Model
8903B
Service
CONTROLLER TEST LEDs AND TEST POINTS
8-28. CONTROLLER TEST LEDs AND TEST POINTS
Near the top edge of the
A8
Controller/Counter Assembly are located four
test
points 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
way:
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,
paragraph 8-27.
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 is pressed).
4. After power-up, annunciator
4
toggles once for each
HP-IB
interrupt.
Grounding of certain of the
TEST
test
points alters instrument operation in the following ways:
1. Grounding
test
point C on power-up initiates the Counter, Latch, and Controller
1/0
signature analysis
troubleshooting routines. See Service Sheet 14.
2.
Grounding
test
point
D
on
power-up initiates the Keyboard signature analysis troubleshooting routine.
The signature analyzer’s
start
and stop leads are then connected
to
test
point
A
and the probe leads are
then connected
to
test
point
B.
See Service Sheet
17.
Whenever a
test
point
is
grounded, the associated annunciator
is
extinguished.
rev.2OJUN8
7
8-19
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