HP ProLiant G7 Fan Header Configuration and Pinout (DL120 et al)

1U HP DL120 G7 servers will not boot with their fans disconnected from their proprietary motherboard headers. The original 40mm fans are actually two fans stacked; designed to have both running, but the server will still boot if one dies. iLO3 sees each fan group as 2 fans, a fan number (3-6 in my case) and an ‘A’ and ‘B’ fan.

The G7 Fan connector comes both in the ‘new’ way, a 2×3 6-pin header (G8 reportedly only has these) and the ‘old’ way (which is what all 4 of mine originally were) with a 1×6 6-pin header.

Key          |                    |
Typical      | Blk  Red  Wht  Blu |
Alternative  |      Yel  Red      |
Intel HSF    | blk  Yel  Grn  Blu |
               GND  12v  Tach PWM

Standard PWM case fan 4-pin:

1×6 6-pin header G7 Fan Connector:

Key |                              |
    | Org  Blk  Red  Blu  Yel  Grn | Wire Color 1
    |      Grn*      Wht	   | Wire Color 2
      12v  GND  12v  1.6v .7v  1.6v 
      FanB      FanA RPMa PWM  RPMb

If you wire two fans to each 1×6 connector, sharing the GND and the PWM signal, you’ll satisfy the system’s need to see fans to boot. You’ll also get variable speed fans depending on temperature. I my experience, the system doesn’t care about the RPMs, it just needs to know they’re spinning. Good thing because the 120mm fans generally spin nowhere near the 7000-9000 RPMs most 1U 40mm fans spin at.

Inspired by this forum post regarding G8 servers in particular: Faking the fan signal – Microserver Gen 8 – RESET Forums (homeservershow.com)

Here are a few photos of this in action. I sourced GND and 12v+ elsewhere on the board, so in the 2 connections you see the most I’m only connected to RPMa, RPMb and PWM. I’m using some (sparsely populated) 2.54mm spacing JST-XH connectors and a terminal block