HP 8340B Manual page 112

7.
Adjust A30C4
for -8V
at TP1.
IF TP1
was
off by more than ±3
volts and
A30C4
is able to
bring it
back to
-8V,
it
is
likely
that the
100
MHz VCXO
is drifting and
A30
should be replaced.
If
TP1 Is still
not —8V, proceed with step
8.
If
TP1
is
now -8V,
proceed
with
step
13.
NOTE:
When making frequency measurements in
steps 8 through
11,
connect the
FREQ STD OUT
from the frequency
counter to the DUT's EXT FREQUENCY STANDARD
input.
If
the instruments are
not connected
in this
way,
a
frequency measurement error may occur. This error
is
caused by the
different
10
MHz
references used by the DUT and the frequency counter.
8.
Connect
the
frequency counter
to A30J1. Connect
a
DVM
and
a
low voltage power
supply (set to
-0.5V) to
TP1 (you are applying
a
voltage between
-0.5V
to
-8V to TP1).
9.
Slowly
change
the power supply voltage
until TP1
measures approximately —8V. While you are
changing the power supply voltage, you should also see the
frequency counter reading approach
100 MHz. If
you are unable to
change the voltage
at TP1, replace the
A30
assembly.
10.
Slowly adjust the power supply for
a
100
MHz frequency counter reading. Slowly increase and
decrease the power supply voltage. You should be able to change the frequency counter reading
above and below 100
MHz.
If you
can change the frequency counter as described, proceed to step
11.
If
you
can't change the frequency counter
reading above and below 100
MHz, remove
the
A30
assembly and
measure
the power supply voltages at the
edge connector.
If
the power supply
voltages are incorrect, troubleshoot the reference loop
—
M/N
loop motherboard and the power
supplies.
If they are correct, replace the A30 assembly.
11.
Turn the
DUT
to
STANDBY and remove the A29 assembly from the instrument.
Install an
extender
board onto the
A29 edge connector. Measure
the resistance between TP1
(TUNE) and A29P1 pin
13.
The
resistance should be
approximately
370S1.
If
the resistance
is correct, proceed with step
12.
If
the resistance
is
incorrect,
remove the A30 assembly and measure the resistance between
A29P1
pin 13 to A30P1 pin 14 and from A29P1 pin 12 to A30P1 pin 12.
In both cases you should
measure approximately Oil.
If
either test
fails,
check the solder connections and replace the wires
connecting the
two edge connectors,
if
necessary.
If both
measure
correctly, replace the
A30
assembly.
12.
Switch the
DUT ON and measure the power
supply
voltages at the A29 edge connector. If
the
power supplies are
correct, replace the A29 assembly. If
the supply voltages are incorrect,
trou¬
bleshoot the reference
—
M/N
motherboard and the
power supplies.
13.
Measure
the frequency and power output from A30J2, A30J3, and A30W1.
If
any of these are at
the incorrect frequency or power
level, proceed to step 14.
If
the output signals from the above
connectors are correct, proceed to
step 15.
14.
Remove the A30 assembly
and install an extender board. Measure the
power
supply voltages at
the A30
edge
connector.
If the supply voltages are correct, replace the A30 assembly. If
the
supply voltages are
incorrect,
troubleshoot the reference
—
M/N motherboard
and the
power
supplies.
15.
Measure
the frequency and
power
output from
A29J2, A29J3, A29J4, and A29J5.
If
any
of these
are at
the incorrect frequency
or power level, proceed
to step
16.
If
the output signals from the
above connectors are correct, proceed to step
17.
16.
Remove the A29 assembly
and install an extender board.
Measure
the power supply voltages at
the A29 edge connector. If the supply voltages are correct, replace the A29 assembly. If
the
supply voltages are incorrect, troubleshoot the reference
—
M/N
motherboard and the power
supplies.
B-10
Reference Loop Assembly-Level Troubleshooting
HP 8340B/41B