Fan tachometer reading of 0 RPM although fans are spinning, results in critical alert

Hello,

I have a problem with the server mainboard S1200SPL.

Quick information about the setup:

• board resides in a non Intel chassis
• 2 chassis fans (PWM)
• 1 cpu fan (PWM)
• BIOS, FRU and SDR are up-to-date
• SDR was configured with other chassis option, fan 3 and 4 installed, also CPU fan installed option
• Fans are set to acoustic mode in BIOS

Problem description:

• all fans are marked as critical in the web frontend (red)
• diagnostic lights blinking amber
• fan speed reading of all three fans is 0 RPM
• but all three fans are actually spinning at a low level

What I did so far:

• changed values in SDR file and uploaded them to mainboard
• "SDR Type C0/0A Records For Fan Sensor Scaling", section "OTHER"
  • values for fan 3 and 4 changed from 25000 RPM (hex: A861) to 1000 RPM (hex: E803) and 1500 RPM (hex: DC05), that are the new max values
  • value for processor fan changed from 25000 RPM (hex: A861) to 1900 RPM (hex: 6C07), that is the new max value
• "Fan tachometer sensors", "OTHER" sections
  • "OTHER_FAN_3"
    • M=04h
    • Nominal Reading=80h (500 RPM)
    • Normal Minimum=7Ch (490 RPM)
    • Lower critical = 00h
    • Lower non-critical = 02h
  • "OTHER_FAN_4"
    • M=06h
    • Nominal Reading=7Fh (750 RPM)
    • Normal Minimum=66h (600 RPM)
    • Lower critical = 00h (0 RPM)
    • Lower non-critical = 11h (12 RPM)
  • "OTHER_PROC_FAN"
    • M=07h
    • Nominal Reading=49h (550 RPM)
    • Normal Minimum=43h (500 RPM)
    • Lower critical = 2Fh (350 RPM)
    • Lower non-critical = 35h (400 RPM)

The values of fan 4 were set to nearly 0 to test if the critical alert will go away, but it didn't. Sometimes fan 4 reports a valid RPM value of 400 RPM and status gets to normal. The fans are spinning in a slow mode so that the whole system is very quiet :-).

Questions:

• are the fan readings influenced by some other values directly or indirectly in the SDR file, for example "Domain/Profile Dependent RECORDS" or the curves?
• can the fan readings be fixed somehow?

A bit history: the chassis that I bought came with 3 3-pin-only-fans, that spinned up to 100%. The cpu fan was always a 4-pin fan. Before I changed the numbers in the SDR file the 3 chassis fans got a valid rpm read, but the cpu fan did not. After setting the values in the SDR file, the cpu got also a valid RPM value, but the chassis fans were spinning at 100%. I decided to exchange two of the chassis fan through 4-pin fans. The third chassis fan is disabled now. After placing the new fans in, all rpm values were set to 0 RPM and the status became critical although all fans are actually spinning. and the max rpm values are the same as before After that I lowered the critical values for the chassis fans but without any success.