HP 8508A - Page 113

i, ge, pi he
Service
8-6
TROUBLESHOOTING
General
Description
The
HP
8508A
mainframe
is
a
dual-channel
IF
processor
that
receives
two
20
kHz
IF
signals
from
the
Input
Module
and
measures
these
to
determine
the
Amplitude
and
Phase
characteristics.
The
results
of
this
measurement
are
presented
on
the
Digital
Display
and
are
available
at
the
HP-IB
programming
Interface.
In
addition,
DC
representations
and
real
time
outputs
of
of
the
Amplitude
and
Phase
values
are
made-available
on
the
instrument
rear
panel.
Instrument
operation
is
under
the
control
of
a
digital
processor
which
also
has
built
in
routines
to
provide
the
data
in
a
number
of
different
formats.
INPUT
MODULE
IF
MEASUREMENT
ASSEMBLY
PULSE
GENERATOR
(F Signal
Figure
8-1.
Simplified
Block
Diagram
of
the
HP
8508A
Vector
Voltmeter
System
Fault
finding
in
the
HP8508A
is
aided
by
the
Self
Test
routine
which
is
run
whenever
the
instrument
power
is
switched
on.
This
routine
checks
the
assemblies
in
the
sequence
shown
in
the
following
table.
The
current
firmware
revision
will
be
shown
in
DISPLAY
2
for
a
few
seconds.
After
this
period,
DISPLAY
1
will
indicate
’tSt’
while
DISPLAY
2
will
show
a
3-digit
series
number
appropriate
to
the
assembly
being
tested.
The
whole
test
routine
takes
approximately
8
seconds
to
complete,
with
the
A5
Processor
Assembly
occupying
about
6
seconds
of
this
time.
Should
an
error
be
detected,
the
routine
will
halt
with
an
error
number
in
Display
2.
E1089
8-3