Compaq 850 manual Temperature Sensing and Cooling, Cmd

Chapter 4 System Support

4.7.4 TEMPERATURE SENSING AND COOLING

These systems feature a fan integrated into the power supply assembly. A separate chassis fan is also employed. Both fans are variable-speed type, and typically operate in tandem as long as the power supply is active (producing 12 VDC). The fans are off in S3 (Suspend-to-RAM) and S5 (Soft-Off) states.

NOTE: These systems are designed to provide optimum cooling with the cover in place. Operating a system with the cover removed may result in a thermal condition of system board components, including the processor.

Figure 4-11 shows the fan control schematic.

Chassis Fan

Header P8

SMBus

ICH2

Processor

Sensing

ASIC

			(+)	4	4	(+)
		CH Fan CMD (-)				(-)
				3	3
				2	2
Fan
Sense [1]	On/Off	P1			Power Supply Assembly
	Control
		24
						PS Fan	PS Fan
					Speed
Fan CMD		12				CMD	(-)
			Fan		Control
Fan Off-						On/Off	(+)
		8	Off
Therm-	82801					Control
	ICH2

NOTE:

[1] Will be +12 VDC if chassis fan is connected and operating.

Figure 4-11.Fan Control Block Diagram

An ASIC monitors a thermal diode internal to the processor and provides a Fan CMD signal that the Speed Control logic of the power supply uses to vary the speed of the fans through the negative power rail. The turning off of the fans as the result from the system being placed into a Sleep condition is initiated by the ASIC asserting the Fan Off- signal, which results in the On/Off Control logic shutting off the +12 volts to the fans.

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 – Fans turned off. Hot processor or power supply will result in starting fans.

4-34Compaq Deskpro EXS and Workstation 300 Personal Computers

Featuring the Intel Pentium 4 Processor

First Edition - December 2000