We have a HP Pavilion DV3 4000SB that was given an error on startup that the fan was having problems (System Fan 90b error message)

So I decided to open the laptop up and clean the fan, as that seemed the easiest option. Upon opening it up, at first I froze and thought "No wonder! The whole thing's burnt!", but then I started thinking it looked more like someone used a spraycan on it.

I looked up a video on youtube of someone disassembling his Pavilion and noticed there wasn't any of the black on his, so my question here is: Have any of you encountered this, or know what it is? Or if it's something that could point to a problem?

Photograph of the heat sink

  • Note that, although the fan didn't seem very dusty, I cleaned it with a can of pressurized air, reassembled it and let the laptop run some heavy activity, and it didn't shut itself off (which it did previously) - but I'd really like to know more about this
    – arnehehe
    Nov 12, 2013 at 16:22
  • Looks like it was sprayed with paint to me. As far as the dust, it's possible there was a small piece of dust blocking one of the air paths or hindering the fan's ability to spin.
    – rob
    Nov 12, 2013 at 16:25
  • Was this laptop new or used when you purchased it? This does not look something HP would do.
    – Ramhound
    Nov 12, 2013 at 16:26
  • The black paint increases the emisivity, and thus the radiative cooling. See en.wikipedia.org/wiki/Heat_sink#Surface_color
    – mpy
    Nov 12, 2013 at 16:40
  • @mpy "The black paint increases the emisivity" -- Black color is not the same as black paint. Paint is a coating that is much less heat conductive than metal, and the coating could negate any benefit of its color, black or anything else.
    – sawdust
    Nov 12, 2013 at 18:41

1 Answer 1


As a computer technician I can tell you this looks completely normal, what the others said about emissivity. The best way to determine if its in fact burn residue would be to remove the heat sink and scrub it with isopropyl alcohol.

However, you should also keep in mind that if the cpu was able to get so hot it burned residue on the heat sink, the pcb itself would be obviously and severely damaged.

Oh yea, the fan issue. Continue on your course of action, good first step. If that doesn't resolve the fan error message, consider replacing it. Fans go out...like hard drives, it just happens. Probably $15 on amazon and should be relatively easy for you to replace since you already know how to open it.

  • So it helps out with the cooling, that's interesting. I guess these physics effects go beyond my IT knowledge, but it's definitely interesting to know :). After cleaning out the fan, should the problem return or persist, I will definitely get a new fan for it. Thanks
    – arnehehe
    Nov 13, 2013 at 10:48
  • If after you've cleaned the fan and the issue returns or persists, replacement would be necessary. Also, emissivity in thermodynamics is just a fancy way of explaining the same concept people say you shouldn't wear black on a hot summer day - it naturally absorbs. Obviously your situation is a little different but close enough.
    – Joe
    Dec 2, 2013 at 0:06

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