Adjustments Model 8904A
Adjustment
2
OUTPUTBALANCE
Description
This adjustment minimizes the signal on the low output of the Floating Output Amplifier on the
A3
or A10 Output Assemblies.
If
the instrument has only one Output Assembly (A3), the adjustments
are made only
to
it.
If the instrument has Option 002 with
two
Output Assemblies (A3 and AlO),
adjustments are made to one or both assemblies. Accessing A3 will require extra disassembly.
If
the
instrument has Option 006 (balanced output), adjustments are made on the A3 assembly with the
balance transformer disconnected.
The instrument
is
set to produce a 10 Vpk sine wave
at
100 kHz into the amplifier. The 48
dB
Attenuator following the amplifier is
set
to 48
dB
so
that the amplifier drives a 500 load. The
unbalanced signal
is
monitored by an oscilloscope at the testpoint on the low output. The testpoint
has a resistor in series with
it
to prevent the oscilloscope from unbalancing the amplifier.
Equipment
Oscilloscope
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HP 1740A or Tektronix 2235
Procedure
1.
Remove the instrument’s bottom cover.
2. If the instrument has Option 002 (a second output assembly) and Output
1
(the output from the
A3 Output Assembly)
is
to
be adjusted, move the A10 Output Assembly out of the way. (Refer
to the disassembly procedure in Figure 5-4.)
3.
If the instrument has Option 006 (balanced output), disconnect the coax cable from A3J400
(OUTPUT HIGH) at the front edge of the A3 assembly. In the steps that follows, when a
reference is made to the
OUTPUTS
1
HIGH
connector, make the connection to A3J400 instead.
4. Connect the oscilloscope’s ac coupled, vertical input to A3TP402 or A10TP402 (FLT
LO)
on the
Multifunction Synthesizer. The oscilloscope should have a low-capacitance
1O:l
divider probe.
5. On the Multifunction Synthesizer, press
SHIFT
PRESET.
After the instrument presets, key in
For A3 Output Assembly
fl
(Channel Config.)
NEXT NEXT NEXT
FREQ
100
kHz
AMPTD
40
mV
For A10 Output Assembly
fl
(Channel Config.)
FREQ
100
kHz
AMPTD
40
mV
6. Set the oscilloscope to measure the 100 kHz signal. Adjust A3C425 or A10C425 (HIGH
FREQUENCY BALANCE) for minimum
100
kHz signal on the oscilloscope but less than
50 mVpp (after accounting for the
1O:l
division by the probe). Use a non-metalic tuning tool.
(Refer to the Component Locator, Figure 5-6.)
7.
If
the Multifunction Synthesizer has Option 006, reconnect the coax to A3J400 and perform
Adjustment 3.
5-6
Adjustment
2
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