turn 333A/334A off, and
set
MODE to
MAN-
UAL and FFtEQUENCY to
XlK.
Disconnect all wires to A6 board except to
pins 6, 7, and 8 (lamp drive voltage
connections).
Remove A6 board mounting screw (access to
mounting screw
is
through hole in
A3
board).
Remove screw which holds plastic cover to
A6 board, and remove plastic cover.
Adjust resistance of photoresistors
by
re-
positioning individual photoresistor around
light source.
If
resistance
is
low,
move
photoresistor away from light source;
if
resistance
is
high, move photoresistor closer
to light source. After repositioning
a
photo-
resistor, replace plastic cover on A6 boards
so that photoresistor
is
not affected by
out
side light. Then measure resistance
of
photore sistor .
If
an
individual photoresistor cannot
be
ad-
justed within tolerance, replace the photo-
resistor.
After adjusting photoresistors, replace screw
securing plastic cover to
A6
board
and replace
A6 mounting screw. Reconnect
wires
to A6
board (See Figure 7-1 for wire color
code
diagram of A6 board).
5-15
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