Working a lot with my Blade 150 called “Sparky2” recently, the CPU fan turned out to be too loud, still. So I dug deeper into the matter and it turned out easier than I thought…

SUN -for whatever reason- decided to put a comparably small 40x40mm fan on top of the non-standard heatsink and additionally placed some aluminum spacer around it.
Removing everything revealed a totally standard PGA 370 socket! That’s Pentium III, if you remember… So a quick check in my old-junk-stash resulted in 3 nice heatsinks. I took the full-copper one and mounted a 60x60mm fan on top.
Put everything into place – done (BTW: SUN didn’t use any thermal grease, so did I)… but the bigger fan was still too noisy at 12 volts  🙄

After checking the fan also starts at 5 volts, the decision was clear: Bigger, massive copper heatsink plus bigger fan should be sufficient at lower revs.
There’s no direct 5V source on the Blade 150 motherboard. So I chose the vacant connector for the optional 2nd hard-drive (the closer floppy connector would do, too – but I had no spare cable to salvage).

Simply connecting the fan there wasn’t enough. OpenBoot actually checks for the fan tachometer signal and refrains from booting the system without one connected.
I was already evaluating how to build a signal dummy (a simple 555 timer circuit) when I decided to check if a simple forking out of the signal is enough. So I used a 2-wire cable and put ground and the tachometer signal to the on-board fan connector… and voilá that made the OpenBoot happy. Finally silence!

Here’s a piccy.

• Purple arrow: The new & bigger heatsink (the old on lies on to of the case, so it looks bigger than it actually is)
• Red arrow: The original fan connector (it still misses the tachometer signal bypass in this photo)
• Green arrow: This is where the new fan is connected.