Nomos,
You haven't been very clear regarding what you are actually trying to accomplish - what you think is wrong and needs fixing. Please restate in terms of your goal(s) for wanting to make any changes.
If you simply want to manually control a fan (i.e. set them to a fixed duty cycle), you can change the Control Mode to Manual and then use the Minimum Duty Cycle parameter to select the duty cycle that the fan will run at.
In the case of the Processor Fan (and any other fan header that has a 4-wire PWM-controlled fan attached), you need to take into account what type of duty cycle response is implemented within the fan. Every fan has a minimum duty cycle that it can reliably maintain. The 4-wire fan specification (available here: http://www.formfactors.org/developer/specs/4_Wire_PWM_Spec.pdf) details three ways that the fan is allowed to respond to duty cycle settings that are below this minimum:
- (Type A) As the duty cycle drops below the supported minimum, the fan will continue to operate as if the duty cycle was set to its supported minimum (i.e. it does not slow down any further).
- (Type B) As the duty cycle drops below the supported minimum, the fan will continue to operate as if the duty cycle was set to its supported minimum. When the duty cycle reaches 0 (zero), however, the fan will stop spinning altogether..
- (Type C) As the duty cycle drops below the supported minimum, the fan will attempt to slow down accordingly. At some specific duty cycle, the fan will be unable to maintain spin and will stop.
The Zalman site's information is anemic; they don't say anything about minimum duty cycle or operational mode. The unit's thermal dissipation is top notch, however, so if your concern is that you never see the fan speeding up, it's likely because... it doesn't need to! You mentioned not being able to get the speed to go down to 800RPM. The reason for this is that this fan's minimum speed is listed as 900RPM. Unless it is a Type C fan - which is pretty rare - you are not going to be able to get it to run at 800RPM; it just won't go that low!
I also checked the Coolink site; same story; they don't publish this information either. Spec-wise, though, these look like really good quality fans. I recommend that everyone use 4-wire PWM-controlled fans, so good choice there...
...Scott