Introduction: Cheerlux CL760 Fan Silencing
The fans in the Cheerlux CL760 are very loud (despite its claimed "quiet operation"). It is possible to make it much more quiet with some effort. Caveats up front; this isn't a drop-in replacement, requires soldering and parts and quite a bit of fiddling with the cables inside. It will run a bit hotter, which will probably decrease the lifespan. And it for sure voids any warranty.
This projector is rebadged as the Kogan "3200 Lumens HD Projector" (KAPRHD32LXA) which I have.
A quick review: it works and looks pretty good. It will not be usable in daylight, the focus isn't perfect on the edges and the blacks aren't all that black, the speakers are useless and buzz (I found turning the volume up, then back down to zero fixes that - if I open the case again I will disconnect them). I use it with a Chromecast and a HDMI audio splitter to send optical audio to a soundbar, which all works fine. For the price, as an occasional movie night projector in an upstairs area on beanbags for the family, it suits my purpose well.
I really had an issue with the fan noise, however. In the following, I replaced the 92mm fan for the LED heatsink with a Noctua 92mm NF-A9 FLX 1600RPM model, and cut the speed of the blower fan for the projector area.
- Noctua 92mm NF-A9 FLX 1600RPM
- 82 Ohm, 0.5 watt resistor
- Soldering iron
- Various heat shrink cables
Step 1: Opening the Case
Use a long Phillips head screwdriver to unscrew from the bottom of the case, then flip it over to pull off the top (section with the buttons). There are no clips or other retainers (other than the screws).
To replace just the 92mm fan and slow the blower fan, you do not have to remove the main board or pull the shroud off the projector section. I did, however, to see what was going on.
Step 2: Replacing 92mm Fan
The 92mm fan blows over the large heatsink for the projector LED. It can be lifted out and removed without tools.
The replacement Noctura fan comes with a range of PC compatible cables, but does not plug into the Cheerlux power supply. I took the supplied SATA adaptor from the Noctura fan which I would not need, and cut off the end that plugs into the fan and joined it with the existing cable cut from the Cheerlux fan.
I had to remove the silicone padding on the corners of the Noctura fan for it to fit. These might have been nice for vibration control, but the slot for the fan is tightly moulded.
Step 3: Slowing the Rear Blower Fan
The rear blower fan sends air through the shroud and into the internal reflector cavity.
To get a sense of its importance, I disabled it and the internal temperature quickly rose to over 100C. Clearly this fan should be running!
I found that some IC grabbers worked to power the fan without modifying the existing cable. I put this onto a linear power supply to be able to modify the voltage to the fan easily.
I found that at 6V (half the original 12V supplied), the fan was almost inaudible but the internal temperature wasn't exceeding about 30C. This seemed very reasonable.
The fan was unmarked so I do not know the rotational speed, airflow, etc. However, at full speed it drew about 146mA, giving an internal resistance of 82Ω. Because we just want to halve the voltage, this makes the calculation pretty easy; just double the resistance. However, working it out anyway:
V(fan) = i(fan)*r(fan)
V(target) = i(target)*r(fan)
6 = i(target)*82
i(target) = 73mA
V(drop)=i(target) * r(extra)
6=0.073 * r(extra)
r(extra) = 82Ω
This means the resistor will be dropping
Thus you want a 82Ω, 1/2W (minimum) resistor. I found my resistor ran at about 65C which is hot to touch, but should be OK.
I simply wired that inline with the blower fan as shown. With the lid back on after finishing everything the temperature maintained about 30C.
Step 4: Finalising the Noctura Fan
The Noctura fan comes with "low noise" and "ultra low noise" add-on cables which contain different levels of internal resistance to slow the fan.
I could definitely hear the difference between no adaptor and the low-noise version, but could not noticeably hear the difference with the ultra-low noise. Thus it seems best to keep the slightly higher airflow.
The Noctura cable is not terribly well positioned for this placement when the fan is orientated to blow outwards over the heatsink. I have run the cable underneath the fan and up the front, where it is certainly pinched much more than would be ideal around the moulding. It is, however, in a thick shield. Because of the case moulding, you would have to do some modification with a Dremil or similar to obtain a better cable path. You will also want to make sure you secure the extra cables to ensure it doesn't fall into the fan.
Thus with a bit of squishing, the lid can be put back on.
The heatsink temperature goes to about 55-65C during use. I think this will probably shorten the life of the LED over time; however given we use it for movie nights only sporadically this is not a major concern.
Step 5: Final Results
With the projector put back up, I am satisfied with the modifications. You can barely hear the projector in a completely silent room, and certainly not over even the quietest parts of a movie.