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Fault Indicators
The HP 70001A has three fault indicators. While these indicators are located in the mainframe,
problems external to the mainframe can cause the indicators to turn on. External problems
should be investigated before troubleshooting the mainframe.
VOLT/TEMP
If this fault indicator is on steady, check for the following problems before
deciding the mainframe needs repair.
Temperature
limits
Low input
voltage
Note
Very long ac wiring runs may cause the ac power voltage at the mainframe to
drop below an acceptable limit, when the mainframe applies its load to the ac
line. This will cause the mainframe to cycle on and o . No damage will occur
as a result. The cure is to correct the power wiring or voltage.
1
Keep in mind that the internal temperature of the instrument will change with a
corresponding change in the ambient room temperature, and that there is a delay between
a change in ambient temperature and a change in internal temperature. It can take 20
minutes or more for an overheated mainframe to cool internally to an acceptable
temperature, since no cooling air is being moved by the fans when the supply is shut down.
5-2 Troubleshooting
Excessive ambient temperature, exceeding 55
VOLT/TEMP fault indicator to come on and stay on. Move
the mainframe to a cooler environment and wait for the
temperature to decrease to the normal operation range.
the temperature decreases the mainframe will restart itself.
If the indicator goes out after the mainframe has cooled the
mainframe is probably not at fault.
If the problem persists; when the mainframe attempts to restart
itself, verify that both cooling fans are operating by checking
the air
ow into both of the rear-panel fan-intake openings of
the mainframe.
If the line voltage is low or the voltage selector setting does not
agree with the input voltage, the VOLT/TEMP fault indicator
will come on. Check the ac input voltage and set the voltage
selector switch as follows.
115 V
position for 90|132 Vac line input voltage.
230 V
position for 198|264 Vac line input voltage.
If the low voltage condition is corrected, the unit will restart
itself.
A
ashing VOLT/TEMP fault indicator can be caused by an
impedance mismatch between the ac line and the mainframe
input. This usually occurs only at extremely low temperatures
(below 0
C). The cold input thermistors (now a high impedance)
reduce the line voltage. An under voltage condition is sensed
and the mainframe shuts o . The reduced load allows the
sensed line voltage to rise and the unit turns back on.
C will cause the
When
1
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