Function Generator (Bi-Stable Circuit And Integrator); Sine Synthesizer And Function Selector; Output Amplifier - HP 202A Operating And Service Manual

Sect.
I V
Page 1
SECTION I V
MAINTENANCE
4-1 GENERAL 4-2 POWER SUPPLY
All dc voltages are measured with respect to B- and
not with respect to the chassis. The B- points in
the instrument are connected with black hook-up wire.
Most of the following analyzing and adjustment pro-
After power supply parts replacements o r adjust-
cedures require the measurement of dc voltages o r
ments, a final check of regulated voltages should
the observation of waveforms. To obtain accurate be made. See Power Supply Regulator Adjustments
results, use a voltmeter with an input resistance of
in paragraph 4-9.
CAUTION
100 megohms o r more. The @Model 410B Vacuum
Tube Voltmeter is recommended.
Isolate all test equipment from the main chassis o r
gromd Otherwise, both B- and one side of the output
may be connected to the main chassis through the
test equipment. I€ this happens, one cathode resistor
in output stage V20 will be shorted and the tube will
be
severely damaged.
--------------
TABLE 4-1
Whenever p s s i b l e the instrument frequency should
be s e t to approximately 50 cycles/sec. to permit
the use of a capacitor in series with the ac voltmeter
o r oscilloscope to eliminate the dc component.
Interaction between most of the circuits of the Model
202A makes a fairly definite procedure for trouble
shooting necessary. F o r example, a fault in the
oscillator section may easily cause considerable
voltage deviations in the output system. Therefore,
it is more desirable to divide the instrument into
five sections a s follows and consider each in turn.
4-2 Power Supply
4-3 Function Generator
4-4 Sine Synthesizer and Function Selector
4- 5 Output Amplifier
4-6 Sync Out
SYMPTOM
I n s t r k e n t inoperative
(Indicator lamp won't
light, no output volt-
age).
Instrument inoperative
(Indicator lamp lights,
no output voltage).
Instrument inoperative
(normalvoltage atV21).
(Extremely low o r no
voltage between Y5,
pin 5 and B-).
Instrument inoperative
(normal
+
37W reg-
ulated) (+225V reg-
ulated, off voltage).
(+ 7 W regulated, off
voltage)
Instrument inoperative
(No
+
225 regulated
+
75 regulated voltages,
V5 and/or V6 not
ionized).
1
CAUSE AND/OR
REMEDY
Blown fuse, F1.
Measure resistance
from V21 socket
(pins 2 o r 8) to B-.
55,000 ohms o r
more replace V21.
I f
less than 55,000
ohms clear short
circuit in filter o r
regulator circuits
then replace V21.
Defective 6AU5
tubes (V22, V23).
Capacitor C6 short
circuited.
Defective OA2 tube
(V5).
Defective OA3 tube
(V6).
Open circuit in R62,
R84, R85, R91, o r
R92.