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Model 204B
Section
V
Paragraphs 5-25 to 5-30
i
Note
Do not exceed 11 milliamperes. A
charge current exceeding 11 milli-
amperes will shorten battery life.
Replace top cover.
5-26. DC BAL ADJUSTMENT,
5-27. When the DC BAL control R15 (rear panel) is
properly adjusted there should be no dc voltage present
at the oscillator output. If dc voltage is present, pro-
ceed
as
follows:
a. Connect a DC voltmeter to oscillator output.
(With the optional Rechargeable Battery Power Supply,
connect DC voltmeter between floating ground and
the junction of L1 and C102.)
b. Set AMPLITUDE to MAX.
c. Adjust DC BAL on rear of instrument for a zero
volt reading. If necessary, change the value of R18
for proper range of R15. If DC BAL will not adjust to
.zero volts, check power supply for proper voltages.
5-28. DISTORTION ADJUSTMENT,
a.
Connect
a
600-ohm loadacross the oscillator
output terminals.
b. Using a n AC voltmeter, measure the gain con-
trol voltage between circuit ground and a r m of poten-
Table 5-3. Troubleshooting Summary
Indication
No output signal; d c voltage
at
output
greater than
k 1
volt (dc voltage
measured at junction of L1 and
C102 on Option 02 Power Supply
with Rechargeable Batteries)
No output on one o r m o r e ranges
tiometer R36. Voltage should be between 90 and 140
mv r m s on a l l ranges. If voltage is high, increase
resistance of R34;
if
low, decrease resistance.
c. Set Model 204B controls as follows:
RANGE
. . . . . . . . . . . . .
XI00
F R E Q . .
. . . . . . . . . .
l O ( 1 k c )
VERNIER.
. . . . . . . . .
centered
AMPLITUDE.
. . . . . . . . .
MAX.
d. Connect distortion analyzer a c r o s s 600-ohm
e. Measure distortion, and adjust R36 for mini-
load on oscillator output terminals.
mum reading. Reading should be less than 1%.
Note
Do not use coaxial cables (use twin lead
only) and disconnect a l l other equipment
from oscillator when making distortion
measurements.
5-30. Frequency calibration adjustments should be
performed, only
i f
necessary, after repairs
are made
to frequency sensitive components.
5-29. FREQUENCY CALIBRATION ADJUSTMENTS.
a.
Connect frequency counter and 600-ohm load to
oscillator output
as
shown in figure 5-1.
No output signal; proper dc voltage
at
output (zero volts)
Output amplitude not correct and/or
distorted
If all ranges a r e affected
If all ranges are NOT affected
Action
Check power-supply voltages (+13 and -13 volts)
Check Q3, Q4, CR2, and CR3 f o r correct dc voltages
Check Q1, Q2, and CR1 for correct dc voltages
Check power-supply voltages (+13 and -13 volts)
Check Wien bridge components
Check Q1 and Q2 for correct voltages
Check peak detector circuit (Q5, CR4, CR5, and CR6)
Check RANGE switch contacts
Check components connected t o Wien bridge position when
(refer
t o schematic diagram)
(refer t o schematic diagram)
RANGE switch
is inoperative position. For example:
If inoperative position is X1, check C2A and C7A.
RANGE switch is in inoperative position.
Check components connected t o peak detector circuit when
Check power-supply voltages (+13 and -13 volts)
Check components in upper and lower legs of Wien bridge
I
for proper value *percent of tolerance
(refer t o table 6-1
for tolerances). For example: When RANGE switch
is in
X1 position, check R24, R4, C2A, RlOA, RlOB, R11, andC7A
Check peak detector circuit (Q5, CR4, CR5, and CR6, forpro-
per operation. Refer towaveforms and voltages in schem-
atic diagram. Be s u r e CR6 breaks down at 7 volts peak.
respectively
Check for incorrect voltages
at
Q3,
Q4,
Q2, and Q1
~~
~~
Check components connected t o peak detector circuit in
affected range
5-5
01369-4
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