Fan Troubleshooting - Agilent Technologies 8753ES Option 011 Service Manual

Power Supply Troubleshooting

Fan Troubleshooting

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 Fan Voltages
If the fan is dead, refer to the A8 post regulator block diagram at the end of this chapter.
The fan is driven by the +18 V and −18 V supplies coming from the A15 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 A17 motherboard via pin 32 of the A8P1
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 A17 motherboard via pin 31 of the A8P1 connector.
Measure the voltages of these supplies while using an extender board to allow access to the
PC board connector, A8P1.
Short A8TP3 to Ground
If there is no voltage at A8P1 pins 31 and 32, switch off the analyzer. Remove A8 from its
motherboard connector (or extender board) but keep the cable A15W1 connected to A8.
(See Figure 5-5 on page 5-9.) Connect a jumper wire between A8TP3 and chassis ground.
Switch on the analyzer.
• If all the green LEDs on the top edge of A8 light (except +5 VD), replace the fan.
• If other green LEDs on A8 do not light, refer to "If the Green LEDs of the A8 Are Not All
ON" on page 5-13.
Chapter 5 5-19