I upgraded my ageing Tektronix DS210 scope to Rigol DS1054Z and was rather unpleasantly surprised by the fan noise this thing emits. If you have one, then you know how hugely annoying it is. If you don't yet own one, then lets put it like that - you wont be able to listen to music at sensible levels with this thing running on your desk. It is really bad.
The scope itself is not some power-sucking beast that would require huge ventilation, it consumes something like 22W with all 4 channels running. Hard to tell why its designers thought that running the fan at full speed would be a good idea.
The typical approach is to put a 50 ohm or so resistor in series with fan to reduce its speed, but this may cause problems down the road when the ambient temperature is higher that normal room temperature or when the fan ages and will not start reliably with the resistor in series.
That is why I decided to do the whole thing - first replace the fan with a quieter one, and then hook it up to the scope board through my ATTiny based pwm fan controller. Without the programming connector, the piece of prototyping board is quite small, here is the stripped down schematics diagram:
And this is how the assembled board looks:
For the code, see the ATTiny based pwm fan controller project page.
Installation
You will need to get the scope open, it will void your warranty. Or you may want to cover your tracks and be very careful with a warranty sticker, see this video by Mike Harrison to learn how to get the sticker off in once piece. You will obviously need to do it again for undoing your mods before sending it in for warranty repair, or just leave a non-sticky paper on it, and tape the paper to scope so that you can easily get it open again.
The replacement fan I went for is Fractal Design Silent Series R3 50 mm. Compared to the Sunon fan in the scope it is super quiet, and would be a worthwhile upgrade even without the speed control.
The fan came with 3 pin connecter, but I did not need a tach output, so I just clipped that wire off close to the connector end, and slipped a piece of heat shring tubing over the wire to make sure the tach output is insulated. The connector itself I also cut off, and soldered the +12V and GND wires directly to the PWM controller board. For attaching the controller board to the scope main board I used the cable from the original fan, clipped it off close to the fan so that I can resolder it if need be, and soldered the wires to input side of the PWM controller. I then simply wrapped the controller board with electrical tape, keeping the chip free, and attached it to power supply shielding with couple of cable ties. That is how the end result looks:
When the scope warms up a bit, the fan kicks in and at normal room temperature stays running constantly at relatively low speed. The scope will not be totally quiet like my old fan-less Tektronix TDS210, but with any kind of ambient noise present it will be almost unnoticeable.