Fan Troubleshooting
Fan
Speeds
The fan speed varies depending upon temperature. It is normal for the fan to
be at high speed when the analyzer is just switched on, and then change to low
speed when the analyzer is cooled.
Check the
Ran
Voltages
If the fan is dead, refer to the
A8
post regulator block diagram
(F’igure
5-8) at
the end of this chapter. The fan is driven by the + 18 V and -18 V supplies
coming from the
Al5
preregulator.
Neither of these supplies is fused.
The -18 V
supply
is regulated on A8 in the fan drive block, and remains
constant at approximately -14 volts It connects to the
Al7
motherboard via
pin 32 of the
A8Pl
connector.
The + 18 V supply
is regulated on A8 but changes the voltage to the fan,
depending on airflow and temperature information. Its voltage ranges from
approximately
-
1.0 volts to + 14.7 volts, and connects to the
Al7
motherboard
via pin 31 of the
ASP1
connector.
Measure the voltages of these supplies while using an extender board to allow
access to the PC board connector,
A8Pl.
Short ASTP3 to Ground
If there is no voltage at A8Pl pins 31 and 32, switch off the analyzer. Remove
A8
from its motherboard connector (or extender board) but keep the cable
A15Wl
connected to
A8.
(See
Figure
5-5.) Connect a jumper wire between
A8TP3
and chassis ground. Switch on the analyzer.
q
If
aII
the green
LEDs
on the top edge of A8 Iight (except
+5
VD), replace the
fan.
q
If other green
LEDs
on
A8
do not Iight, refer to “If the Green
LEDs
of the A8
are not all ON”
earlier
in this procedure.
5-22
Power Supply
Troubleshootins
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