Teardown: The DOCSIS 2.0 cable modem falls out of favor

-September 08, 2017

Back in April 2014, I picked up an open-box Motorola SB5101U cable modem for $14.49 with free shipping, as a backup to my existing cable modem. The SB5101U was a DOCSIS 2.0-based product, versus the then-latest DOCSIS 3.0 cable modems shipping from multiple suppliers (not to mention now-latest DOCSIS 3.1 successors). But the Internet broadband speed tier I was getting from Comcast wouldn't have taken advantage of beyond-DOCSIS 2.0 capabilities, anyway. And did I mention that the modem, one of the more popular options of the DOCSIS 2.0 era, was only $14.49?

2.5 years later, DOCSIS 3.0 cable modems are pretty darn inexpensive, too. And Comcast is growing increasingly un-fond of DOCSIS 2.0 devices. So instead of continuing to cling to the idea of potentially pressing the SB5101U into service someday, I decided to instead dissect it for your and my common curiosity-satisfaction pleasure ... hopefully in a non-destructive manner, so that I could then donate it for someone else to potentially press into service.

I'll begin with a series of box shots:











I was particularly fond of the following messaging on the external-package markings; if you're a long-time reader, you're not surprised:


Flip back the box top and here's the first thing you'll see:


Underneath the cable modem itself, which we'll see more of shortly, Motorola also included Ethernet and USB cables, a documentation-and-software CD, various pieces of paperwork, and a power supply:


Here's a closeup of the "wall wart," revealing relevant output voltage/current and plug polarity specs, among other things:


Now for some outside shots of the modem itself. According to this discussion thread, the SB5101U is the "retail" version of the service provider-bundled SB5101, and also adds both a standby button and a USB interface option (in addition to obligatory Ethernet):








Believe it or not, the torx on the back of the unit, above the Ethernet port, is the sole screw holding the chassis together:


I thought there might be more at the underside, under the sticker, but I found only plastic tabs there:



After removing the screw (thank you once again, iFixit toolkit) and popping the tabs, I was able to pry the two halves apart from the back:


I never got the front side separated, but was still able to slip out the PCB in the middle:


Note the light guides intended to route the PCB-located LEDs' outputs to the front panel:


Voila: the PCB topside:


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