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Noisy HP 54622D scope, way too much fan noise.

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PlaneSailing:
I have an Agilent 54622D which works great - except for the fan noise, it's too loud, am asking if anyone has advice or hopefully a fix.

The fan is a Panasonic FBA08A12U spec'd at 12V 0.36A 47CFM and 38dBA.  I have tried mounting the fan on rubber grommets, the smallest I could find at my local ACE hardware.  Drilled out the fan mounting holes to the 1/4" grommet groove diameter, cut the grommet in 1/2 as it was not deep enough, and did not overtighten the 3 mounting screws.  Please see picture for detail - top mounting screw removed for clarity. This had no effect on the noise (I have a sound meter), and don't think the fan frame is "hitting" the case.

Sounds like I need a replacement quieter fan - any suggestions ?, thanks.

T3sl4co1l:
And, is it not just bearing noise -- needs at least a cleaning, preferably replacement?

I don't recall those scopes being particularly noisy, though it's been a while since I used one.

Better way to work with the fan, probably: take it out and power with a bench supply or whatever.  Hold it against the table, does it vibrate significantly (table as a sound board)?  Does it change if you press on the rotor (watch your fingers!!), or move it around or whatever?  Is it buzzing at the rotational rate, or a harmonic (blade noise), or more generalized (white noise, the rushing of turbulent air)?

Replacements are easy, anyways; even if it's not a standard size, it's probably awfully close to one.  Check drawings for bolt holes.  Probably safe to use somewhat less CFM, or higher (say 30+?), I don't know that those things got all that hot inside?  Otherwise, equal or greater to be sure about it.  And just being ventilation, output pressure shouldn't be a concern.  Can opt for ball bearings (or air or magnetic as the case may be?) for long life, and datasheets/supplier catalogs usually list acoustic noise even, so you can sort by that.  Blade noise depends on shape, so there's some room to control that while keeping CFM up, but generally speaking higher CFM will of course be noisier, so you can't be too picky at some point.

Tim

PlaneSailing:
Thanks for the advice, I took the existing Panasonic fan out, ran it off 12V on the bench, and it's just "white" noise.

Thinking the Noctua NF-R8 redux-1800 would be a good replacement ($10 at Amazon in the US March 2022), but it's 31CFM air flow is lower than the original Panasonic's 47CFM, which has me a little anxious. Possibly the original Panasonic was just 20 years ago HP "over engineering" (which is generally a great idea) ?.
Be interested if anyone has swapped out the fan in an HP / Agilent scope or logic analyzer, thanks.

sorenkir:
Hi,
I have replaced my Panasonic fan with a used PAPST 8412NGML a few years ago.
The air flow is lower, but the noise also !
I haven't had any problem so far.
Michel.

T3sl4co1l:
The most direct consequence of less airflow is likely higher part temperatures, so, a lower maximum ambient before those parts reach their absolute limits in turn.  Basically, as long as your lab is habitable it's probably not going to matter.

Tim

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