HP 8340B Manual page 113

17.
Press [SHIFT] [EXT]. If REF
is
flashing, the DUT
is
incorrectly indicating
a
REP unlock, proceed to
step 18.
If REF
is not flashing,
the reference loop
is operating properly.
18.
Switch the
DUT
to
STANDBY
and install the
A29 assembly
on an
extender board. Remove the A59
digital interface assembly
from the
DUT
and connect the
frequency counter's FREQ STD OUT
to
the DUT's INT
FREQUENCY STANDARD
input. Switch
the DUT ON and measure the voltage at
A29P1
pin 7. The voltage should
be
approximately —0.7V
(note:
if
the voltage is 0V, the
feedthrough capacitor on the
reference
loop
—
M/N
motherboard may be shorted).
If
the voltage
is
incorrect, replace A29.
If
the voltage is
correct proceed
to step
19.
19.
Switch the DUT to STANDBY
and reinstall the
A59
digital interface assembly. Switch the
DUT
on
and measure the voltage
at A29P1
pin
7.
If
the
voltage
is
no longer approximately
—0.7V, remove
the
A59 digital
interface and
check the motherboard connector, A62XA59,
for bent pins.
If
none of
the pins
are
bent, replace A59.
If
the voltage at A31P1 pin
26
is still
approximately —0.7V, trou-
bleshoot the A59 assembly for
a
false unlock indication.
HP 8340B/41B
Reference Loop Assembly-Level Troubleshooting B-ll