Reducing power supply noise on HP N40L Microserver

Two years ago I purchased a HP N40L Microserver to use as offline backup storage to backup documents, photos and other personal files.  The device only gets powered on for short periods while I send or retrieve data from it so I was not originally overly concerned with the fan coil noise I noticed coming from the Microserver's power supply.

Fast forward two years and I had grown tired of the high pitched coil noise even though it was so infrequent.

So I pulled out the power supply, made by Delta Electronics, and removed the fan for inspection.

My Fan has the current specifications:

Manufacturer: T&T
Model:         4020TH12B-PD1
Voltage:       12VDC
Current draw:  0.28A
Size:          40x40x20mm
Pins:          Two
Search Google for this fan

After searching the internet for some time I discovered this may also be sold by Cofan USA with the following specifications:

Manufacturer:            Cofan Usa
Model:                   F-4020TH12B III
Rated Voltage:           12V
Operating Voltage:       8-13.8V
Rated Current (A):       0.28
Actual Current (A):      0.10
Rated Power (W):         3.36
Rated Speed (RPM):       9000
Max Air Flow:            0.31 CMM or 10.90 CFM
Max Static Air pressure: 9.79 mmH₂O or 0.39 InH₂O
Noise level (dBA):       34.90



Searching the internet and not wanting to spend $20-30 on a fan I managed to find a near match on element14.com for $7 specifications below:

Manufacturer:         Multicomp
Model:                MC36287
Fan Frame Size:       40mm
External Depth:       20mm
Supply Voltage:       12VDC
Current Rating:       115mA
Rated Power (W):      1.38
Rated Speed (RPM):    8200
Flow Rate - Imperial: 10.8 cu.ft/min
Flow Rate - Metric:   0.305 m/min 
Static Air pressure:  0.27 InH₂O
Noise Rating:         27.5dBA
Bearing Type:         Vapo


Now with the multicomp fan there are three "issues" that you need to understand or need to resolve.

The first is that the fan comes with bare leads so you need to cut the connector off the old fan and resolder onto your new fan.  Make sure you use some heatshrink tubing or the like and not cheap electrical tape as the fan power wiring comes close to heatsinks and electrical tape is just going to come free after some time.

The second is the screws on the original fan do not fit the Multicomp fan as the mounting holes in the original T&T fan are smaller than those in the Multicomp.  This is not a big deal as the case lid of the Delta Electronics power supply is well designed and pushes up against the fan to eliminate any vibration that would result by the fan not being screwed into the power supply.

The third and last is the fan power cable routing, the Multicomp fan does not have notches cut into both sides of the housing to route the power cables neatly.  To fix this you can use a dremel or other cutting tool to cut a notch, but I found I was able to route the cable in such a fashion that cutting was not required.  This meant the cabling was slightly interfering with the power supply when it was reinserted into the Microserver's chassis, but as there will be no real vibration and I hope to never remove the power supply again I was not concerned.


After reinstalling the power supply and powering on the server I could not believe the difference.  This modification was well worth the hour or so it took completing as well as the $7 and 5 day shipping delay for the fan.

I honestly wished I had performed the swap earlier and even though I may could have initially claimed this issue through HP warranty the shipping and headache declared this not an option for me.




Please drop me a comment if you have found this post useful or if it requires more information.