Sorry for digging up this old thread. Since the beginning of owning my SDS1104X-E I have always been annoyed by the fan noise. It's not overly loud but just generally annoying for a small home lab and I found myself switching it off as soon as I could in between measurements.
Well, fast forward almost 4 years and since I well and truly own this piece of equipment now I decided to do something about it.
It’s been a while since the last post but I hope this might be of use to some.
After a few months I finally gave up and opened the scope. My idea was to measure critical temperatures and characterise the fan performance based on its voltage – when the scope is fully closed. I attached 3 probes (DS18S20) to the power supply heatsink, FPGA heatsink, and one “loose” inside the case. The probes are attached using double sided heatsink thermal tape, which is quite strong. Additionally, I placed one more probe a few cm from the inlet fan.
Next, I hooked up the SLA1016 logic analyser to give the setup more power draw. I also switched all channels, analog and digital on.
I programmed the SPD3303 to 5 1h slots. Started with 8V increasing it by 1V every hour. Below you can see the graph. I also attached the scope placement. There is not much air movement in the corner.
Looking at the data I take it’s safe to under-volt the fan. I believe I’ve read the operating temperature is up to 40 deg. Here in North-East England, where I live there is rarely above 25 deg outside. Plenty of headroom in my view.
I’m settling with powering the fan with 9V. The noise is much-much lower and bearable. I can barely hear it and it’s not annoying. Besides, it's easy to stick a standard, linear regulator without risking noise from a buck regulator.
I’m planning to do similar experiment with the SDM3055 and STD1062X soon. Can’t stand them fans!
P.S.
I just spotted a mistake. The last slot should be 9V.
After seeing the excellent post by AdiGital, I added a LM7809 on a small board with some JST XH connector so it is easily revearsable. There is plenty of space next to the fan so I mounted it with some high strength double sided tape. It rarely gets above 30C here and when it does both me and my trusty SDS1104 will be out of commission anyway.
The fan is still audible but sounds a lot more like a normal PC idling instead of the RGB gamermode beast it was before. I can definitely recommend it if your SDS1104 is out of warranty anyway and you don't live in a tropical climate. Thanks to AdiGital for doing the measurements and giving me the confidence to do something I should have done years ago.