HP 202A Operating And Service Manual
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Sect.
IV
Rage 3
TABLE 4-3.
4-5 OUTPUT AMPLIFIER
TABLE 4-4.
SYMPTOMS
Sinewave badly
distorted.
DC component at OUT-
PUT terminals inde-
pendent of AMPLITUDE
control setting or varied
by AMPLITUDE control.
.I
CAUSE AND/OR
REMEDY
Maladjustment of
R49, R51, and
R6O
or defective diodes
CR2 through
CR13.
Maladjustment of
R65, R54, and R118
or defective tubes
V4, V18,
V19, V20.
See DC Balance
Adjustment.
After adjustment or tube replacement, the amplifier
should meet the following specifications:
SYMPTOMS
Increased distortion
when amplifier
is
loaded with 4000 ohms.
DC voltage component
exists across the OUT-
PUT terminals.
Distortion increases
appreciably with re-
duced AMPLITUDE
control setting.
Failure to deliver 10
volts rms
sinewave
output.
Hum in output voltage.
---
The output voltage should not drop more than
2%
when a 4000 ohm load
is
connected to the
output.
>
CAUSE AND/OR
REMEDY
Replace
Vl8, Vl9,
V20.
If
distortion
remains, turn off
the power and mea-
sure resistance be-
tween internal
chassis and main
chassis. See para-
graph 4-9.
See paragraph 4-4.
Replace variable
resistor
R93A,
R9 3B.
Adjust regulated
&
voltage. See para-
graph 4-9.
Replace
Vl8, Vl9,
v20.
Excessive hum from
power
supply See
paragraph 4-9.
---
The distortion should remain within specifi-
cations when the output
is
loaded with 4000 ohms
or higher.
---
The peak-to-peak output voltage should be at
least 30 volts (10. 6 volts rms with a sinewave)
when the output
is
loaded with 4000 ohms or
higher.
4-6
SYNC OUT
Specifications call for a negative sync pulse of 10
volts peak with a duration less than 5 microseconds.
The sync pulse occurs at the
sinewave crest and
at corresponding positions on other waveforms.
TABLE 4-5.
4-7
TUBE REPLACEMENT
SYMPTOMS
No sync pulse (Check
for negative pulse
with oscilloscope and
with Mode1 202A set
for highest frequency).
Large overshoot.
,
Any tube with standard JETEC characteristics can
be used for replacement purposes.
CAUSE AND/OR
REMEDY
Replace
Vl7.
Replace CR1.
Whenever a tube
is
replaced, that part of the in-
strument which might be affected
by
the change
must be tested and
if
necessary, adjusted to be
within specifications. See paragraph 4-8, Tube
Replacement Chart.