Output Amplifier; Sync Out; Tube Replacement - HP 202A Operating And Service Manual

Sect. IV Rage 3
TABLE 4-3.
4 - 5 O U T P U T AMPLIFIER
TABLE 4-4.
SYMPTOMS
Sinewave badly
distorted.
DC component a t OUT-
PUT terminals inde-
pendent of AMPLITUDE
control setting o r varied
by AMPLITUDE control.
. I
CAUSE AND/OR
REMEDY
Maladjustment of
R49, R51, and R6O
o r defective diodes
CR2 through CR13.
Maladjustment of
R65, R54, and R118
o r defective tubes
V4, V18, V19, V20.
See DC Balance
Adjustment.
After adjustment o r 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 r m s 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. I f 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 a t
least 30 volts (10. 6 volts r m s with a sinewave)
when the output is loaded with 4000 ohms o r
higher.
4-6 S Y N C O U T
Specifications call for a negative sync pulse of 10
volts peak with a duration less than 5 microseconds.
The sync pulse occurs a t the sinewave crest and
a t 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
m u s t be tested and if necessary, adjusted to be
within specifications. See paragraph 4-8, Tube
Replacement Chart.