Racal Instruments 9901 Maintenance Manual page 23

CHECK
FACILITIES
1
MHz
Readout
1
.4
When
the
OPERATE/CHECK
switch
is
set to
CHECK
the
1
MHz
internal
reference
signal
is
fed through the instrument to
provide
an
operational
check
on
'Frequency'
and
'Period'
modes.
Segment
Check
1
.5
With
CHECK
selected the instrument will
display
'all
eights'
when
the
RESET
button
is
pressed, thus
checking
all
segments
in
the display LED's.
DATA OUTPUT
AND
CONTROL
1
.6
The
instrument uses a
parallel-to-serial
data output system.
The data
is
available at a
28-way
connector accessible at
the
rear
panel. Details are
given
in
Table
1
in
the
Technical
Specification.
Accessories are available
to
convert the
data output
to parallel
format. Provision
is
made,
via the
data output connector,
for
the
application of external hold
and
reset control signals to the
counter
in
the
CDI
Chip.
FREQUENCY STANDARD
1.7
A
discrete
component 5
MHz
oscillator
is
fitted in
the basic versions of the
instrument, but at
customer's option
a high
stability
fast-warm-up oscillator
unit
from the Racal range
may
be
fitted.
The
optional unit
should be serviced only
by
Racal Instruments or authorized agent.
An
aperture
in
the rear
panel provides access
for
oscillator calibration.
1
.8
An
external standard,
which
will
automatically over-ride
the internal standard,
can be applied via
the front
panel
'B'
input
socket
for
use
on Frequency and
Period
mode.
A
1
MHz
reference,
derived from the standard
in
use,
is
available via a
rear
panel
BNC
socket.
CARRYING HANDLE
1
.9
The
instrument
is
fitted
with a
combined
carrying
handle and bench
stand.
To
ad|ust the stand, press in the
two handle
bosses
simultaneously while
setting
the stand
to
the desired position.
MAINTENANCE
1.10
The
customer
is
recommended
to
take
advantage of the servicing facilities
offered
by Racal Instruments Ltd.,
and
agents.
9901 Vol
.
2
1-2