HP 654A - 5-65. Level Flatness Adjustments; 5-66. 75 UNBAL Flatness

Section V
Model 654A
4) Repeat step 5-55d as often as necessary until
tolerances are met at both 5 and 10 settings of
the FREQUENCY dial. If S2C6 does not have
sufficient range, change the value of S2C7* in
accordance with Table 5-4 ; similarly, for S2C12
change S2C15*.
e. Set the 654A FREQUENCY dial to 1; the counter
should indicate 1000 ± 20 kHz and A2TP2 voltage
should be between - 0.3 V to - 0.4 V; if frequency
or A2TP2 voltage is not within tolerance, pad
range resistors S2R8* and S2R16* simultaneously
in accordance with Table 5-4.
NOTE
It may be necessary to set the frequency
high at 10 on dial in order for the dial to
track.
f. Set the dial to 10 and repeat steps c and d if
necessary.
g. Check frequency tracking of the dial at the
settings given in Table 5-2 for the X 1M range; if
any of these are not within tolerance, repeat steps
c through g of this paragraph. A2TP2 voltage
should be within - 0.25 to - 0.42 volts over the
entire range.
5-56. X100K RANGE ADJUSTMENTS.
a. Connect the equipment as shown in Figure 5-15.
Set the 654A controls as in Paragraph 5-50b
except set FREQUENCY RANGE to X100K and
FREQUENCY dial to 1.
b. Note the A2TP2 voltage which should be between
- 0.3 V to - 0.4 V; set the FREQUENCY dial to 10
and adjust S2C4 and S2C10 for a counter indica-
tion of 1 MHz ± 20 kHz and an A2TP2 voltage as
noted above. If S2C4 does not have sufficient
range, change the value of S2C5* in accordance
with Table 5-4; similarly, for S2C10, change the
value of S2C11*.
c. Check the FREQUENCY dial tracking using the
settings and tolerances given in Table 5-2 for the
X100K range. If not in tolerance, repeat step b but
set the frequency ( with dial at 10) towards the
lower or upper limit of the tolerance given in
Table 5-2 so that the dial will track as required.
5-57. OUTPUT WAVEFORM CHECK.
a. Connect the 654A 50 ohm output to the
oscilloscope; terminate the cable from the 654A
with a 50 ohm feedthru.
b. Set the 654A controls as follows:
AMPLITUDE extreme counter- clockwise
OUTPUT LEVEL dBm extreme
clockwise
IMPEDANCE 50 UNBAL
c. Check the 654A output waveform for spurious
oscillations or visible distortion; check all
frequencies by sweeping the FREQUENCY dial
across the whole range at each FREQUENCY
RANGE setting. If distortion or spurious
oscillations occur, eliminate by changing the value
of A2C8*.
NOTE
If A2C8* is changed it may be necessary
to recalibrate the X1M and X100K
ranges.
5-58. METER TRACKING AND AMPLITUDE CONTROL
ADJUSTMENTS.
5-59. METER RANGE ADJUSTMENT.
a. Set the 654A controls as follows:
FREQUENCY dial 1
FREQUENCY RANGE X1K
OUTPUT LEVEL dBm + 10,0
IMPEDANCE 50 UNBAL
b. Adjust A3R18 ( Meter Cal) to its extreme
clockwise position.
c. Adjust A3R7 ( Meter Offset Cal) so that the
AMPLITUDE control has sufficient range to
exceed the maximum meter deflection at both
ends of the meter scale.
d. Adjust the 654A AMPLITUDE control for a meter
indication of - 1dBm.
e. Connect the equipment shown in Figure 5-16 and
set the external attenuator for OdB attenuation.
f. Adjust the reference supply for null indication on
the dc null voltmeter ( which should be set to
either the 30uV or 100uV range).
g. Set the external attenuator to - 2dB position and
adjust the 654A AMPLITUDE control to return
the dc null voltmeter indication to null.
h. Adjust A3R18 ( Meter Cal) until the 654A meter
indicates + 1dBm.
5-16