I posted this a few weeks back to the AgTalk forum. I thought some might find my tale interesting.
Back in September 2009 I set up a 1.5 mile link between farmsteads using a pair of Ubiquiti NanoStation 5 Loco units (5 GHz WiFi--802.11a band). These proved very reliable through storms and power outages over the years until June 30, 2018 when the AP unit at this farmstead went dead almost with no reason, i.e. there had not been a recent nearby lightning strike, though a squall line had moved through a few hours before with some hail. Efforts to access the unit were unsuccessful that evening. The decision was made to climb the tower and replace the unit the next day which I did. The unit I replaced it with was in service on this farmstead for a short link and could be borrowed (the link was down anyway with the AP down). The replacement went smoothly and the replacement unit operated as the AP without issue. The old AP was reconfigured and put back in service for the link where the borrowed unit came from.
All was well until the afternoon of December 28, 2018 when the AP went down. I was able to access it on its factory default address and found that all settings had been reset to factory defaults. I uploaded the previously saved configuration and the unit ran normally for a couple of hours and then quit again. Efforts to access it were unsuccessful. The next morning, Dec 29, a Saturday, I was able to access it at the factory default address and rather than just upload the configuration again, I opted to update it to the latest firmware for the older NS5L which is AirOS 4.04. All went well for two days before it failed again and this time all efforts to access it over the network link failed.
After the failure in June I had ordered a pair of 5 GHz panel antennas with the intent of eventually replacing the NS5L at each end with Ubiquiti Bullet 5 units so the radio hardware could be accessed from ground level. I had failed to order the coaxial cable for this end, however. Rather than being able to climb the tower immediately I awaited the arrival of50 feet of LMR-400 cable terminated with N male connectors along with a PolyPhaser lightning arrestor, both ordered from Amazon on New Years Day. Both arrived on Saturday January 5, 2019 which was ideal since there was barely any wind and the high temperature hit 62F! The climb was completed with the NS5L removed and the panel antenna and coaxial cable installed with a single climb to the top.
At the bottom I connected the Bullet and it immediately went into firmware upload mode which caused a reset of the configuration to factory defaults. I went back and forth on this several times until some Web searching revealed that Ubiquiti incorporated a remote reset capability into their units but never documented it until the M units were released when, with AirOS 5, a setting was available to disable the remote reset. From what I found if voltage or ground (I don't recall which) is present on the data lines (pins 1,2,3 or 6 on the 8P8C connector), the unit will go into remote firmware upload mode. I swapped out the PoE injector with a known good one and the problem persisted which pointed to the cabling between the house and the Bullet.
The cable had been in place since the initial installation in 2009 and was run of the mill UTP (Unshielded Twisted Pair) Cat 5 cable with a black outer jacket. In the process of troubleshooting the Bullet I cut off the section that ran up the tower and terminated it with a new 8P8C connector that did not resolve the issue. As i have a box of Ubiquiti Tough Cable which is STP (Shielded Twisted Pair) Cat 5e the only choice was to replace the end between the PoE and the Bullet on Sunday which I did. Service was restored and has been solid since. I also replaced the aging Cat 5 UTP going to the WISP's Nanobeam that had supported three generations of their equipment and had a poor splice in it. A nice result of doing that for both links was that noise to my amateur radio station was greatly reduced and Ubiquiti equipment resets from my transmissions were also eliminated. A win win!
Thinking about it after things were working, even had I known about the remote firmware upload capability, it would not have mattered as the failure state was putting the unit into remote firmware upload continuously. I had tried the TFTP method to upload new firmware while the NS5L was in failure mode and could not successfully upload any firmware. Perhaps the older units did not fully implement the protocol. I later removed all the old cabling and didn't find any obvious damage. Perhaps the cabling just became contaminated over time. No water seeped out that I could tell.
To garner sparing I purchased 2 NOS Bullet M5 units and ordered what I thought were the correct PoE adapters for them. Turns out I missed the section on the PoE datasheet where it was shown that the ones I ordered put power on all four pairs while the units only accept power on 2 pairs-- pins 4,5,7 & 8. At least I was able to order the correct PoE adapters and return the incorrect ones for a refund (minus the shipping charge to send them back, a bit of stupid tax, I guess). Lesson learned, be careful to be sure the PoE and the powered device match though this information requires some careful reading to get right.
A bit more work remains as I plan to dig in a conduit to run the network cabling in between the tower and the entry point into the basement. That will wait until warmer weather!