HP 4262A - Page 197

Section VIII Model 4262A
Figure 8-12
f. Tum instrument off and on (press LINE button) to reset digital control circuit and to
return test program to its initial address line.
2. Serial numbers 1739J00341 and above.
a. Remove A11, A12, A13 and A14 boards from instrument.
b. Install Signature test board in place of A13 board.
c. Take out the A23 board.
d. Disconnect A23U15 (ROM) from socket J2 and put aside.
e. Connect 24 pin plug of the test board flat cable assembly to socket J2 on A23 board.
f. Reinstall A23 board in its normal position.
g. Tumn insttument off and on (press LINE button) to reset digital control circuit and to
return test program to its initial address line.
Note
When testing ROM’s on A23 board assembly,
install the ROM in socket J2 (labeled 2316A)
on test board. Observe signatures at test
points DO through D7 on the board and
follow troubleshooting procedures. Test
board flat cable may be left connected to A23
board.
SIGNATURE ANALYZER TECHNIQUE.
An
active
digital
hand-held
logic
tracer
coupled
with
an
active
pod
(with
four
miniature
clip
connection
leads)
is
sufficient
for
detecting
the
test
signal
and
for
development
of
the
signature
on
the
Signature
Analyzer
display.
The
active
probe
has
access
to
the
desired
node
in
the
circuit
being
tested
and
transfers
this
input
data
to
the
analyzer.
The
four
input
leads
of
the
test
cable
active
pod,
connect
the
gate
signals
—
START,
STOP,
and
CLOCK
—
from
the
instrument
being
tested
to
the
analyzer.
The
remaining
lead
is
connected
to
instrument
GND.
The
START
signal
is
an
open
“window’’
(measurement
gate)
signal
which
causes
the
signature
analyzer
to
prepare
for
receiving
data
via
the
active
probe.
The
STOP
signal
causes
the
window
to
close.
The
CLOCK
is
taken
from
the
time
base
of
the
instrument
and
permits
receiving
input
data
and
gate
signals
in
synchronization.
Polarity
of
the
gate
signal
active
(enable)
edges
(positive
or
negative)
can
be
selected
by
the
front
panel
controls
of
the
signature
analyzer.
Probing
points
and
connection
locations
of
START,
STOP
and
CLOCK
leads
are
designated
on
the
troubleshooting
flow
diagrams.
Note
Use an -hp- Model 547A Current Tracer to
trace a ‘‘stuck’ node current.
Figure 8-12. Signature Analysis Guide (sheet 2 of 3).
824