Model 8901B
Service
8-10.
CONTROLLER
TEST
LEDs AND
TEST
POINTS
Near the top edge
of
the A13 Controller Assembly are located four testpoints and four associated
LED
annunciators labeled
TEST
which are used primarily
for
troubleshooting the instrument. The
LED
annunciators are labeled (from left
to
right)
8,
4,
2,
and
1
and are associated with
test
points A,
B,
C,
and
D
respectively.
The label on the annunciators
is
sometimes used to represent a binary weighting. They function in the
following ways:
1.
At
instrument power-up the
TEST
annunciators light in a certain sequence that indicates proper
functioning of several vital areas of the instrument.
A
failure in any
of
the areas
is
indicated on
the annunciators. For details see
Power-Up
Checks
in
paragraph 8-9.
2.
After power-up, annunciator
1
toggles once for each measurement cycle.
3. After power-up, annunciator
2
toggles once for each keyboard interrupt (that
is,
each time a key
4.
After power-up, annunciator
4
toggles once for each
HP-IB
interrupt.
is pressed).
Grounding of certain of the
TEST
testpoints alters instrument operation in the following ways:
1.
Grounding testpoint
A
is used to alter the measurement halt function of Special Function
43.N.
See
Service
Error
Messages
in paragraph
8-8.
2.
Grounding testpoint
B
causes
some
of
the power-up sequence to be bypassed and thus shortens
the turn-on time of the instrument. The power-up checks are now invalid.
3.
Grounding testpoint
C
initiates the Counter signature analysis troubleshooting routine. See
Service Sheet 23.
4.
Grounding testpoint
D
initiates the Keyboard signature analysis troubleshooting routine. The
signature analyzer's
start
and stop leads are then connected to testpoint
A
and the probe
is
connected
to
testpoint
B.
See Service Sheet 25.
Whenever a testpoint is grounded, the associated annunciator
is
extinguished.
8B-18
Controller Test
LEDs
and Test Points
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