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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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