HP 202A Operating And Service Manual page 24

Sect. I ' Page 6
6) Set the AMPLlTUDE control to minimum (max- 15) Switch the FUNCTION selector to TRIANGULAR
imum CCW) and move the voltmeter leads to the
and note the voltmeter indication (0.5 on 0-1 scale is
red OUTPUT terminals. "0 volts1'). Adjust R49 to reduce the dc voltage to
one-half of its initial value, then adjust R51 to remove
7) Adjust R65, located behind a hole in the panel
the remaining dc voltage. The voltmeter should now
near the OUTPUT terminals, for an indication of indicate "0 volts1'.
"0 volts".
8) Set R119, located near V1 and T2, to the middle 16) Set the FUNCTION selector to SINE and adjust
of its range. R118 for a voltmeter indication of "0 volts".
9) Disconnect the voltmeter and connect equipment a s
shown in Figure 4-1.
10) Set the FREQUENCY dial to 10, the RANGE
switch to X10 (100 cps), FUNCTION selector to
SINE, and the AMPLITUDE control f o r an output
of approximately 10 volts rms.
U) Adjust R49 and R51 to eliminate the points o r
spikes a t the ends of the Oscilloscope pattern. Ad-
justment of these controls will shift the output fre-
quenc y, you should follow the frequency shift with the
Distortion Analyzer. Adjust the Distortion Analyzer
sensitivity a s necessary to obtain a useful pattern
on the Oscilloscope.
17) Verify the distortion in the output sine wave a t
100 cps, first on the X10 RANGE with the FRE-
QUENCY dial a t 10, then on the XlOO RANGE with
the FREQUENCY dial
at
1. I£ the distortion indi-
cations a r e not approximately identical, careful
adjustment of R119 will lower the 100 cps distortion
on the XlOO RANGE.
18) Connect the voltmeter COMMON lead to the
common junction of AMPLITUDE controls R93A
and R93B (violet wire). Connect the DC volts probe
to the green wire on the opposite end of R93B.
12) Adjust R60 for minimum distortion
as
indicated
on the Distortion Analyzer. Repeat steps 11 and 12
19) Set the FUNCT ION selector to SQUARE and
until the distortion measured is at least 40 db below the RANGE switch to X10. Adjust R22 for
a
volt-
the output voltage (1%).
meter indication of "0 volts1'.
13) Connect the voltmeter COMMON lead to the
common junction of AMPLlTUDE controls R93A and
20) Any dc between the red OUTPUT terminals with
R93B (violet wire).
the AMPLITUDE control
at
minimum may be elim-
inated by adjusting R65 (behind the hole in the panel).
14) Connect the DC volts probe to the opposite end of This voltage should vary l e s s than
kO.
5 volts when
R93B. This is a
green wire connected to the AM-
the AMPLITUDE control is rotated through
its
full
PLITUDE control. range.
r
\
f
1
r
\
,
1
-hp-
MODEL 2 0 2 A
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MODEL 3 3 0
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MODEL 120 OR 130
LOW FREQUENCY DISTORTION OSCILLOSCOPE
FUNCTION GENERATOR ANALYZER
HORIZ.@
B D - S - 3 8
Figure 4-1. Minimum Distortion and Frequency Adjustment hstrumentation