Teardown: inside a 3G microcell

August 17, 2015 // By Brian Dipert, EDN
Brian Dipert dissects another item of consumer electronics that has failed-in-service; although intended for the US market, there are many features of this device that will be common to global designs; some interesting ways of attempting to make the product "tamper-evident" - and a little bit of IC design history that is European-sourced.

I've admittedly had a bit of a love-hate relationship with AT&T's 3G MicroCell and its femtocell alternatives from Verizon Wireless and others. On the one hand, it continues to irritate me that instead of building out their own networks, they're requiring that customers buy (although some get 'em for free if they complain loud and long enough) a mini-cellular base station that routes cellular traffic over the customers' broadband connections, eating into customers' monthly broadband usage allocations in the process, and continuing to eat into customers' monthly cellular usage allocations even though the cellular network isn't being used. On the other hand, I can't complain about the resultant coverage-reliability boost, and I realise that it's not necessarily cost-effective for companies to expand coverage to low population density and/or challenging topology areas such the mountainous residence regions that I prefer.

A few weeks ago, I noticed that my AT&T-served iPhone 4S was no longer reporting that it was connected to "AT&T M-Cell" while at my Colorado home. A close look at my AT&T MicroCell there alerted me to the fact that only its front panel power LED was illuminated; the normally-lit LEDs indicating an active broadband connection, GPS "lock," and active local cellular network were extinguished. Several power cycles had no effect, nor did the unit respond to hard reset attempts. Another expired piece of tech... another teardown candidate.

Underneath the under-device information sticker, thumb-presses suggested what were confirmed by subsequent punctures to be two Philips head screws:


One of the analyses (PDF) I'd found during preparatory research indicated, "Upon unscrewing these, the orange bottom panel can be removed." Although this is true, reality was far more complicated than the statement (or at least my interpretation of it) implied. For several days, I strove to figure out how to pry off the bottom panel without doing substantial harm to the PCB behind it. Eventually, the simultaneous application of several screwdrivers did the trick; as you can see, AT&T and development partner Cisco didn't intend for the process to be either easy or permanent-damage-free:

Peer closely at the lower of the two photos above, and you might be able to tell which of the side panels was next to get prying attention...[continues]