06.09.15

My second-generation Drobo started sounding like a jet engine recently. I disconnected the 4-drive device and pulled each of the drives out, one-by-one, thinking that one of them must be going bad. Once the Drobo was empty, and the sound was still going, I figured that the fan had gone bad. The Drobo has been in service since 2009, so 6 years isn’t too bad for longevity of that fan, but it was a bit disappointing. I’ve considered getting a second Drobo for redundant local backup, but at this point I figured I’d look at what it would take to replace the fan myself.

Note: I am in no way an electrical engineer. I have a fun time taking things apart, but putting them back together is a roll of the dice. However, the noise wasn’t going to go away and as it sits under our TV, it wasn’t making for a pleasant home life. I decided to look for information on replacing the fan. Fortunately a few other more intrepid adventurers had already done a bunch of leg work, such as Samuel Tannous, and I want to re-iterate his thank yous:

Firstly a huge thank you to everyone who commented on this thread (http://www.drobospace.com/forums/showthread.php?tid=1608) on the Drobo forums, especially DroboLars for posting clear steps on how to replace the fan and j_hah for posting alternative fan options with specs, both on page 2.

As Samuel was working with a Drobo FS and I was trying to fix a standard 4-bay Drobo (no suffix) I knew there might be some differences, but I was able to work out that the fan recommendation he made was the correct size (92 mm), but as this is a few years later, I needed to order a newer model. The Noctua NF-B9 was under $20 at Amazon.

The larger issue for fan replacement is that the Drobo uses a simple two wire connection: a 12v (red) and a ground (black). More modern fans seem to have three or four connectors (for sensors and speed control). Fortunately, the user “blowhard_uk” posted to a Tom Hardware forum with the following chart of fan wire connections:

2 pin fan header
Black = Ground Red = +12V

3 pin fan header
Black = Ground Red = +12V Yellow = Sensor

4 pin fan header (per Intel, cirac 2005)
Black = Ground Yellow = +12V Green = Sensor Blue = Control

I’m guessing that these are all industry standards, but I can’t find any specific documentation for the two and three pin versions (which have likely been around for decades).

The biggest difference between the FS and my 2nd gen was that there was no power connection to disconnect when disassembling the device. Looking back, the tools I used were a medium sized Philips screwdriver, a wirecutter with wire stripping holes, and come electrical tape. So my steps were:

Disconnect the power and the computer connection (of course).
Pop out all the drives.
Remove the 5 screws on the bottom of the case.
Remove the magnetically-attached front cover and unhook and remove the plastic fascia from the front.
Partially slide apart the interlocking pieces of the chassis, but watch for the fan connector.
Pull the fan connector off the circuit board.
Finish pulling the chassis pieces apart. One portion has the circuit board with LED lights at one end. The other half has the fan.
Remove the back plastic cover on the fan portion. There are four clips in plastic that hook the back panel to the chassis. One of them is very tough to unhook, but it can be done.
Use a long-shaft screwdriver (Philips works best) to push down the central stems of the plastic clips holding the fan in place at each corner. (These are used instead of screws because they handle the vibrations better.)

Now came the most difficult part: getting the wires cut and spliced together. I used a wire cutter to cut the white plastic header plus about 4 inches of wire from the old fan. I stripped off about an inch of the insulation of the wire from the black wire and the red wire.

I set that aside and opened the new fan. It had a few different extension cables, so I took one of them and clipped off the very end with the 4 pin plastic header that would normally attach to a motherboard. I was able to pull apart the 4 individual wires in the cable and stripped off the insulation from the black and yellow wires.

Now I had two cables, one with a two-pin plastic header and one with a 4 pin plastic header. I then twisted together the exposed wires from the black wires and taped the twist with electrical tape. I did the same with the red wire from the old fan and the yellow wire from the new fan’s cable. Now I had one cable with the proper plugs on each end.

Then it was largely a process of working backwards through the same steps to put everything together. I tested it out to make sure the fan was blowing OUT of the box and then put all of the drives back in and plugged it back into the Mac. It’s been running just fine since.

I hope I’ve added another couple of years to the life of this Drobo. But I really should be looking at getting a second one.

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