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FAULT
(amber) annunciator lights when one of the internal circuits performs atypically. To identify the
affected circuit, press
[SHIFT] [MANUAL]
which will cause "FAULT:
CAL KICK ADC PEAK TRK'' to
appear in the ENTRY DISPLAY. The flashing letters identify the faulty circuit as CAL (calibration
constants), KICK (YO or YTM kick pulses), ADC (analog to digital converter), PEAK (power peaking),
or TRK (tracking control); at this point the In Case of Difficulty section of this manual should be
consulted for further instructions.
EXT REF
(amber) annunciator lights when an external frequency source is used as the reference
standard instead of the internal crystal oscillator. The internal/external frequency standard is selected
by a rear-panel switch; see Figure 3-18 for an explanation of this switch and the associated connec¬
tors.
OVERMOD
(red) annunciator lights when excessive positive or negative voltage is applied to the front
panel FM MODULATION INPUT or when excessive negative voltage is applied to the front panel AM
MODULATION INPUT. In the case of AM, this excessive negative voltage causes the HP 8340B/41B
to attempt to exceed the maximum modulation depth. This happens at approximately —1 volt AM
input. Positive excursions have no limit as long as maximum available power is not exceeded, at
which point the UNLEVELED annunciator lights. AM linearity will suffer for inputs above +1 volt. As
with the UNLEVELED annunciator, an OVERMOD indication may signify an internal malfunction. The
OVERMOD condition can be caused by an FM input signal which significantly exceeds a Modulation
Index (peak deviation in MHz/modulation in MHz) of 5.
SRQ
(amber) annunciator lights when a remotely controlled HP 8340B/41B initiates a Service Request
(SRQ does not apply to local operation). Several conditions can cause a Service Request, including
altered parameter values, syntax error, power failure, and unleveled power. The SRQ annunciator
remains lighted until the computer sends an acknowledgement signal to the HP 8340B/41B. Service
Requests are more fully explained in the HP-IB Programming part of this Operation chapter, and in the
In Case of Difficulty section.
OVEN
(red) annunciator lights when the oven for the reference crystal oscillator is not at operating
temperature. A cold oven typically requires 5-30 minutes to reach operating temperature. The
STANDBY position of the POWER switch maintains power to the oven heater, thus keeping the oven
warm and the crystal oscillator ready for immediate operation. Although the HP 8340B/41B can be
operated with a cold crystal oscillator, the instrument might not fully comply with specifications until
the proper operating temperature is achieved.
UNLK
(red) annunciator lights when the HP 8340B/41B's output signal is no longer phase-locked to
the 10 MHz reference oscillator. Press
[SHIFT] [EXT],
which will cause "OSC:
REF M/N HET YO N2
N1" to appear in the ENTRY DISPLAY. The flashing letters indicate which oscillator is not phase
locked. Refer to the In Case of Difficulty Section.
DIAGNOSTICS
Press and hold
[INSTR PRESET]
to light the seven annunciators, then release
[INSTR PRESET]
and
press
[SHIFT] [FREE RUN]
which will light every LED segment and show the entire ENTRY DISPLAY
character set. Press
[INSTR PRESET]
or cycle the POWER switch to end this diagnostic routine. (This
diagnostic also tests the three other displays.)
NOTE:
[INSTR PRESET]
will restore the instrument to its standard starting condition. Cycling the
POWER switch will restore the instrument to its previous state.
Figure 3-6.
Entry Display (2 of 2)
3-18
Operating Information
HP 8340B/41B
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