HP 202A Operating And Service Manual page 20

Sect. l V Page 2
4-3 F U N C T I O N G E N E R A T O R
(bi-stable circuit and integrator)
A.
REPAIR ANALYSIS OF FUNCTION GE3lERATOR
m e
voltage, then a simple test should be made to deter-
mine whether the fault is in the integrator o r the
bi-stable circuit. This test
is
a s follows:
1) Connect a high resistance dc voltmeter between
B- and pin 3 of tube V17.
2) Set the R A N a switch to the X . 01 position. Dis-
connect the lead from the center lug of the variable
r e s i s t o r R58. Temporarily connect this lead to
pin 5, V6 (+ 75 Reg. ).
TABLE 4-2. (CONT'D)
3) After this connection is made, the voltage indi-
cated by the voltmeter should slowly climb until it
is over 200 volts.
4-4 S I N E S Y N T H E S I Z E R _ A N D F U N C T I O N
SELECTOR
4) Remove the lead from the
+
75 Reg. supply and
connect it to pin 2, V5 (+225 regulated). The volt- When the trouble has been corrected in the Sine
meter indication should now drop slowly to less than
Synthesizer and Function Selector, the following
140 volts. Disconnect the lead from V5 and return checks should be made to determine if the instru-
it to the original connection on R58.
ment is again functioning correctly.
SYMPTOM
Same symptoms a s
above when frequency
dial is set near low
frequency end.
Triangle not linear.
7
5) If the instrument meets the above voltage r e -
quirements, then the integrator section is functioning
normally and the fault is confined to the bi-stable
circuit. If the instrument does not pass the test,
then the trouble is in the integrator.
CAUSE AND/OR
REMEDY
Try replacement
tubes for V15, V16,
and/or V17.
Replace tubes V15,
V16, V17. Check
-
DC Balance.
After a l l defective p a r t s have been replaced and
the necessary adjustments made, an oscilloscope
should be connected between pin 3, tube V17 and
B- to see
if
a good triangular waveform is obtained
on all ranges.
,
TABLE 4-2.
1) Sine Wave
-
Observe the waveform between pin 2,
V18 and B- with oscillator set to 50 cycles/sec. and
the AMPLITUDE control a t maximum. Set the
FUNCTION switch in the SINE position. The wave-
form should be substantially sinusoidal and approx-
imately 30 volts peak-to-peak. See Figure 3-6B.
SYMPTOM
No output voltage (Power
Supply Section normal,
no triangle voltage be-
tween V17, pin 3 and B-
on any range).
Same symptoms a s above
on one o r more ranges.
Observe the waveform between pin 7, V18 and B-
with the same conditions a s above. The waveform
should be similar to Figure 3-6C and approximately
1 volt peak-to-peak.
CAUSE AND/OR
REMEDY
Replace V1, V2,
V3, Vl5, V16,
o r V17.
If tube
replacement fails
to cure the trouble,
see analysis pro-
cedure following
a
this chart.
Check RANGE
switch contacts,
components, and
connections.
Check C14-C18
for excessive
leakage.
2) Triangular Wave
-
Observe the waveform be-
tween Pin 2, V18 and B- with the oscillator s e t to
50 cycles/sec. and the AMPLITUDE control a t max-
imum Set the FUNCTION switch in the TRIANGULAR
position. The waveform should be triangular and
approximately 30 volts peak-to-peak.
Observe the waveform between pin 7, V18 and B- with
same conditions a s above. The waveform should be
triangular and approximately 1 volt peak-to-peak.
3) Square Wave
-
Observe the waveform between
pin 7, V18 and B- with the oscillator set to 50 cycles1
sec. and the AMPLITUDE control
at
maximum.
Set the FUNCTION switch to the SQUARE position.
The waveform should be square and approximately
30 volts peak-to-peak.
The dc voltage across the OUTPUT terminals should
be adjustable to zero under any operating conditions
by means of R65.