Srq Annunciator (10; Upper Keyboard, Lower Keyboard, Displays (11,12,13 - HP 8340B Manual
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If
the
OVERMOD
annunciator comes on
only
when
a
signal
is
input
to the
FM
jack,
The MODULATION
INDEX (peak
deviation
in
MHz/modulation rate
in
MHz)
of the signal
is
significantly greater than the
specified
maximum
(5).
The OVERMOD LED
(located on the A2 display driver assembly)
is
driven by the A3
display processor,
annunciator latch/driver
circuit.
The
instrument microprocessor detects an error from the circuitry,
outputs the appropriate
bits
to turn
the
LED on, and outputs address 15:R3 to
latch
the data
bits.
SRQ ANNUNCIATOR
(10)
What
is
a
Service Request
(SRQ)
An
SRQ
is
used only when the instrument
is
connected to an external controller
(via
HP-IB). The
controller programs the instrument to send
an
SRQ
under certain conditions. When one of
the
programmed conditions occurs, the HP 8340B/41B
sends out an
SRQ
signal and activates the
SRQ
annunciator.
When
the controller
responds to
the
SRQ
(by doing
a
serial poll command) the
HP 8340B/41B turns
the
SRQ
annunciator
off.
This entire process
takes
a
fraction of
a
second,
so
the
SRQ annunciator stays on only
briefly.
SRQ
Annunciator Stays
On
If
the
SRQ
annunciator goes on and stays on
it
usually indicates
one of the
following conditions:
If
the
HP
8340B/41B
is
Connected to an External controller. The computer
controller
is
not able
to service the
SRQ
interrupt.
The
controller
is
probably stuck
in
a
loop, etc.
This
is
usually not
caused by
an
instrument
fault.
If
the HP 8340B/41B
is
Programmed by an External Controller and then Disconnected.
A
controller can be an external
computer or HP 8756A, 8757A,
or 8510A network analyzer.
The SRQ
annunciator
stays on
if
a
controller has
programmed
the
instrument
to
send
an
SRQ, and
is
subsequently disconnected.
To clear
this
SRQ,
press
[INSTR] [PRESET]
and then cycling the
power
switch to
STANDBY
and
then ON.
The SRQ
(located on the
A2
display driver assembly)
is
driven
by the A3 display processor,
annunciator latch/driver
circuit.
The instrument microprocessor detects
an error from the circuitry,
outputs the
appropriate
bits
to turn the LED on, and outputs address 15:R3 to latch the data
bits.
UPPER KEYBOARD, LOWER KEYBOARD, DISPLAYS
(11,12,13)
Refer to
the front panel
—
rear panel functional group.
A-42
Assembly-Level Service Overall Instrument Troubleshooting
HP 8340B/41B
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