technobeam fan issue

I've got a tech the fans not running, when I test the pins on board I get 0v. I test with meter grounded to chassis and pos to the pin I get 23.94v, so when I ground the neg lead of the fan the fan works! seems like a simple fix, does anyone have any concerns or issues with this?
  • Without looking to see how fan control works on this fixture, you may well be bypassing fan control/monitoring completely . . . (some devices control the low side of things . . . IE, the fan may be wired to +24 directly, and the control on the return.).

    If it was me, I'd look at the schematics, and figure out what it's supposed to be, and repair accordingly. Nothing I hate more than getting into gear and finding hack fixes when doing it right would have likely only been minutes more time.

    (I couldn't not look . . . schematics clearly show the fan wired to +2, and controlled by Q5 on the board, an MPSW01 transistor (NPN, fwiw) to ground. Buffered by U11F, three resistors, and one cap. IE, replacing the whole smash would likely cost you about three bucks . . . . but probably just the transistor. Oh, and I looked at the 1.6.1 logic card, but all are on line, and should be pretty much identical in that area).

    - Tim
  • This is usually a bad Q5, which takes the fan low to turn it on. Short the E-C together and if the fan comes on, and there is a Fan_En signal present at the base, then Q5 is shot an needs to be replaced. This is not uncommon for TBeam.
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