Oven Annunciator (5 - HP 8340B Manual

Fan Does Not Turn Off
When the instrument is in
the STANDBY mode, the fan should not run.
If it is, the fan relay (K1) may be
stuck,
or the
+22V
supply has failed.
The
fan relay solenoid
is
energized when the instrument
is in
the
STANDBY mode,
turning the fan
off. If the
power
to the relay solenoid
fails
(+22V
supply), the
solenoid
de-energizes,
turning the fan on.
INSTRUMENT CHECK LEDS REMAIN ON (4)
Instrument check
LEDs I
and II, located on the front panel adjacent to the
[INSTR PRESET]
key,
indicate the results of self test. After switching the
power on or pressing
[INSTR PRESET], the
following occur:
1.
Both LEDs turn on.
2.
LED I
turns off when the instrument processor determines
it is
operational, and has verified
memory and the peripheral interface timer.
3.
LED
II
goes
off
when
the
processor determines that the I/O address
bus,
I/O
data bus, and the
marker ram are operating.
If
no failure occurs during self test, both INSTR
CHECK
LEDs go off
after about
1
second.
If
either
remain on, the instrument requires service. Refer to the controller section functional group for
trou¬
bleshooting information.
NOTE:
Instrument self test
does
not detect all instrument failures.
If
you suspect
a
problem and self
test passes, perform the service diagnostic routine, SHIFT M4
(see
FRONT PANEL DIAGNOSTICS).
OVEN ANNUNCIATOR
(5)
The front panel OVEN
light indicates the status of the internal frequency standard. When the OVEN
annunciator
is
on,
the frequency is
more than 100 Hz from 10
MHz. The
A51
assembly
10
MHz
reference
oscillator has an internal
circuit that monitors the internal oven temperature. When the oven
temperature
is too low, the
HOVC
line
is high (greater than
+15V). When
the oven temperature
reaches the desired point (the frequency is
within 100
Hz of
10 MHz), HOVC
goes
low (less than
+15V). HOVC
is
sent to the
A59 digital
interface assembly where the microprocessor reads
it
and
determines when to
turn the light on or
off.
The oven LED
is
located on the A2 display driver assembly, and
is
driven
by the A3
display
processor,
annunciator latch/driver.
The
LED
is
turned on by the instrument processor. The
processor outputs
the appropriate
bits on the
data bus, then outputs address
15:RO to latch
the data
bits.
If
the
internal 10
MHz
standard
is used, the
OVEN annunciator
should go out within one-half hour after
the instrument is connected to line
power.
If
the annunciator stays
on,
the instrument requires
service.
If
the instrument
is
using an external
5 or 10
MHz
standard, the OVEN annunciator indication has no
effect
on instrument performance.
A-38
Assembly-Level Service Overall Instrument Troubleshooting
HP 8340B/41B