Music is a necessity while working on projects, and I got tired of not being able to hear it over my Tektronix TDS544A oscilloscope. As easy as it is to crank the volume higher, I wanted to address the problem at its source, the oscilloscope's built-in 24V fan.
Having had very good experiences with their 12V PC case fans and coolers, I was intrigued by Noctua's industrialPPC line, particularly the NF-A14 iPPC-24V-2000 Q100 140mm fan. The fan that came with the oscilloscope, a Comair Rotron JQ24F4V, used mounting holes that look nothing like those for a traditional PC case fan. Thankfully, I had plenty of space for a bracket to adapt one mounting pattern to the other, since replacing the fan bought me a whole 25mm of depth.
Initially I bought the 12V version of this fan by accident. In other circumstances, this would've worked fine using a buck converter to drop 24V down to 12V, but I wasn't interested in adding an electrical noise source inside a piece of calibrated test equipment.
When it comes to high-quality electronics, especially test equipment, specific components are usually selected for a good reason, and I'm sure this oscilloscope's fan was no exception.
It was probably chosen for its airflow rating above all else, based on the power dissipated by all of the other components inside the oscilloscope, with a safety margin.
With this in mind, there is some risk that swapping the original fan for a quieter one will result in components not being cooled adequately, shortening their useful lifespan.
All told, this is a relatively simple design and an excellent project for OpenSCAD. One side features counter-bored holes to accommodate the fasteners for the original fan, and the other side features countersunk holes for the fasteners that came with the new fan.
|Filename + Description
OpenSCAD 3D Model
Fan bracket 3D model
STL 3D Model
Fan bracket 3D model
|Name + Description
tek-fan-bracket Git repository
As admonished at the top of this page, my biggest concern in doing the fan swap is whether the replacement fan can move an adequate amount of air to cool the oscilloscope's internals.
I could only find a datasheet for a similar Comair Rotron fan (JQD24U3E2), which specifies 332 CFM, or 563 \(m^3 / h\) at 64 dBA. Compared with the Noctua's 182.5 \(m^3 / h\) at 31.5 dBA, there's roughly a 1000x decrease in noise1 for a 3x decrease in airflow.
Performing a very subjective test involving placing my hand over the exhaust vent on the oscilloscope's side, I couldn't tell the difference in airflow between the original and replacement fans. Unfortunately, only time will tell if there are any long-term issues.
Someone looking to reduce the noise level of their own TDS-series oscilloscope doesn't necessarily have to use this Noctua fan. The bar is pretty low for improving the noise level and there are plenty of 24V 140mm fans available that move more air while still being quieter than the original. I chose to maximize noise level improvement, since the oscilloscope was the worst offender out of all of my regularly used equipment.
I don't have any reason to revisit the bracket that this project was focused on - it works exactly as intended - but I may swap the replacement fan again in the future, even if only to sleep better at night.
In an earlier version of this page, I made the classic mistake of treating sound pressure measurements as linear rather than logarithmic when comparing the two fans. That being said, I'm not sure comparing 1000x vs 3x are really illustrative of the functional gains/losses of the fan swap. ↩