Troubleshooting; Fhn Speeds; Check The Fan Voltages; Short Astp3 To Ground - Agilent Technologies HP 8719D Service Manual

The fan speed varies depending upon temperature. It is normai for the fan to
be at high speed when the anaiyzer is just switched on, and then change to low
speed when the anaiyxer is cooled.
Check the FIm Voltages
If the fan is dead, refer to the A8 post regulator block diagram (F'igure 5-7) 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,
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 A8Pl connector.
Measure the voltages of these supplies while using an extender board to aiiow
access to the PC board connector, A8Pl.
Short A8TP3 to Ground
If there is no voltage at A8Pl pins 31 and 32, switch ofi the analyzer. Remove
If aii the green LEDs on the top edge of A8 light (except +5VD), replace the
q
fan.
If other green LEDs on A8 do not light, refer to "If the Green LEDs of the A8
q
are not Ah ON" earlier iu this procedure
and
remains