Thermal Sensing And Cooling - HP Compaq d330 DT Technical Reference Manual

Chapter 4 System Support

4.7.4 THERMAL SENSING AND COOLING

All systems feature a variable-speed fan mounted as part of the processor heatsink assembly.
Desktop and Configurable Minitower systems provide an auxiliary chassis fan. All fans are
controlled through temperature sensing logic on the system board and/or in the power supply.
There are some electrical differences between form factors and between some models, although
the overall functionally is the same. Typical cooling conditions include the following:
1. Normal – Low fan speed.
2. Hot processor – ASIC directs Speed Control logic to increase speed of fan(s).
3. Hot power supply – Power supply increases speed of fan(s).
4. Sleep state – Fan(s) turned off. Hot processor or power supply will result in starting fan(s).
Figure 4-12 shows the fan control circuitry for desktops and minitower units. The RPM (speed)
of all fans is the result of the temperature of the CPU as sensed by the Control ASIC and indicated
to the Speed Control circuitry. The fans are controlled by circuitry to run at the slowest (quietest)
speed that will maintain proper cooling. NOTE: Units using chassis and CPU fans must have
both fans connected to their corresponding headers to ensure proper cooling of the system.
CH Fan Sense
CPU Fan Sense
I/O
Controller
PS Fan Sense
Processor
Figure 4-12. Fan Control Block Diagram
4-28 hp compaq d330 and d530 Series of Personal Computers
Featuring the Intel Pentium 4 Processor
+12 VDC
CH
Fan
Sense
CH
Fan
Control
CH Fan
OVR RD
ICH5
Fan Clamp
Speed
Control
Fan Speed
Control
ASIC
First Edition – June 2003
Ch as sis Fan
He a der P8
CPU
(-)
Fan
1
Sense
(+)
2
PWR
3
PS Fan
Sense
CPU Fan
H ade e r
P70
(-)
1
(+)
2
CPU
PWR
Fan 3
Control
P16
Fan CMD
Power
1
Supply
Fan Sns
Assembly
2