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17 Jan 2022

Drobo b800fs Fan Replacement

One of my minor hobbies is that I am an inveterate dumpster-diver. Particularly in the suburbs around DC, where defense contractors pop up and disappear with the regularity of dandelions, you can find some pretty great stuff in dumpsters, or just sitting next to them, behind office buildings.

A few years ago I scored what I thought was a great find: a Drobo b800fs “storage appliance”, just leaning up against a dumpster alongside some ripped-out Ethernet cables and CRT monitors. Naturally, I grabbed it and took it home.

It took me a while to find enough drives to populate it, and then longer to download the “Drobo Dashboard” software and get everything working on my main desktop computer. But eventually, I had it all working. And then… it started making some really awful sounds. Based on previous experience with old junk, I knew one of the cooling fan bearings had probably failed and needed replacement.

Although there are plenty of guides around for opening up and repairing other Drobo models, I couldn’t find much about the b800fs in particular. So for the benefit of anyone else who may find themselves with one of these oddball machines, here are some notes on how I replaced the fans. Hopefully it will be of use to someone, someday.

Taking it apart

First, shut the unit down remotely from the Drobo Dashboard utility. Then, after it has time to completely turn off and spin down, unplug the Ethernet and power cords. It’s quite heavy when fully loaded with drives. Set it on a work surface and remove the front cover, which is held on with magnets (clever, really). If you remove the drives, mark them carefully so you can put them back into the same positions. (I did not remove them, because I like to live dangerously.)

After turning it upside down, remove the 4 small Philips head screws nearest the outer corners. You do not need to remove the rubber feet, as you apparently do with some other Drobo models. Turn it back over to normal orientation, and slide the metal case off the front. There is a rubber gasket around the front face that may or may not come along for the ride.

To access the fans, remove 4 more small Philips-head screws on the top of the exposed sheet metal chassis, near the rear. Gently lifting this up (note the wires connected to the components on the bottom of it), you can see the motherboard, fans, battery, and other internals. Mounted on the back of the now-loose part is the power supply. Carefully disconnecting the two Molex connectors will allow it to be completely detached. The power supply contains a number of fairly large, presumably still-charged, capacitors, so use some reasonable degree of caution and don’t stick a screwdriver in there.

The battery, which is zip-tied to the side of the chassis interior, appears to be a standard item, and supposedly keeps data in the write cache memory alive during a power outage. I noted the specs for future replacement, but didn’t bother ordering one at this point. It is marked:

P/N: 55-002011-01
3.7 V, Li-ion, 7500 mAh
Cell from Japan

This appears to be the same battery used in the Drobo b800i, which makes sense, since the b800i and b800fs are apparently the same hardware but with different software (the “fs” version is a traditional NAS, while the “i” version exposes itself via iSCSI).

The plastic cover on the rear can be removed by reaching into the case and gently retracting the 5 plastic tabs that hold it on: there is one in each corner, plus one in the center of the top rear.

Cooling fans

The two cooling fans are held in place by “plastic rivets”, which can be removed by pushing a thin metal tool, such as a nail or small screwdriver, through the hole in each corner of the fan, and pushing on the center of the rivet. They will pop right out the back. Alternately, you can work them out from the exterior of the case by working a thin prying tool under the rivet “head” and pulling it out. Be careful not to lose any of the rivet parts; each one consists of two pieces.

The noisy fan in my unit is labeled “ADDA DC Brushless Model AD0912UB-A70GL, DC 12 V, 0.30 A, 14P3” and has two wires, black and brown, connecting it to the mainboard. The connector is a small 3-pin connector, of which only two pins are used.

Based on a quick search, it appears the AD0912UB-A70GL (what a mouthful) is actually a pretty common item, with an exact replacement selling for under $15 at Newark and under $25 on Amazon. Per Octopart, it’s described as: 92x92x25mm, 12 VDC, 60 CFM, Ball Bearing, Ultra High Speed Fan. Newark gives us more specific specs: 56.6 CFM, 3300 RPM, 3.48 W, noise rating of 39.4 dBA. Filtering Newark’s catalog for 92mm square fans operating on 12V with 2 lead connectors gives some replacement candidates.

Although it’s possible to purchase the exact OEM part, the Bisonic BP922512H-W is about the same price, pushes more air (58.7 CFM), runs a bit slower (3000 RPM), and has a noise rating that’s slightly better (34 dBA). The power consumption is just a tad more at 3.94 W according to the datasheet. Looks good. I ordered two of them, figuring that if one fan had already failed, the remaining one might not be too far behind. Might as well do them both at once.

Swapping the parts

After waiting a few weeks for Newark to deliver the new fans, it was time to install them in place of the old ones. Because the new fans come with bare wire leads, some basic soldering is necessary to attach them to the small 3-pin connectors used to connect to the mainboard.

Rather than cutting and stripping the existing wires on the old fans, I noticed that the solder points attaching them to the fan PCB were easily accessible by peeling back the label in the center of the fan. A bit of heat applied to each solder blob got them loose. With that done, it was a simple matter to splice the wires together, and cover the joints with some small heat-shrink tubes. Black goes to black, and brown goes to red on the new fans.

Reassembly was straightforward. The new fans line up exactly with the existing chassis holes, and the existing plastic rivets seem to hold them firmly in place. After closing up the case and connecting power, both new fans spun up immediately at the beginning of the boot process. After a long weekend of “burn in” time (basically waiting to copy any data to the device in case one or both fans failed quickly), I’m ready to declare this repair project a success.